STEMscopes Science Florida - Comprehensive 3

OKLAHOMA 3D K-12 SCIENCE Florida STEMscopes Science Comprehensive Science 3 STEMscopedia ISBN: 979-8-88826-220-7 Published by Accelerate Learning Inc., 5177 Richmond Ave, Suite 800, Houston, TX 77056. Copyright © 2024, by Accelerate Learning Inc. All rights reserved. No part of this publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without prior written consent of Accelerate Learning Inc., including, but not limited to, in any network or other electronic storage or transmission, or broadcast for distance learning.

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10 9 8 7 6 5 4 3 2 1

OKLAHOMA 3D K-12 SCIENCE

Comprehensive Science 3 STEMscopedia Table of Contents Lesson

Introduction to o Space

Life Cycles of Stars

Celestial Objec cts

Gravity Characteristics s and Us se of th he Electromagnetic c Specttrum

Earth’s Tilt and d Season ns

Ocean Tides

Solids, Liquids,, and Ga ases

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1 17 37 55 65 81 95 109 iii

OKLAHOMA 3D K-12 SCIENCE

Comprehensive Science 3 STEMscopedia Table of Contents

Lesson

Page

127

Physical and Chemical Chang ges

141

Elements and Compoun nds

153

Elements and the Perio odic Ta able

165

Metals, Nonme etals, and d Meta alloids

179

Aqueous Solutio ons

193

Relative Densitty

207

Pure Substance es and Mixture es

223

Properties of Acids and d Bases s

Photosynthesis s and Ce ellular Respirration

iv

237

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OKLAHOMA 3D K-12 SCIENCE

Comprehensive Science 3 STEMscopedia Table of Contents

Lesson

Page

249

The Carbon Cyc cle

Appendix Glossary

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261

v

Introduction to Space

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1

STEMscopedia Think about It When you look up at the night sky, thousands of objects sparkle into view. If you gazed through a telescope, you would see many more of these objects. You would be observing stars, which give off energy in the form of visible light. However, the stars you can see are only a very small portion of the universe. What objects in space, other than stars, make up the universe? What kinds of energy, other than light, do these objects give off? And how do scientists answer these and other questions about objects that are so far away?

in objects an t a h 1. W ht sky c igg the n hink of? you t

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Introduction to Space | 3

STEMscopedia The universe contains everything that exists—from particles of matter smaller than an atom to the largest stars. Within the universe, there are billions of galaxies, and each galaxy contains billions of stars. The universe also includes all forms of energy, from the light you see streaming from stars to invisible radio waves and X-rays.

Scientists use the astronomical unit (AU) to measure distances within our solar system. One AU is the mean distance between Earth and the Sun: 150 million km. Beyond our solar system, however, distances are so large that even AUs are not convenient units for measuring distance. Instead, scientists use a unit called the light-year (LY). Because this unit contains the word year, it may seem to be measuring a quantity of time. However, a light-year is actually a unit of distance. One light-year equals the distance light travels in one year. Light travels at about 300,000 kilometers/second (km/s); this is the speed of light. Light travels 9,460,800,000,000 km per year. That means 1 LY equals nearly 9.5 trillion km, or approximately 63,000 AU. Even relatively close stars may be separated by dozens of light-years. Imagine trying to measure these distances in kilometers or astronomical units!

Even time is part of the universe. Scientists think of time as beginning when the universe began.

The most distant objects that have been detected are about 13.7 billion light-years away from Earth.

Again, a light-year is a unit of distance, equal to the distance traveled by light in one year, which is approximately 9.5 trillion km. This means that light from the most distant objects that scientists have observed began the journey to Earth 13.7 billion years ago! If these objects are actually the most distant objects in space, they are also the farthest back in time. For these reasons, scientists estimate the universe is about 13.7 billion years old.

4 | Introduction to Space

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STEMscopedia To learn about the properties of objects in space, scientists study the energy coming from these objects.

The energy may be in the form of visible light or other components of the electromagnetic spectrum, such as radio waves and X-rays. The electromagnetic spectrum is an arrangement of forms of energy that travel through space in waves. Objects in space emit these forms of energy in different patterns.

Scientists use special telescopes to detect these patterns and learn about the objects emitting them.

ntists ie c s do 2. How e distances r measu space? in

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Introduction to Space | 5

STEMscopedia From its birth to the present, the universe has changed tremendously. Gravity has pulled huge pockets of gas together to form stars. In turn, these stars have been drawn together by gravity to form families of billions of stars. Stars born long ago developed, aged, and died. This process goes on today, and it will continue to go on in the future. <RX PD\ KDYH GLI¿ FXOW\ LPDJLQLQJ KRZ JUDYLW\ FDQ ³SXOO WRJHWKHU´ JDVHV WR IRUP VWDUV 5HPHPEHU WKDW gases, like all forms of matter, are composed of particles in motion. These particles are tiny, but they have mass; so, they are affected by gravity. As the density of a gas increases, gas particles collide more frequently and with greater force, causing the gas’s temperature to increase as well. Eventually, gases can become so hot that they ignite, forming huge, burning spheres, or stars.

Almost everything you see in the night sky with your unaided eyes is a star. Exceptions include a few planets of our solar system, Earth’s Moon, and an occasional comet. A star is a huge ball of gas that produces its own energy, mostly through nuclear reactions in its core. Gravity holds together the particles that make up the body of a star. In other words, a star is so massive, it is held together by its own gravity.

Galaxies are made of millions of stars, interstellar gas, and dust that stay relatively close together due to gravitational attraction. Every star you see in the night sky is part of a galaxy called the Milky Way. This is our home galaxy. The Milky Way is only one of billions of galaxies in the universe, each of which contains hundreds of billions of stars, gases, and dust held together by the force of gravity.

Most galaxies are invisible to the unaided eye, but if you have keen vision, you might spot one on a clear night. It would look like a faint, fuzzy patch of light. Viewed through powerful telescopes, JDOD[LHV DSSHDU LQ YDULRXV VKDSHV 7KH VKDSH RI D JDOD[\ FDQ EH FODVVL¿ HG DV HOOLSWLFDO VSLUDO OHQWLFXODU (lens-shaped), or irregular.

6 | Introduction to Space

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STEMscopedia Galaxy Shapes Elliptical: Spherical or flattened disk Spiral: A nucleus of bright stars and two or more spiral arms Irregular: No definite shape Lenticular: Much like elliptical To better understand the hierarchical relationships between planets and other celestial objects relative to solar systems, galaxies, and the universe, look at the image below. It shows Earth and all the planets that revolve around the Sun. A planet or group of several planets that revolve around a star is known as a solar system. This shows that our solar system belongs to the Milky Way galaxy. The Milky Way galaxy and approximately 30 other galaxies are lumped together in what is called the local group.

This local group is one of 100 galaxy groups and clusters that are part of the local supercluster. Billions of solar systems make up a galaxy. Billions of galaxies make up the universe.

THE UNIVERSE

THE LOCAL SUPERCLUSTER THE LOCAL GROUP

THE MILKY WAY GALAXY

EARTH

THE SOLAR SYSTEM

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Introduction to Space | 7

STEMscopedia y are h W .

3 made s e ie x la ga iillions b f o up s? of star

+XPDQV KDYH ZRQGHUHG DERXW VSDFH IRU WKRXVDQGV RI \HDUV EXW ZKHQ GLG WKH VFLHQWL¿ F H[SORUDWLRQ RI space begin? One possible answer is 1610, when an Italian scientist and inventor named Galileo Galilei looked at the night sky through a telescope. Before Galileo, telescopes were useful for seeing distances only on Earth. They were not powerful enough to give scientists clear views of space.

Telescopes on Earth are limited by interference from the planet’s atmosphere and from human-made lights, which make distant stars appear less bright. One way to avoid this light pollution is to launch telescopes into space. For example, in 1990 scientists launched the Hubble Space Telescope, which orbits Earth at a distance of about 550 km. The Hubble gives a clear view of space without interference from Earth’s atmosphere or light pollution.

Humans have been able to move beyond the limitations of studying space through simple telescopes, however. Due to continued technological improvements to telescopes and other instruments, scientists have made great advances in knowledge about the solar system and the stars beyond. This knowledge has made it possible for humans to design space suits, tools, and vehicles so that astronauts can safely travel beyond Earth’s surface.

8 | Introduction to Space

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STEMscopedia space plummet far below 0°C, the freezing point of water. At the bottom of some craters on the Moon, WHPSHUDWXUHV KDYH EHHQ PHDVXUHG DW OHVV WKDQ í & í ) 2[\JHQ ZKLFK VXVWDLQV OLIH RQ Earth, is absent on the Moon and in space (known as the vacuum of space) because of the microgravity environment. Without gravity to support them, human bones and muscles can become extremely weak.

Additionally, harmful radiation from the Sun and other parts of the galaxy shoots through space. This radiation has so much energy that it can destroy living tissue that is not protected by special suits.

To overcome these conditions, engineers have designed life-support systems for astronauts. These include space suits, space capsules, space vehicles, and space habitats that protect humans against the harmful effects of the space environment. The table lists some of the technologies that have been created to help humans in space.

Space Technology

Description

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This life preserver, worn like a backpack, contains compressed nitrogen gas. $Q DVWURQDXW À RDWLQJ DZD\ IURP D VSDFH YHKLFOH UHOHDVHV MHWV RI QLWURJHQ WKDW WKUXVW WKH DVWURQDXW LQ WKH GLUHFWLRQ RSSRVLWH WR ZKHUH WKH JDV LV À RZLQJ (9$ VWDQGV IRU ³H[WUDYHKLFXODU DFWLYLW\ ´ RU DFWLYLW\ RXWVLGH D VSDFH YHKLFOH

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These are unmanned robot vehicles used to explore the surface of Mars.

Curiosity ZDV WKH ¿ y UVW 1$6$ URYHU WKDW ODQGHG RQ 0DUV RQ $XJXVW The vehicle was programmed to take measurements, collect data, store information, and then communicate the information back to Earth.

Helmet

An astronaut’s helmet includes a clear visor with an extremely thin layer of JROG WR ¿ OWHU RXW KDUPIXO UDGLDWLRQ 7KH KHOPHW DOVR SURWHFWV WKH DVWURQDXW IURP debris and other small objects whizzing through space. It contains earphones and a microphone for communicating with other astronauts.

Extravehicular DFWLYLW\ (9$ gloves

7R ZRUN LQ VSDFH DVWURQDXWV PXVW EH DEOH WR HDVLO\ PRYH WKHLU ¿ QJHUV ZLWKRXW exposing them to radiation and freezing temperatures. To do this, they wear (9$ JORYHV 7KH ¿ QJHUV RI WKHVH JORYHV DUH YHU\ À H[LEOH DQG HTXLSSHG ZLWK heaters. The gloves are connected to each space suit’s arms in a way that allows astronauts to turn their wrists.

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To keep warm on a cold day, you might pull on long underwear. Unfortunately, if you work up a sweat outside, you might soak your underwear. Astronauts wear something similar to long underwear; however, the LCVG helps to keep them cool and dry as they work in space. It is webbed with over 90 m of narrow tubing. Water is pumped from a special backpack through the tubes to cool the astronaut’s body. Vents in the underwear move any sweat the astronaut produces while working away from the astronaut’s skin.

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The inner three layers of an astronaut’s space suit make up the LCVG. However, a space suit contains 11 more layers! The vacuum of space applies almost no pressure to an astronaut’s body. A bladder layer directly above the LCVG is designed to apply the pressure the human body needs to function properly. Among the remaining layers are seven made of a special plastic that acts like insulation. These layers keep temperatures stable near the astronaut’s body. The outer layer of a space suit is made of three materials that form a ¿ UH UHVLVWDQW ZDWHUSURRI EDUULHU DJDLQVW VSDFH REMHFWV

Communication

Astronauts must use complex radios and computers to communicate with one another and with a mission team on Earth. These instruments also help them conduct research and repair damaged equipment and satellites.

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Introduction to Space | 9

STEMscopedia particles. This is how astronauts there can talk to each other—and breathe!—as they would on Earth.

However, astronauts working outside the space station require special radios, video devices, and computers to communicate with each other and with scientists on Earth. These devices transform the sounds the astronauts make into forms of energy that can be transmitted through space. The construction of the International Space Station began in 1998. Positioned as a satellite in low Earth RUELW LW LV D IDFLOLW\ IRU VFLHQWLVWV WR SHUIRUP VSDFH UHVHDUFK DQG VSDFHFUDIW WHVWLQJ ,Q WKH ¿ UVW FRPPHUFLDO À LJKWV WR WKH ,QWHUQDWLRQDO 6SDFH 6WDWLRQ EHJDQ DIWHU WKH UHWLUHPHQW RI 1$6$¶V VSDFH VKXWWOH À HHW

10 | Introduction to Space

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STEMscopedia ,Q WKH 8QLWHG 6WDWHV WKH 1DWLRQDO $HURQDXWLFV DQG 6SDFH $GPLQLVWUDWLRQ 1$6$ RYHUVHHV VSDFH H[SORUDWLRQ 1$6$ ZDV IRUPHG LQ ZLWK WKH ¿ UVW VSDFH RSHUDWLRQV ORFDWHG DW WKH &DSH &DQDYHUDO $LU )RUFH 6WDWLRQ HDVW RI 2UODQGR )ORULGD $ IHZ \HDUV ODWHU LQ DOO 1$6$ RSHUDWLRQV ZHUH PRYHG WR WKH .HQQHG\ 6SDFH &HQWHU .6& RQ 0HUULWW ,VODQG )ORULGD 1$6$ FKRVH )ORULGD DV D ODXQFK FHQWHU because it is close to the equator. A rocket launched near the equator needs less fuel to reach orbit.

6LQFH 1$6$ KDV EHHQ UHVSRQVLEOH IRU ODXQFKLQJ SUREHV VDWHOOLWHV URYHUV YDULRXV VSDFHFUDIWV Skylab, and the International Space Station.

Scientists pursue space exploration to answer questions not only about our place in the universe but DOVR DERXW WKH KLVWRU\ RI WKH XQLYHUVH LQFOXGLQJ WKH KLVWRU\ DQG IRUPDWLRQ RI RXU VRODU V\VWHP 1$6$ reports that space exploration has had a great impact on society, contributing to advances in technology, improvements in the economy, and connections with nations around the world.

Space exploration impacts Florida’s economy in many ways. Through rocket launches, launch sites, DQG RWKHU DFWLYLWLHV 1$6$ FRQWULEXWHV DERXW IRXU ELOOLRQ GROODUV WR WKH VWDWH¶V HFRQRP\ HDFK \HDU )RU LQVWDQFH 1$6$ UHQWV WKHLU ODXQFK IDFLOLWLHV WR SULYDWH EXVLQHVVHV DQG WKH PLOLWDU\ 7KLV DWWUDFWV DGGLWLRQDO industries to establish their operations within the state.

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Introduction to Space | 11

STEMscopedia innovations in different areas, including health, medicine, consumer goods, transportation, renewable HQHUJ\ DQG PDQXIDFWXULQJ :KHQ EXVLQHVVHV WUDQVIRUP 1$6$ WHFKQRORJLHV WR GHYHORS QHZ FRPPHUFLDO SURGXFWV DQG VHUYLFHV LW QRW RQO\ EHQH¿ WV WKH UHJLRQDO HFRQRP\ EXW DOVR VLJQL¿ FDQWO\ VWUHQJWKHQV WKH nation’s competitiveness in the global marketplace. ,Q DGGLWLRQ ZRUN DQG UHVHDUFK E\ 1$6$ VFLHQWLVWV KDYH OHG WR WKH GHYHORSPHQW RI PDQ\ SURGXFWV 6RPH H[DPSOHV DUH LQIUDUHG HDU WKHUPRPHWHUV WKHUPDO EODQNHWV ¿ UH UHVLVWDQW PDWHULDOV /(' OLJKWV ZDWHU SXUL¿ FDWLRQ V\VWHPV DHURJHO LQVXODWLRQ EUHDWKLQJ DSSDUDWXVHV XVHG E\ ¿ UH¿ JKWHUV DQG HYHQ WKH FRUGOHVV YDFXXP 5HVHDUFK IURP ORQJ PLVVLRQV KDV EHHQ DSSOLHG WR LPSURYHG SURFHVVHV IRU IRRG preservation and nutritional enrichment.

Space exploration has also affected the culture of Florida. The creation of the space program in 1958 provided federal funding for education, especially in mathematics, science, engineering, and modern foreign languages. To educate and prepare Florida’s students to work in the space industry, new science and math programs were created, and existing programs were strengthened. Space became an integral SDUW RI )ORULGD¶V FXOWXUH DV 1$6$¶V PLVVLRQV SOD\HG D ELJ UROH LQ LWV KLVWRU\ WHFKQRORJ\ DQG HGXFDWLRQ 1$6$ FRQWLQXDOO\ VHHNV WR HGXFDWH WKH SXEOLF E\ VKDULQJ LQIRUPDWLRQ GDWD DQG LPDJHV WKH\ KDYH collected on their website, allowing students to talk to astronauts, and providing them opportunities to YLHZ ODXQFKHV ¿ UVWKDQG Many high-tech industries have developed in Florida, and workers are drawn to the state for new opportunities in aerospace careers. After the successful Apollo launches and subsequent change in GLUHFWLRQ RI 1$6$¶V PLVVLRQ DQG JRDOV PDMRU SRUWLRQV RI WKH .HQQHG\ 6SDFH &HQWHU¶V 1$6$ SHUVRQQHO and members of the area’s space-related workforce left for high-tech and military career opportunities.

Yet thousands of native Floridians and recruited workers stayed on, serving the nation’s drive to explore space. Since then, an entire generation of space-industry workers has retired to the Space Coast area. Other initiatives have arisen, including environmental services and solar-energy technology development.

After six decades of space-age development, Florida remains one of the nation’s top centers for technology and manufacturing industries. It still serves as the home of one of the world’s most VLJQL¿ FDQW VSDFHSRUWV

what n I .

4 space s a h s way ation explor ORULGD" WHG ) EHQHŞ

12 | Introduction to Space

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STEMscopedia 6WHSKHQ +DZNLQJ ± 3K\VLFLVW DQG &RVPRORJLVW %ODFN KROHV ZHUH D IRFXV IRU RQH RI WKH JUHDWHVW VFLHQWL¿ F WKLQNHUV RI WKH SDVW FHQWXU\ 6WHSKHQ +DZNLQJ (YHQ WKRXJK +DZNLQJ KDG D GLVHDVH WKDW FRQ¿ QHG KLP WR D ZKHHOFKDLU DQG SUHYHQWHG KLP from speaking, he developed a number of theories about black holes. Hawking communicated his ideas through an electronic device that converted the movements of muscles in his cheeks into words.

Hawking argued that black holes were created at the birth of the universe and have been with us ever since. In the beginning, they may have been no larger than single protons. Today, however, some are thought to be so large that they form the cores of galaxies.

Although the concept of black holes is still being investigated, scientists have several theories about how they form and affect nearby matter and energy. As extremely massive stars age, they begin to collapse.

Scientists think the matter in these stars is drawn inward, creating an extremely small yet dense object.

A black hole the size of a pea could have the mass of Earth! Scientists once assumed the gravity of black holes pulled everything into them forever, like super-powerful whirlpools. However, Hawking theorized that black holes give off some kinds of radiation. If so, black holes should be detectable. As it turns out, scientists have uncovered evidence of a black hole at the center of our very own galaxy!

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Introduction to Space | 13

STEMscopedia The universe contains billions of galaxies, which contain billions of stars, solar systems, and planets all held together by gravity. The distances between these astronomical bodies are so vast that they must be measured in light-years. A light-year is the distance that light travels in one year, which is approximately 9.5 trillion km. Advancements in space technology, such as space suits, rovers, and communication WRROV KDYH KHOSHG VDWLVI\ RXU FXULRVLW\ RI VSDFH H[SORUDWLRQ 1$6$¶V FRQWULEXWLRQV LQ )ORULGD KDYH KDG D positive effect on Florida’s economy and culture.

Connect It :KDW REMHFWV LQ VSDFH EHVLGHV VWDUV PDNH XS WKH XQLYHUVH" The universe is made up of all of space and the matter it contains. Planets orbit the stars in solar systems. Billions of stars are found in galaxies. Billions of galaxies are found in the universe. All of this is bound together by gravity.

14 | Introduction to Space

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STEMscopedia 1

Galaxies contain billions of what? $ Black holes B Stars C Universes D Smaller galaxies

2

Which statement most accurately describes what we know about space? $ The galaxy contains thousands of universes, and each universe contains millions of stars.

B The universe contains hundreds of galaxies, and each galaxy contains thousands of stars.

C The galaxy contains hundreds of universes, and each universe contains thousands of stars.

D The universe contains billions of galaxies, and each galaxy contains billions of stars.

3

Distances in space are measured in– $ light-years.

B kilometers.

C miles.

D seconds.

4

Due to continued technological improvements, scientists have gained much knowledge about the solar system and the stars beyond. What was the earliest technology that allowed humans to gather information about remote objects in space? $ Space shuttle B Telescope C Thermometer D Microscope

5

:KDW KDYH VSDFH UHVHDUFK DQG H[SORUDWLRQ 127 FRQWULEXWHG WR LQ )ORULGD" $ Increase in employment B Increase in tourism C Increase in plants and animals D ,QFUHDVH LQ VFLHQWL¿ F NQRZOHGJH

6

Fill in the blanks with the missing words.

Planets – Solar system – _____________ – _____________ – Universe

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Introduction to Space | 15

Life Cycles of Stars

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17

STEMscopedia You may have heard it said that we are made from the stuff of stars. Stars go through a life cycle just like we do. They are born, they live and undergo change, and they die. How have scientists learned so much about stars if we are somewhat new to space travel? And how do we know what stars are made of?

ppens a h t a 1.. Wh star dies? a when

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Life Cycles of Stars | 19

STEMscopedia *UDYLW\ LV GH¿ QHG DV WKH DWWUDFWLYH IRUFH EHWZHHQ DOO WKLQJV ZLWK PDVV 7KH 6XQ¶V SRZHUIXO JUDYLW\ NHHSV the rest of the solar system in orbit around the Sun. The planets and moons keep their orbits based on the gravity of the planets and the Sun. The asteroids in the asteroid belt stay in orbit based on gravity of the Sun. Comets also stay in orbit around the Sun due to the gravity of the Sun but can be pulled off FRXUVH E\ D SODQHW¶V JUDYLW\ LI WKH\ JHW WRR FORVH WR D SODQHW

What Is a Star?

Stars have fascinated humans for generations. A star is a celestial body consisting of a mass of gas held together by its own gravity. The energy that powers the star is generated by nuclear reactions in its interior. Stars consist of mainly hydrogen (H), which is converted to helium (He) throughout its lifetime through nuclear fusion. Scientists use this fact to help determine the ages of stars—the ratio of hydrogen to helium helps determine where the star is in its life cycle. Older stars have more helium, while younger stars contain more hydrogen.

In nuclear fusion, two lighter atoms join to form a heavier one, and a tremendous amount of visible and infrared electromagnetic radiation, thermal and light energy, is released. The resulting compound is actually lighter than the two original atoms.

Nuclear Fusion in Stars Hydrogen isotopes

Helium

Neutron Hydrogen isotopes Electromagnetic radiation, thermal and light energy

20 | Life Cycles of Stars

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STEMscopedia The force that keeps stars from simply exploding is gravity. The balance between nuclear fusion and JUDYLW\ FRQWLQXHV WKURXJKRXW D VWDU¶V OLIHWLPH XQWLO LW UXQV RXW RI K\GURJHQ DOORZLQJ JUDYLW\ WR WDNH RYHU and cause the star to collapse.

2. De proces scribe the s fusion of nuclear stars that moves t differe hrough the nt sta ge their life cy s in cles.

the only star in our solar system. There are two basic kinds of stars, and each follows its own pathway WKURXJKRXW LWV OLIHWLPH +RZ D VWDU LV FODVVL¿ HG GHSHQGV RQ LWV PDVV Stars are incredibly important to life and to human existence. Many of the elements and compounds necessary for life have been formed for billions of years inside the cores of stars. Without stars, the raw materials for life would not be in the universe, so we likely would not exist.

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Life Cycles of Stars | 21

STEMscopedia There are two main kinds of stars—those with low mass and those with high mass relative to the Sun. 6WDUV UDQJH LQ VL]H IURP ± NP ZLGH WR PRUH WKDQ WLPHV WKH 6XQ¶V GLDPHWHU 7KRVH WKDW DUH VPDOOHU WKDQ WZR WLPHV RXU 6XQ¶V PDVV DUH FDOOHG ORZ PDVV VWDUV DQG WKRVH JUHDWHU WKDQ WZLFH WKH PDVV RI RXU 6XQ DUH FDOOHG KLJK PDVV VWDUV /RZ PDVV VWDUV DUH PXFK PRUH FRPPRQ WKDQ KLJK PDVV VWDUV 7KH OLIH VSDQ RI D VWDU UDQJHV IURP WHQV RI PLOOLRQV WR WULOOLRQV RI \HDUV IRU ORZ PDVV VWDUV ,W LV PXFK VKRUWHU IRU KLJK PDVV VWDUV EHFDXVH WKH\ fuse their hydrogen into helium at a much faster rate.

Low-Mass Stars /RZ PDVV DQG KLJK PDVV VWDU F\FOHV KDYH VRPH VLPLODULWLHV 2QH RI WKHP LV IRXQG DW WKH EHJLQQLQJ RI D VWDU¶V OLIHWLPH $OO VWDUV EHJLQ OLIH LQ D nebula—a large cloud of dust and gas in space. The root of the word nebula comes from the Latin word for mist, vapor, or fog. Nearly all nebulae are lit by starlight, and they are relatively cool with temperatures ranging between 10 and 30 kelvins. These areas in space are known as stellar nurseries. Gravity in these massive clouds pulls together material in clumps, which collapse in on themselves and form hot inner cores. These are called protostars. At this time, the baby VWDU LV QRW KRW HQRXJK WR FRQGXFW IXVLRQ DV LW LV RQO\ DERXW NHOYLQV (YHQWXDOO\ WKRXJK WKH VWDU¶V temperature increases enough to start nuclear fusion, which is the process that provides fuel for stars.

At the same time, the energy given off by fusion must act against the force of gravity inside the star.

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7KLV LV WKH KRUVHKHDG QHEXOD ORFDWHG DERXW OLJKW \HDUV IURP (DUWK LQ WKH FRQVWHOODWLRQ 2ULRQ 22 | Life Cycles of Stars

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STEMscopedia main sequence is a FDWHJRU\ RI VWDEOH VWDUV WKDW DUH LQ WKH PLGGOH GHYHORSPHQWDO SKDVHV 'XULQJ WKLV VWDJH DERXW RQH WKLUG RI WKH VWDU¶V K\GURJHQ DWRPV ZLOO IXVH DQG EHFRPH KHOLXP DWRPV 'XULQJ WKLV VWDJH QXFOHDU IXVLRQ EHJLQV ZKHQ WKH LQWHULRU RI WKH VWDU UHDFKHV NHOYLQV 5RXJKO\ RI D VWDU¶V OLIH F\FOH LV VSHQW LQ WKH PDLQ VHTXHQFH VWDJH 2XU 6XQ LV FODVVL¿ HG DV D PDLQ VHTXHQFH VWDU DQG PD\ KDYH VSHQW 50 million years reaching this stage.

'XULQJ WKH PDLQ VHTXHQFH VWDJH WKH UDWH RI IXVLRQ PDWFKHV WKH UDWH DW ZKLFK WKH VWDU JLYHV RII HQHUJ\ and the force of gravity continues to hold the star together, so the star is stable. $V WKH PDLQ VHTXHQFH VWDU XVHV XS PRVW RI LWV UHPDLQLQJ K\GURJHQ LW FDQQRW FRQWLQXH PDNLQJ LWV RZQ heat. The core of the star contracts while the gas layers expand, which makes the star grow massive LQ VL]H ,W PD\ UHDFK D GLDPHWHU WLPHV LWV PDLQ VHTXHQFH VL]H $V LW H[SDQGV LW WXUQV UHG DQG WKH remaining helium fuses to form carbon. Then, as fusion continues, oxygen, silicon, nitrogen, and iron are formed. These are the basic elements involved in the creation of life.

Stars at this stage are called giants. Giant stars have larger diameters and lower surface temperatures than average stars and are formed when the fuel center of an average star is depleted. This is because the core of the star is collapsing in on itself since the force of gravity is stronger than the force of nuclear fusion. The star gives off more energy as it expands, making it brighter. As more mass is added to the shrinking core of the star, gravity becomes stronger, making the star continue to collapse as its outer layers continue to expand.

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Life Cycles of Stars | 23

STEMscopedia part of nebulae that will eventually coalesce or gather into new protostars. This is called a planetary nebula. A planetary nebula LV D FORXG RI LQWHUVWHOODU GXVW DQG JDV FUHDWHG E\ D G\LQJ DYHUDJH VL]HG star. Scientists estimate that there are about 10,000 planetary nebulae in our galaxy alone. They are relatively common, but a short phase in the stellar life cycle, only lasting about 25,000 years. They are so named because they look somewhat like planets.

7KLV LV 0HVVLHU D SODQHWDU\ QHEXOD LQ RXU RZQ JDOD[\ ,W LV DERXW OLJKW \HDUV IURP (DUWK LQ WKH FRQVWHOODWLRQ 9XOSHFXOD ,W ZDV WKH ¿ UVW SODQHWDU\ QHEXOD GLVFRYHUHG As much of the outer part of a star is blown away and forming a planetary nebula, the dense carbon core of the star collapses and becomes a white dwarf. A white dwarf LV WKH ¿ f QDO VWDJH RI WKH OLIH F\FOH RI an average star. It is formed after the star expels its outer material into a planetary nebula, leaving the ZKLWH KRW FRUH EHKLQG :KLWH GZDUI VWDUV GR QRW KDYH HQRXJK PDVV WR H[SORGH DV D VXSHUQRYD 7KH ¿ QDO VWDJH LQ D ORZ PDVV RU DYHUDJH VWDU¶V OLIH F\FOH LV WKDW RI D EODFN GZDUI 7KH XQLYHUVH DV D ZKROH LV WRR \RXQJ IRU DQ\ RI WKHVH WR KDYH IRUPHG VFLHQWLVWV HVWLPDWH LW ZRXOG WDNH TXDGULOOLRQV RI \HDUV WR form. It is also thought that these would not emit radiation or light but would have some kind of effect on objects around them.

24 | Life Cycles of Stars

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STEMscopedia Life Cycle of a Low-Mass Star

Stellar nebula

Average star

Red giant

Red supergiant

Planetary nebula

White dwarf

e the e b i r c s 3. De lements lik and f e role o n, helium, s e r’ hydrog n in a sta carbo cle. life cy

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Life Cycles of Stars | 25

STEMscopedia +LJK PDVV VWDUV DUH WKRVH ZLWK PXFK PRUH PDVV WKDQ WKH 6XQ 7KH ¿ UVW WZR VWDJHV RI D KLJK PDVV VWDU¶V OLIHWLPH DUH WKH VDPH DV WKRVH RI ORZ PDVV VWDUV %RWK IRUP IURP D QHEXOD DQG VSHQG PRVW RI WKHLU WLPH LQ WKH PDLQ VHTXHQFH VWDJH $ KLJK PDVV VWDU KDV PXFK PRUH K\GURJHQ WR ZRUN ZLWK KRZHYHU VR LW SURJUHVVHV WKURXJK WKH PDLQ VHTXHQFH VWDJH PXFK PRUH TXLFNO\ WKDQ D ORZ PDVV VWDU +LJK PDVV VWDUV H[SDQG DW WKH HQG RI WKHLU PDLQ VHTXHQFH VWDJH MXVW OLNH ORZ PDVV VWDUV %HFDXVH WKH FRUH WHPSHUDWXUHV RI WKHVH VWDUV DUH PXFK KLJKHU WKDQ LQ ORZ PDVV VWDUV WKH\ JHQHUDWH D KXJH DPRXQW RI energy. The force of gravity increases, which causes the core temperature to rise even more. As the temperature tops 600 million kelvins, carbon begins to fuse into other heavier elements like oxygen, nitrogen, and eventually, sulfur and iron. A supergiant is a star with a larger diameter and lower surface temperature than a massive star; it is formed when the fuel center of a massive star is depleted. %HWHOJHXVH WKH EULJKW VWDU WKDW IRUPV 2ULRQ¶V OHIW VKRXOGHU LV D VXSHUJLDQW :KHQ WKH VWDU¶V FRUH FRQWDLQV RQO\ LURQ QR PRUH HQHUJ\ LV SURGXFHG 7KH VWDU EHJLQV WR FROODSVH XQGHU its own weight because of the massive gravitational force. Core temperatures rise to about 100 billion degrees, causing a huge shock wave and an explosion called a supernova. This sudden expelling of HQHUJ\ IRUPV KHDYLHU HOHPHQWV 7KH H[SORVLRQ LV VR SRZHUIXO LQ IDFW WKDW LW SURGXFHV ; UD\V DQG JDPPD UD\V LQ MXVW D IHZ VHFRQGV WKDW HTXDO WKH WRWDO DPRXQW RI HQHUJ\ PDLQ VHTXHQFH VWDUV HPLW LQ WKHLU lifetimes. This extraordinary amount of energy pushes the heavier elements like carbon and nitrogen away from the core of the star. Some of this material forms nebulae that eventually become new stars, SODQHWV RU HYHQ OLIH IRUPV The remnants of these explosions sometimes become neutron stars. A neutron star LV WKH ¿ QDO VWDJH of the life cycle for massive stars and is formed after the star completely runs out of fuel and collapses HYHU\ UHPDLQLQJ SURWRQ LQ WKH FRUH LQWR D QHXWURQ 7KH /*0 SXOVDU LV DQ H[DPSOH RI D QHXWURQ VWDU WKDW VSLQV TXLFNO\ 1HXWURQ VWDUV DUH VPDOOHU RQHV WKDW DUH DPD]LQJO\ GHQVH 7KH\ FRQWDLQ PRUH PDVV than the Sun but are only a few miles across.

If a supernova still has too much mass to become a neutron star after exploding, it may become a black KROH 7KH SUHVHQFH RI EODFN KROHV ZDV GHVFULEHG LQ (LQVWHLQ¶V WKHRU\ RI UHODWLYLW\ ,W VWDWHG WKDW D GHQVH VWDU FRUH¶V JUDYLW\ FRXOG RYHUFRPH RWKHU IRUFHV LI WKH FRUH ZDV ELJ HQRXJK $ black hole is the remains of a star or other large object that collapsed under its own gravity to form a superdense object with gravity so strong that light cannot escape its pull. These bodies easily attract matter and energy near WKHP DQG FDQ RQO\ EH VSRWWHG EHFDXVH VFLHQWLVWV FDQ REVHUYH WKH HIIHFW RI WKH EODFN KROH¶V JUDYLW\ RQ stars and gases near the black hole. They cannot be seen on their own.

26 | Life Cycles of Stars

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STEMscopedia Life Cycle of a High-Mass Star Black hole

Main sequence

Red giant/ supergiant

Supernova Neutron star

The following table compares the characteristics of both kinds of stars.

Low-Mass Stars

High-Mass Stars

Mass Relative to the Sun

Smaller than two times the 6XQ¶V PDVV

Larger than two times the 6XQ¶V PDVV

Overall Life Span

10 billion years

8 billion years

Stage of a Dying Star

Planetary nebula

Supernova

Final Stage

White dwarf

Neutron star or black hole

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Life Cycles of Stars | 27

STEMscopedia mass w o l pare ss 4. Com to high-ma f stars in terms o stars and overall mass span. life

The progression of a star through its life cycle can be plotted on a scatterplot invented by Danish astronomer Ejnar Hertzsprung and American Henry Norris Russell. It shows relationships between the temperature or color of a star and its brightness, also called absolute magnitude. The HertzsprungRussell diagram is a plot of the surface temperature (color) of stars vs. their luminosity (brightness).

Luminosity LV GH¿ QHG DV WKH LQWHQVLW\ RU EULJKWQHVV RI OLJKW IURP D FHOHVWLDO ERG\ ZKLFK FDQ EH XVHG WR LGHQWLI\ WKH ERG\¶V FKDUDFWHULVWLFV $ VWDU¶V OXPLQRVLW\ RU EULJKWQHVV LV SORWWHG RQ WKH \ D[LV RI WKH + 5 GLDJUDP /XPLQRVLW\ LV SORWWHG DV HLWKHU D UDWLR FRPSDUHG WR WKH 6XQ ZKLFK ZRXOG XVH FRPSDUDWLYH UDWLRV RQ WKH [ D[LV RU DEVROXWH magnitude, which involves a value greater than or less than zero. (The Sun has a magnitude of about 5 RQ WKH + 5 GLDJUDP 7KLV YDOXH LQWHUSUHWV KRZ EULJKW D VWDU ZRXOG EH LI DOO VWDUV ZHUH WKH VDPH GLVWDQFH from Earth. %ULJKWHU VWDUV DUH IRXQG QHDU WKH WRS RI WKH + 5 GLDJUDP ZKLOH GLPPHU VWDUV DUH IRXQG QHDU WKH ERWWRP of the diagram. Our Sun would be found in the middle of the axis, since the Sun is considered to have a luminosity of 1 and an absolute magnitude of 5.

28 | Life Cycles of Stars

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STEMscopedia -20

Brighter stars

108

-15

106

-10

104

-5

102

0

1

+5

10-2

+10

10-4

+15

10-6

Dimmer stars

Absolute magnitude (brightness)

Luminosity relative to the Sun

1010

+20

7KH + 5 GLDJUDP DOVR VKRZV WKH WHPSHUDWXUHV RI VWDUV 7KH temperature of a star is the average kinetic energy of all the particles in a star. Star temperatures are measured in kelvins. Hotter stars are RQ WKH OHIW RI WKH [ D[LV FORVHU WR WKH RULJLQ ZKLOH FRROHU VWDUV DUH WRZDUG WKH ULJKW 7KLV LV WKH [ D[LV RI WKH + 5 GLDJUDP 1RWH WKDW WKH WHPSHUDWXUH RI D VWDU LQFUHDVHV DV \RX PRYH WRZDUG WKH OHIW QRW WKH right.

Temperature (kelvin) 10,000

30,000

O

B

Hotter stars

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A

6,000

F

G

3,000

K

M

Cooler stars

Life Cycles of Stars | 29

STEMscopedia VWXGLHG 7KLV LV D IXOO + 5 GLDJUDP ZLWK VWDUV SORWWHG RQ LW <RX FDQ VHH WKH PRUH PDVVLYH VWDUV DW WKH WRS of the diagram, and the smaller ones at the bottom.

Betelgeuse

4VQFSHJBOUT Rigel

Antares

-VNJOPTJUZ UIF 4VO

Polestar

Arcturus

(JBOUT .BJO TFRVFODF

The Sun

8IJUF EXBSGT

What patterns do you notice in the stars plotted on the diagram? Probably the most obvious one is the OLQH RI VWDUV WKDW VWUHWFKHV GLDJRQDOO\ DFURVV WKH JULG 7KHVH DUH PDLQ VHTXHQFH VWDUV 7KH\ UDQJH IURP cool and small to hot and big. As they get hotter, they seem to increase in size and get more blue in FRORU $V WKHLU VL]H LQFUHDVHV WKH\ PRYH YHUWLFDOO\ XS WKH \ D[LV RQ WKH GLDJUDP DQG PRUH WRZDUG WKH OHIW RQ WKH [ D[LV DV WKHLU WHPSHUDWXUH LQFUHDVHV +RWWHU EULJKWHU VWDUV DUH LQ WKH XSSHU OHIW FRUQHU ZKLOH dimmer, cooler stars are found on the lower right. Supergiants and giants are cooler and have higher luminosity, so they are found near the upper right of the diagram. White dwarfs, which are hot and small, are toward the lower left of the diagram.

30 | Life Cycles of Stars

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STEMscopedia This tool is very helpful to astronomers who want to learn about the characteristics of a star. $VWURQRPHUV FDQ XVH DQ + 5 GLDJUDP WR GHWHUPLQH WKH FKDUDFWHULVWLFV RI D SDUWLFXODU VWDU RU SUHGLFW KRZ its characteristics could change as it moves through its life cycle.

the s e o d hy 5. W FDWLRQ RI FODVVLŞ only show giant of the r e p u s top ot at the ram, and n iag H-R d he bottom? at t

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Life Cycles of Stars | 31

STEMscopedia Gloria Suzanne Koenigsberger Horowitz National Autonomous University of Mexico (UNAM) Gloria Suzanne Koenigsberger Horowitz is an astronomer specializing in the structure and development RI KLJK PDVV VWDUV SDUWLFXODUO\ WZR VWDU V\VWHPV FDOOHG ELQDU\ VWDUV 6KH LV D SURIHVVRU DQG UHVHDUFK VFLHQWLVW DW 81$0¶V ,QVWLWXWH RI 3K\VLFDO 6FLHQFH 6KH VHUYHG DV GLUHFWRU RI WKH $VWURQRPLFDO ,QVWLWXWH from 1990 to 1998 and helped Mexico establish a connection to the internet in the late 1980s.

Gloria Koenigsberger is a Mexican astrophysicist who studies the development and behavior of stars and has a special interest in binary star systems.

32 | Life Cycles of Stars

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STEMscopedia 7KHUH DUH WZR EDVLF NLQGV RI VWDUV DQG HDFK IROORZV LWV RZQ SDWKZD\ 7KH FODVVL¿ FDWLRQ RI D VWDU GHSHQGV RQ LWV PDVV 7KRVH WKDW DUH VPDOOHU WKDQ WZR WLPHV RXU 6XQ¶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explode in a supernova, leaving either a black hole or a neutron star behind.

7KH +HUW]VSUXQJ 5XVVHOO GLDJUDP FDQ EH XVHG WR SORW WKH UHODWLRQVKLS EHWZHHQ D VWDU¶V EULJKWQHVV DQG temperature, allowing scientists to compare the characteristics of various stars.

Connect It What happens when a star dies?

Depending on its mass, either the star will collapse in on itself, forming a planetary nebula, or if it is large enough, it will undergo an explosion called a supernova and then become a neutron star or black hole.

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Life Cycles of Stars | 33

STEMscopedia 1

A certain star is 17 times the mass of our Sun. It is nearing the end of its life cycle. The star will most likely– A continue conducting nuclear fusion for at least 10 billion years.

B complete its life cycle as a planetary nebula.

C explode in a supernova, leaving behind a white dwarf or black hole.

D fuse carbon into hydrogen and helium.

2

A star has begun to fuse hydrogen into helium, and will remain in its current life stage for about 90% of its life cycle. It is most likely– A D PDLQ VHTXHQFH VWDU B a supergiant.

C a white dwarf.

D a planetary nebula.

3

$ ORZ PDVV VWDU ZLOO IXVH LWV K\GURJHQ LQWR KHOLXP EHFRPH D JLDQW DQG WKHQ ZLOO OLNHO\± A become a planetary nebula and contribute to the formation of new stars.

B form a new protostar.

C become a supernova and then a white dwarf.

D become a planetary nebula and exert gravitational force on nearby objects.

34 | Life Cycles of Stars

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STEMscopedia Hertzsprung-Russell (H-R) Diagram Blue

Luminosity/brightness (compared to the Sun)

O

B

Bluewhite

White

A

F

Yellowwhite Orange

G

K

Red

Color

M

Spectral classification Betelgeuse

10,000 Supergiants 100 Main sequence stars

Sun

Giants

1

0.01 White dwarfs 0.0001 40,000

20,000 10,000 5,000 Temperature (K)

2,500

4

:KLFK RI WKH IROORZLQJ VWDWHPHQWV DSSHDUV WR EH WUXH DFFRUGLQJ WR WKH SDWWHUQV LQ WKH + 5 GLDJUDP" A Smaller, cooler stars are more luminous than those with more mass and higher temperatures.

B Stars that are smaller and cooler are not as luminous as those with more mass and hotter temperatures.

C Stars closer to Earth tend to have higher temperatures.

D White dwarfs are only found between temperatures of 10,000 and 7,000 kelvins.

5

:KLFK RI WKH IROORZLQJ GHVFULSWLRQV DFFXUDWHO\ GLVFXVVHV D FKDUDFWHULVWLF RI WKH VWDU %HWHOJHXVH" A It has a luminosity less than that of the Sun. B It is warmer than the Sun. C It is younger than the Sun. D It is cooler and more massive than the Sun.

6

Describe what it means to say that humans are made of the same stuff as stars.

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Life Cycles of Stars | 35

Celestial Objects

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37

STEMscopedia Imagine lying on the cool grass and gazing at the stars on a summer night. Astronomers have been studying the sky like this for centuries. Stargazing by scientists led to various theories about the arrangement and orbits of objects such as Earth, the Moon, and the Sun. Many cultures have tried to explain the movements of celestial bodies through legends and tales that they developed while watching these movements throughout their lifetimes.

The earliest astronomers thought Earth was the center of the universe. This is known as the geocentric theory. The reasoning behind the geocentric theory was that Earth had to be the center of the solar system because all things fall to the surface of the planet. This included objects that originated in space.

In addition, because people are unable to feel Earth move, it was assumed the rest of the solar system was moving around Earth.

Later, in the third century BCE, Aristarchus of Samos suggested that the Sun was the center of the universe, which is known as the heliocentric theory. The idea was not pursued until about the 1600s, when Nicolaus Copernicus investigated the idea. Using his ideas, astronomers like Johannes Kepler, Tycho Brahe, and others were able to determine that the Sun is not the center of the universe, but it is the center of the solar system.

What about the other objects in the solar system? Do all of the planets, moons, and other objects have predictable orbits around the Sun?

All of the solar system’s objects have physical properties that set them apart from others. Let’s look at the locations, movements, and physical properties of these objects.

zing a g r a t did s e 1. How some of th t lead to ideas abou t earlies vements of o the m l objects in iaa celest r system? la our so

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Celestial Objects | 39

STEMscopedia As you know, the Sun is the center of the solar system. It is a medium-sized main sequence star measuring about 109 times the diameter of Earth, located about 93 million miles from Earth. Like other stars, the Sun contains large amounts of hydrogen and helium. Hydrogen fuses into helium through the process of nuclear fusion. This dynamic nature of the Sun is of great value to Earth, as the fusion process releases the light and heat on which Earth depends.

The Sun contains about 85% of the solar system’s mass. It also has the largest gravitational pull on the other bodies around it. This means that although any planet or moon in the solar system has gravity, the Sun has the most. This is why everything else in the solar system revolves around, or orbits, the Sun. Although other planets are smaller, like the smallest planet, Mercury, they all exert a gravitational force on nearby objects.

lanet p h ic 2. Wh e least has th al pull on tion gravita jects iin the ob other stem? y s r sola

40 | Celestial Objects

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STEMscopedia made of gas, its speed differs at different locations. It rotates faster at the equator than at the poles. We have evidence of this rotation from seeing sunspots and other features move across the Sun’s surface.

7HOHVFRSHV ZLWK VRODU ¿ OWHUV DOORZ XV WR ORRN DW WKH VXUIDFH RI WKH 6XQ DQG VHH VXQVSRWV 7KH 6XQ DQG WKH entire solar system also revolve around the center of the Milky Way galaxy.

Although the Sun is made of gas, it is composed of layers that vary in temperature. The Sun’s core is hotter than its outer layers. Hot plasma rises from the core toward the surface, where it cools and sinks back toward the core. This process of convection is ongoing.

6RODU À DUHV RFFXU DV LQWHQVH EXUVWV RI UDGLDWLRQ ZKHQ PDJQHWLF HQHUJ\ LV UHOHDVHG IURP WKH 6XQ 7KHVH explosive events, which are the largest explosions within our solar system, can last from a few minutes WR VHYHUDO KRXUV DQG UHOHDVH HQHUJ\ LQWR VSDFH 1RW DV VWURQJ DV D VRODU À DUH D VRODU SURPLQHQFH UHPDLQV LQ WKH 6XQ¶V PDJQHWLF ¿ HOG ZKLOH D À DUH HVFDSHV WKH 6XQ¶V SXOO DQG VFDWWHUV ZDYHV RI HQHUJ\ across the galaxy.

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Celestial Objects | 41

STEMscopedia The eight planets that orbit the Sun are the other major components of the solar system. They are made of the same elements as Earth, and in roughly the same proportions, leading scientists to believe that all eight are about the same age as the Sun, about 4.6 billion years, because all objects in our solar system formed from the same cloud of dust and gas.

The eight planets are separated into groups based on whether they are inside or outside of the asteroid belt. The rocky, terrestrial inner planets of Mercury, Venus, Earth, and Mars are smaller than the gas giants located outside of the asteroid belt. The gas giants are Jupiter, Saturn, Uranus, and Neptune.

Almost all of the planets have atmospheres, but Earth is the only one that has a breathable mix of gases.

The four inner planets vary in size, temperature, and atmosphere. Mercury, the closest to the Sun, is the smallest of the rocky planets. It has no atmosphere and has extreme hot and cold temperatures because it rotates so slowly. Venus is similar in size to Earth but has a much hotter and denser atmosphere than Earth. Mars is the furthest of the rocky planets from the Sun. Mars has a very thin atmosphere and is much colder than Earth.

42 | Celestial Objects

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STEMscopedia All of the planets have a central axis around which they rotate. The period of that rotation is the day length of the planet. On Earth, it takes any location on the planet roughly 24 hours to rotate and return to the same place, so this is the length of an Earth day/night cycle. Jupiter has the fastest rotation speed at 45,583 kilometers per hour, taking 9 hours 55 minutes to complete one rotation. Venus has the slowest, taking 243 days 6 minutes to complete a rotation at only 6.5 kilometers per hour. Most of the planets spin in the same direction as Earth, from west to east. The exceptions are Venus and Uranus, which rotate the opposite way, from east to west.

think u o y o d 3. How s on Earth n conditio e different b would th rotated if Ear t to west, as from e ite of its oppos irection? t d curren

While each of the planets is rotating on its axis, each one is also revolving around the Sun, like cars on a racetrack. The time it takes for a planet to complete its revolution is called its year.

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Celestial Objects | 43

STEMscopedia Moons are celestial bodies that revolve around planets. The inner planets have a total of three moons, with Earth having one and Mars having two. Mercury and Venus do not have any of these natural satellites, likely because of their smaller mass, weaker gravity, and the locations where they formed in the early solar system.

The outer planets have many more moons! Jupiter has 67, while Saturn has 62. Uranus has 27, and Neptune has 14. A few of these moons have their own atmospheres, such as Titan, a moon orbiting Jupiter.

Moons in our solar system are all very different. They come in a variety of sizes, shapes, and types.

Some have atmospheres. Some have liquid oceans under their surfaces. Some orbit their planets fast, and others slow. All of the moons have lower average temperatures than Earth.

Our moon revolves around Earth and slowly moves eastward, rising later each day and passing through LWV SKDVHV QHZ ¿ UVW TXDUWHU IXOO ODVW TXDUWHU DQG QHZ DJDLQ 7KH 0RRQ¶V DSSDUHQW SKDVHV DUH FDXVHG by changes in what we see from Earth as various parts of the Moon are illuminated by the Sun.

Our view from Earth changes depending on the Moon’s position as it is illuminated by the Sun during its revolution around Earth each month.

44 | Celestial Objects

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STEMscopedia Moon is pockmarked with craters from impacts over billions of years and lacks an atmosphere to protect LW ,W GRHV QRW SURGXFH LWV RZQ OLJKW EXW UHÀ HFWV WKH 6XQ¶V OLJKW 6FLHQWLVWV WKLQN WKH 0RRQ IRUPHG DIWHU DQ object collided with Earth and sent some of the material into space, which later came together to form the Moon.

When Earth, the Moon, and the Sun are lined up in the right positions, we see eclipses from Earth.

There are two types of eclipses. A lunar eclipse occurs when Earth is positioned between the Sun and the Moon. Earth’s shadow covers the Moon. A solar eclipse occurs when the Moon is positioned just right between Earth and the Sun. The Sun appears to be covered by the Moon either partially or completely.

Solar eclipses happen regularly but are not visible to most of Earth’s population.

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Celestial Objects | 45

STEMscopedia $ PHWHRURLG E\ GH¿ QLWLRQ LV VPDOOHU WKDQ DQ DVWHURLG EXW ELJJHU WKDQ DQ DWRP 0HWHRURLGV DUH PDGH RI VLOLFDWH PLQHUDOV DQG OLJKWHU PHWDOV OLNH QLFNHO DQG LURQ 7KH\ FDQ EH IRXQG À RDWLQJ LQ VSDFH EHWZHHQ planets, in the atmosphere, and on the ground. If a meteoroid enters Earth’s atmosphere and begins burning up due to friction, it glows and is called a meteor, also known as a shooting star. Some shooting stars hit the ground and are known as meteorites.

Meteor showers happen several times a year and result when Earth’s orbit takes it through a cloud of dust. The dust particles entering Earth’s atmosphere glow as they burn, creating the fast-moving, wellnamed shooting stars. Some of those meteors are only millimeters wide!

Asteroids are basically bigger meteoroids. They can be made of the same materials as meteoroids, but most of these are in a concentrated ring between Mars and Jupiter, revolving with the planets around the Sun. Some occasionally travel closer to Earth if their orbits are disturbed.

Scientists estimate that Earth has been hit hundreds of times by asteroids; currently, there are about 175 impact craters from such impacts. One of the most famous is the impact that created the Gulf of Mexico; this impact is the one thought to have caused the extinction of the dinosaurs. Overall, these events are rare, and scientists estimate that an object with a length of about 100 meters hits Earth about once every 5,000 years. Smaller ones come into our atmosphere much more often.

46 | Celestial Objects

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STEMscopedia planets. They revolve around the Sun just as planets do, but they tumble as they do so.

Asteroids are rocky bodies that do not have atmospheres. They range from a few meters to hundreds of kilometers wide. Iron and nickel are the most common elements found in asteroids. They are pitted or cratered, and most are irregularly shaped. A few are even spherical!

Vesta is the largest asteroid currently known.

Comets are the other small celestial bodies in our solar system that orbit the Sun. They are made of ice, dust, and rock. Comets have four main parts: a nucleus, a coma, an ion tail, and a dust tail. The nucleus is the spherical part of the comet at the front, while the coma is the halo-shaped cloud surrounding the nucleus. The ion tail and the dust tail are what make the long trailing shape behind the nucleus. The tail always faces away from the Sun. These celestial bodies have long, elliptical orbits around the Sun. Many comets, such as Halley’s comet, are thought to have originated in the areas beyond Neptune, known as the Kuiper Belt and the Oort cloud.

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Celestial Objects | 47

STEMscopedia The Kuiper Belt is a large doughnut-shaped region consisting of millions of frozen objects outside of Neptune’s orbit that may be left over from the solar system’s early formation. It begins about 30 au (astronomical units) from the Sun, or 30 times the distance from the Sun to Earth. The main region extends to 50 au, and the outer region is much larger, ending around 1,000 au. The movements RI REMHFWV LQ WKH .XLSHU %HOW DUH WKRXJKW WR EH LQÀ XHQFHG E\ WKH JUDYLW\ RI WKH PDLQ HLJKW SODQHWV especially Neptune. Objects within the belt probably consist of water, ice, and compounds like ammonia and methane. Interestingly, as large as the area is, all of the mass of the Kuiper Belt is thought to be about one-tenth the mass of Earth.

48 | Celestial Objects

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STEMscopedia Oort cloud, located on the edge of the solar system. It may extend one-quarter to one-half the distance from our Sun to the next star and likely contains millions of objects. Scientists have not seen any objects in the Oort cloud so far but think there may be many asteroids or huge ice chunks within its depths. The overall movement of the Oort cloud is unknown.

of kinds e t a h 5. W are in th objects Belt and Kuipper cloud?

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Celestial Objects | 49

STEMscopedia Amy Mainzer University of Arizona and NASA’s Near-Earth Object Wide-Field Infrared Survey Explorer Professor Amy Mainzer is an American astronomer who studies asteroids and potential threats to Earth by cataloging asteroids and comets, collecting data on sizes, orbits, and other characteristics of these objects. She leads the largest asteroid-hunting project in history in her job as principal investigator of NASA’s Near-Earth Object Wide-Field Infrared Survey Explorer (NEOWISE) telescope mission, which surveys the asteroids near us, including those that are potential hazards to our planet. She received NASA’s Exceptional Public Service medal for her work on near-Earth asteroids in 2018 and even has an asteroid named after her, Asteroid 234750 Amymainzer.

An asteroid like the ones studied by NASA’s Near-Earth Object Wide-Field Infrared Survey Explorer (NEOWISE) telescope mission

50 | Celestial Objects

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STEMscopedia The Sun is the center of the solar system. It is a medium-sized main sequence star measuring about 109 times the diameter of Earth and is located about 93 million miles from Earth. The eight planets are separated into groups based on whether they are inside or outside of the asteroid belt. The rocky, terrestrial inner planets are smaller than the gas giants located outside of the asteroid belt. While each of the planets is rotating on its axis, it is also revolving around the Sun. Meteoroids are made of silicate minerals and lighter metals like nickel and iron. Asteroids are basically bigger meteoroids. They can be made of the same materials as meteoroids, but most of these are in a concentrated ring between Mars and Jupiter. Comets, on the other hand, originate from the Oort cloud and travel in elliptical orbits that may bring them close to Earth. The Kuiper Belt has millions of frozen objects outside of Neptune’s orbit that may be left over from the solar system’s early formation. It is surrounded by the spherical Oort cloud.

Connect It How can we predict the movements of bodies in our solar system?

7KH PRYHPHQWV RI WKH REMHFWV ZH VHH LQ WKH VN\ DUH LQÀ XHQFHG E\ WKHLU PRYHPHQWV DV ZHOO DV (DUWK¶V For hundreds of years, scientists and nonscientists have been trying to unravel the mysteries of the objects in the sky. We now know that these movements are affected by gravity and usually follow predictable paths, allowing us to create calendars, predict the visibility of comets, and gauge the threat level of near-Earth objects.

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Celestial Objects | 51

STEMscopedia 7KHUH DUH ¿ YH FODVVHV RI VRODU À DUHV GHSHQGLQJ RQ WKH VWUHQJWK DQG LQWHQVLW\ RI WKH ; UD\V HPLWWHG 7KH WKUHH ORZHVW LQWHQVLWLHV FDOOHG $ % DQG & FODVV VRODU À DUHV GR QRW FDXVH LVVXHV IRU XV RQ (DUWK 7KH WZR ODUJHVW LQWHQVLWLHV FDOOHG ; DQG 0 FODVV VRODU À DUHV FDQ LPSDFW (DUWK¶V VDWHOOLWHV DQG DVWURQDXWV LQ VSDFH 7KHVH VRODU À DUHV FDQ FDXVH GDPDJH RU HYHQ PDNH VDWHOOLWHV XQXVDEOH 7KH VWURQJHVW VRODU À DUHV PD\ WULJJHU FRURQDO PDVV HMHFWLRQV WKDW UHOHDVH SODVPD DQG D PDJQHWLF ¿ HOG IURP WKH 6XQ 7KHVH can disrupt Earth’s magnetosphere, causing electrical blackouts of areas in their direct paths. This can also cause radio blackouts of certain radio frequencies. Because of the potential impacts, many organizations like NASA and NOAA monitor the Sun closely.

Summarize It 1

Which of the following statements is NOT true about planets?

A Planets have two main movements: a rotation around an axis and a revolution around the Sun. B Many of the planets in our solar system have atmospheres.

C The outer planets as a group have more moons than the inner planets.

D All planets have at least one moon.

2

Which statement is true about the Kuiper Belt and Oort cloud?

A The Kuiper Belt is a doughnut-shaped area surrounded by the spherical Oort cloud; both likely contain thousands of icy objects.

B The Oort cloud is surrounded by the Kuiper Belt; both contain asteroids.

C Scientists have studied both the Kuiper Belt and Oort cloud extensively.

D Objects in the Kuiper Belt and Oort cloud are only affected by the gravity of nearby Neptune.

3

Where is the asteroid belt located?

A Between Saturn and Uranus B Between Mars and Jupiter C Outside of Neptune’s orbit D Surrounding the Kuiper Belt

4

Fill in the table to describe the movements of Earth.

Movement

Description

Time Period One of these takes approximately 365 ________

Rotation

52 | Celestial Objects

One of these takes approximately ___________

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STEMscopedia Which celestial object has a nucleus surrounded by a cloud and a tail that faces away from the Sun? A An asteroid B A meteoroid C A comet D A moon 6

Describe the Sun, meteors, and asteroids in terms of their physical properties, locations, and movements.

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Celestial Objects | 53

Gravity

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55

STEMscopedia Have you ever thought about how gravity works? What factors make it stronger or weaker? Gravity controls the movements of every object in our solar system, including tiny objects such as comets and asteroids. But comets orbit the entire solar system, while most asteroids stay between Mars and Jupiter.

What causes the difference in the movements of these celestial bodies?

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Gravity | 57

STEMscopedia Scientist Isaac Newton made the concept of gravity a household word. Gravity is the invisible force of attraction between objects with mass. Newton’s law of universal gravitation states that every object in the universe attracts every other object and that the force is affected by mass and distance.

Mass is the measure of how much matter is in an object or substance. All objects have mass, regardless of whether it is a small or large amount. Because of this, all objects will pull other objects with mass toward them. Gravity is responsible for the formation of planets, stars, and solar systems all throughout the universe. It is the force that governs the motions of the planets, moons, comets, asteroids, and other objects in the solar system and throughout the universe. A force is a push or pull that can change the motion of an object.

Gravity is an attractive force that works on any object, including astronauts and equipment in space.

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58 | Gravity

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STEMscopedia Objects in our solar system are constantly in motion. Motion is the change in an object’s position with respect to time and in comparison with the position of other objects used as reference points. Motion happens in many places in our daily lives—from the blood that moves in our bodies to Earth rotating and revolving as it orbits the Sun. There are four basic types of motion: reciprocating, oscillating, circular, and linear. Planets exhibit circular motion as they revolve around the Sun in a curved path we call an orbit. An orbit is a curved path followed by a satellite as it revolves around an object.

What causes a planet to orbit the Sun? Planets are moving forward in the universe, but the Sun’s mass, which equals about 99% of the total mass of the solar system, means that it exerts a tremendous force of gravitational attraction on bodies in the solar system. So, a planet’s forward motion, combined with the Sun’s gravity pulling the body toward it, creates the curved path formed by the object as it orbits the Sun. Asteroids in the solar system are also subject to this attractive force. It is thought that asteroids are remnants of planetesimals, or precursors to protoplanets. They never accreted into planets because Jupiter’s gravity prevented them from doing so. Their forward motion, combined with the force of the Sun’s gravity, keeps them in their current orbits, in a band between Mars and Jupiter.

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Gravity | 59

STEMscopedia Objects in Our Solar System Gravity is responsible for the revolutions of planets around the Sun and moons around planets. A revolution is the movement of one object around a center or another object.

7KH FRQFHSW RI UHYROXWLRQ KHOSV XV GH¿ QH WKH REMHFWV WKDW PDNH XS RXU VRODU V\VWHP 7KH solar system consists of a star and the group of planets and other celestial bodies that are held by its gravitational attraction and revolve around it. Without gravity, objects such as moons would likely move in straight lines, increasing the distance between themselves and the Sun instead of maintaining fairly regular orbits.

This is a diagram of the eight planets in the solar system showing the moons that also orbit each planet.

The more mass a celestial body has, the stronger force of gravity it will exert. For instance, the Sun has WKH ODUJHVW LQÀ XHQFH RI JUDYLW\ RQ DQ\ RWKHU ERG\ LQ WKH VRODU V\VWHP E\ IDU 7KH ERG\ ZLWK WKH VHFRQG VWURQJHVW LQÀ XHQFH RI JUDYLW\ LV DOVR WKH RQH ZLWK WKH KLJKHVW PDVV DIWHU WKH 6XQ²WKH SODQHW -XSLWHU Jupiter’s mass is the equivalent of about 318 Earths, but it has just 2.4 times Earth’s gravity.

60 | Gravity

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STEMscopedia will be attracted. Smaller objects will exert less of a gravitational force on each other.

Mass has an effect on the strength of an object’s gravitational attraction. Objects with more mass will exert a stronger force than those having less mass.

Gravity affects weight. A person weighing 100 pounds on Earth would weigh 2.4 times that, or 240 pounds, on Jupiter. In contrast, the same person would weigh about 38 pounds on Mars, since the force of gravity is much less on the small planet.

The distance between objects also affects the pull of gravity. Distance is a measure of how far apart two objects are. Earth is closer to us, so it has more of a pull on our bodies than Jupiter. This is true even though Jupiter is larger than Earth. The Moon orbits Earth for the same reason—since Earth is closer to the Moon than the Sun is, the Moon orbits Earth instead of the Sun. Objects that have less distance have a greater gravitational pull. Objects with a greater distance from each other have a lesser gravitational pull.

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Gravity | 61

STEMscopedia Nergis Mavalvala Massachusetts Institute of Technology Astrophysicist Nergis Mavalvala is the dean of MIT’s School of Science. A Pakistani-American, she has made groundbreaking discoveries in the area of gravitational wave detection. She is a leading member of the Laser Interferometer Gravitational-Wave Observatory. This observatory features a piece of VFLHQWL¿ F HTXLSPHQW WKDW PDGH WKH ¿ UVW GLUHFW GHWHFWLRQ RI WKH ULSSOHV LQ WKH IDEULF RI VSDFH WLPH NQRZQ as gravitational waves. The work to which she contributed was awarded the Nobel Prize in Physics in 2017.

She has studied black holes and Cosmic Microwave Background (CMB), which may provide evidence for the Big Bang.

62 | Gravity

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STEMscopedia Gravity is the invisible force of attraction between two objects with mass. It acts on any object with mass and governs the motion of the objects in the solar system. Gravity is responsible for the revolutions of planets around the Sun and moons around planets. A revolution is the movement of one object around a center or another object. Mass and distance control gravitational pull. The larger the mass of two objects, the more strongly they will be attracted. Smaller objects will exert less of a gravitational force on each other. Objects that have less distance have a greater gravitational pull.

Objects with a greater distance from each other have a lesser gravitational pull.

Connect It What keeps asteroids in the asteroid belt in orbit?

The asteroids’ forward motion, combined with the gravitational force of the Sun, keeps them in their current orbits between Mars and Jupiter.

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Gravity | 63

STEMscopedia Summarize It 1

:KLFK WZR IDFWRUV FRQWURO WKH LQÀ XHQFH RI JUDYLW\ RQ REMHFWV" A Mass and distance B Distance and distribution C Planetary radius and mass D Distribution and location in the solar system

2

Which statement is true about gravity in our solar system?

A It changes along with an object’s mass depending on its location in the solar system.

B It governs the movements of objects in the solar system inside the asteroid belt.

C It is the reason that comets have orbits spanning millions of miles.

D It is the force that governs the motion of every object in the solar system.

3

The Sun is expected to complete its life cycle in about 5 billion years. One step in the Sun’s life cycle involves the Sun shrinking into a white dwarf. How will this drastic decrease in mass affect its gravitational pull on the planets if their orbits are the same at that time as they are today?

A The decreased mass will increase gravitational pull on the outer planets.

B The increased mass will decrease gravitational pull on the outer planets.

C The decreased mass will decrease the gravitational pull on the outer planets.

D The change in mass will not make a difference for gravitational force.

4

Describe how gravity governs the motion of our solar system.

64 | Gravity

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Characteristics and Use of the Electromagnetic Spectrum

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65

STEMscopedia Life on Earth is highly dependent on light. Plants need light for energy to perform photosynthesis.

Animals need plants for oxygen and food. Animals also need light to see. Have you ever stopped to think about what light actually is?

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Characteristics and Use of the Electromagnetic Spectrum | 67

STEMscopedia The light we see on Earth is a type of electromagnetic radiation. Radiation refers to energy that spreads out as it travels. Electromagnetic radiation is energy made up of special particles called photons. Light energy travels faster than anything else in the known universe: approximately 800,000,000 meters per second (m/s).

Electromagnetic waves are not the same as mechanical waves because they do not require matter.

They can travel through air, water, and solid material, but they can also travel through space, which has no matter in it. When we talk about light or electromagnetic energy, we are using two names for the same idea.

68 | Characteristics and Use of the Electromagnetic Spectrum

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STEMscopedia There are many different types of electromagnetic radiation, but all travel as waves. Scientists use wavelengths to classify electromagnetic waves. Wavelength is a measurement of the length of a single wave of energy. Wavelength can be measured from crest to crest, trough to trough, or any pair of points that are the same on a wave.

Wavelength

Crest

Trough electromagnetic spectrum.

The electromagnetic spectrum includes radio waves, microwaves, infrared waves, visible light, ultraviolet waves, X-rays, and gamma rays. The electromagnetic spectrum is usually organized with the different types of radiation arranged in order of longest wavelength to shortest.

Regardless of their wavelengths, all types of electromagnetic radiation travel at the same speed of about 300,000,000 m/s (meters per second). In addition to wave speed and wavelength, electromagnetic waves can be measured by frequency. Frequency refers to the number of waves that pass a given point in a given period of time (usually one second). Electromagnetic waves with longer wavelengths have lower frequencies; in other words, fewer waves pass a given point each second. Electromagnetic waves with shorter wavelengths have higher frequencies, which means more waves pass a given point each second. Take a moment to look at the different types of waves based on common uses, wavelengths, and frequencies.

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Characteristics and Use of the Electromagnetic Spectrum | 69

STEMscopedia

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70 | Characteristics and Use of the Electromagnetic Spectrum

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STEMscopedia In the middle of the spectrum are visible light waves. Visible light allows us to see objects with our eyes.

Objects must give off light in the visible range for us to be able to see it. In fact, human eyes give off light, but it cannot be seen because it is not in the visible spectrum! Plants can capture chemical energy in visible light and use it to conduct photosynthesis. Bees can use the unique behavior of visible light in the atmosphere to navigate. You need visible light to see, but did you know you use other parts of the electromagnetic spectrum in your everyday life? Are all types safe?

Every time you use a cell phone or listen to the radio, you are using radio waves. Radio waves can travel through the air to transmit information such as music or a conversation. Radio waves are harmless WR WKH KXPDQ ERG\ DQG FDQ EH UHÀ HFWHG WR WUDQVPLW LQ GLIIHUHQW GLUHFWLRQV ,QIRUPDWLRQ LV VHQW ZLWKLQ the wave and decoded by radios and television equipment. GPS, global positioning systems, also use radio waves.

GPS technology uses radio waves to identify and report locations.

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Characteristics and Use of the Electromagnetic Spectrum | 71

STEMscopedia up your food. This energy heats up cold food. Microwaves are also used in communications to and from spacecraft. These waves have higher energy than radio waves because of their shorter wavelength.

This additional energy allows the waves to pass through the atmosphere. Microwaves and radio waves together allow us to detect differences in weather via radar, so they are valuable to meteorologists in tracking precipitation and developing weather forecasts. Microwaves can also help extend TV signals over greater distances.

Infrared waves have longer wavelengths than visible light but shorter than microwaves. All of Earth’s energy that is given off into space is in this area of the spectrum. All objects give off infrared light, but the human eye cannot perceive it. Infrared light is associated with heat. Infrared waves show us the characteristics of stars in space as well as areas of star formation that would otherwise be hidden from DVWURQRPHUV ,QIUDUHG ZDYHV DUH XVHG LQ ¿ EHU RSWLF FDEOHV WKDW SURYLGH FRPPXQLFDWLRQ VHUYLFHV WR homes and businesses. The remote control you use to play video games or change settings on your TV uses infrared to carry out commands. Infrared imaging technology is frequently used to help engineers, contractors, and architects detect areas of heat loss in a structure. Warmer areas of a structure show up in shades of red, orange, and yellow, while colder areas are blue.

72 | Characteristics and Use of the Electromagnetic Spectrum

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STEMscopedia he ribe t en c s e D 3. betwe ip h s n relaatio length and wave in the y g r ene gnetic a m o r t . elec waves m u r t spec

Higher frequencies of electromagnetic waves can damage the body, and ultraviolet waves are one example. The Sun emits huge amounts of ultraviolet waves in addition to visible light, but our DWPRVSKHUH ¿ OWHUV PXFK RI WKRVH RXW :KHQ \RX JHW D VXQEXUQ LW LV EHFDXVH RI XOWUDYLROHW 89 UDGLDWLRQ JLYHQ RII E\ WKH 6XQ 7KH 89 UD\V FDQ GHVWUR\ VNLQ FHOOV FDXVLQJ SDLQIXO EOLVWHUV DQG LQ VRPH FDVHV cancer. However, since these waves can kill bacteria and microorganisms, they are useful in sterilizing objects such as medical instruments. We also use these waves to study objects in the universe.

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Characteristics and Use of the Electromagnetic Spectrum | 73

STEMscopedia have the ability to break down strands of DNA and thus can be dangerous to humans. They are also useful, though, in medicine and in astronomy. When you get a CT scan or an X-ray, you are using X-rays. Airport security kiosks also use this type of wave.

Hazards of radiation in different parts of the electromagnetic spectrum depend on the radiation’s wavelength and frequency. Too much time exposed to certain types of electromagnetic radiation can be damaging. The radiation is likely to cause more damage to the human body if the frequency is higher.

Gamma rays DUH SURGXFHG E\ VXSHUQRYDV VRODU À DUHV WKXQGHUVWRUPV DQG WKH GHVWUXFWLRQ RI DWRPV These tiny waves have a tremendous amount of energy and are thus a huge threat to life. Too much exposure to gamma rays can damage cells, causing mutations (which may lead to cancer), and cell death. Like all waves, even gamma rays are useful. They are used in radiotherapy for cancer treatment and diagnostic work and in plumbing for pipe-leakage detection.

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Humans cannot directly perceive any part of the electromagnetic spectrum other than visible light. The visible spectrum is a small part of the complete electromagnetic spectrum, with wavelengths ranging from 380 to 740 nm. Humans perceive differences in wavelength as different colors. Most of what we know about the universe and the objects in it comes from the study of visible light. Do you think scientists can use the rest of the electromagnetic spectrum to study the universe? If so, how do you think this is possible?

74 | Characteristics and Use of the Electromagnetic Spectrum

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STEMscopedia Most of our knowledge about the universe comes from observations of visible light. For example, scientists have discovered the composition of many objects in the universe—including distant stars— VLPSO\ E\ DQDO\]LQJ WKH YLVLEOH OLJKW WKHVH REMHFWV HPLW RU UHÀHFW 6FLHQWLVWV KDYH GRQH H[SHULPHQWV to determine the colors given off by different elements when they are burned. By studying the colors given off by a star, scientists can determine which elements make up that star. Sometimes, we can look directly at an object with our eyes. Sometimes, we must use telescopes to aid our eyes. At other times, a more complex analysis is required.

Do you think satellite images are photographs? This is a common mistake; satellite images and photographs are quite different. Satellites orbit Earth and use remote sensing to collect digital information. They send digital information to Earth, and people convert this information to images using computers. The process of gathering information about a place or an object without touching it is called UHPRWH VHQVLQJ 7KLV LV GRQH ZLWK UHÀHFWHG RU HPLWWHG HOHFWURPDJQHWLF ZDYHV

Remote sensing instruments are essential for studying the far reaches of the universe. Many objects are too distant or dim to detect with visible light, but these objects also give off low-energy forms of electromagnetic radiation like radio waves, microwaves, and infrared radiation. Special telescopes can pick up these waves from across the universe, allowing scientists to discover distant objects that are impossible to detect through higher-energy waves. Some of these objects are hidden by dust in space.

Others are too cool to emit higher-energy waves. Scientists can use large radio telescopes, similar in appearance to large satellite dishes, to detect radio waves from space. These radio telescopes are located on Earth’s surface, but they allow us to study distant stars that would otherwise be invisible.

Because all objects give off infrared radiation in the form of heat, infrared waves are particularly useful for detecting cooler objects. Special infrared cameras can even be used to detect objects on Earth’s surface. © Accelerate Learning Inc. – All Rights Reserved

Characteristics and Use of the Electromagnetic Spectrum | 75

STEMscopedia

Hotter, more energetic objects and events in the universe give off high-energy radiation with wavelengths that are shorter than those of the visible light spectrum. These include ultraviolet radiation, ; UD\V DQG JDPPD UD\V 8OWUDYLROHW UDGLDWLRQ FDQ EH XVHG WR VWXG\ YHU\ KRW DUHDV RI WKH XQLYHUVH such as the centers of some galaxies where many stars are clustered together. X-rays are given off by extremely hot gases, so they can be used to study events that are even hotter and more energetic than burning stars. These include supernova explosions caused by the deaths of old stars. Gamma rays have the shortest wavelengths, highest frequencies, and highest energies of the entire electromagnetic VSHFWUXP %XUVWV RI HQHUJ\ IURP WKH 6XQ FDOOHG VRODU ÀDUHV JHQHUDWH JDPPD UD\V DV GR RWKHU KLJK energy events in the universe. High-energy processes on Earth, such as nuclear power generation, can also emit gamma radiation.

76 | Characteristics and Use of the Electromagnetic Spectrum

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STEMscopedia

There are two different ways to detect electromagnetic energy: electronically or photographically. In remote sensing, the difference between images and photographs is that images refer to any pictorial representation without paying attention to the wavelengths or remote sensing device used. In contrast, SKRWRJUDSKV DUH GHWHFWHG DQG UHFRUGHG RQ SKRWRJUDSKLF ¿ OP

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Characteristics and Use of the Electromagnetic Spectrum | 77

STEMscopedia Luis Alvarez Los Alamos Laboratory Dr. Luis Alvarez was an experimental physicist, inventor, and professor who won the Nobel Prize in Physics for a piece of equipment developed to investigate particle physics. +H EHJDQ KLV FDUHHU ZRUNLQJ LQ WKH ¿ HOGV RI RSWLFV DQG FRVPLF UD\V +H IRFXVHG PXFK RI KLV UHVHDUFK on nuclear physics. During World War II, he oversaw three important radar systems—one that used microwaves, the Eagle high altitude bombing system, and a system that helped aircraft to perform safe blind landings. He led the construction of the proton linear accelerator.

He used balloons and superconducting magnets to study cosmic rays. Because of his understanding of KRZ HOHFWURPDJQHWLF ZDYHV FDQ EH XVHG LQ VFLHQWL¿ F DSSOLFDWLRQV KH ZDV DVNHG WR KHOS [ UD\ WKH *UHDW 3\UDPLGV LQ (J\SW WR ¿ QG SUHYLRXVO\ XQGLVFRYHUHG FKDPEHUV $ORQJ ZLWK KLV VRQ KH DOVR GHYHORSHG WKH Alvarez hypothesis, which states that a meteoric impact killed the dinosaurs.

Electromagnetic waves helped discover hidden chambers inside the Great Pyramids of Egypt.

78 | Characteristics and Use of the Electromagnetic Spectrum

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STEMscopedia (OHFWURPDJQHWLF ZDYHV FRQVLVW RI YLEUDWLRQV LQ HOHFWURPDJQHWLF ¿ HOGV WKDW FDUU\ SDFNHWV RI HQHUJ\ through mediums and through empty space. The largest waves, radio waves, have the lowest energy. At the opposite end of the spectrum, gamma rays are extremely small but have high energy. This makes different types of waves useful in different applications such as radiation therapy, wireless technologies, ¿ EHU RSWLFV PLFURZDYHV XOWUDYLROHW VWHULOL]DWLRQ DVWURQRPLFDO REVHUYDWLRQV DQG ; UD\V

Connect It Where does light come from? How does it move from place to place?

Life on Earth depends on the light we receive from the Sun for both energy and heat. Light travels through space as part of the electromagnetic spectrum. When light reaches Earth, some makes it to the VXUIDFH DQG VRPH LV UHÀ HFWHG RU ¿ OWHUHG RXW E\ WKH DWPRVSKHUH :KLOH WKH RQO\ SDUW RI OLJKW ZH FDQ VHH is in the visible spectrum, there are many different categories of light that each present their own uses and hazards. We use all the different types to study not only Earth, but the universe.

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Characteristics and Use of the Electromagnetic Spectrum | 79

STEMscopedia Summarize It 1

The electromagnetic spectrum is arranged in order of _____________ and _____________.

2

Wireless communications such as cellular phones use– A radio waves.

B ultraviolet waves.

C gamma waves.

D infrared waves.

3

Infrared waves are used– A to help locate and study objects in the universe far away from Earth.

B in TV remotes and to help people determine areas of high and low heat.

C to clean and sterilize medical instruments.

D to treat medical conditions such as cancer.

4

Meteorologists use _____________ and _____________ waves to monitor the weather and create weather forecasts.

5

Which statement correctly compares the wavelengths of waves with different amounts of energy?

A As the wavelength gets shorter, energy in the wave decreases.

B Wavelength has no relationship with energy.

C As the wavelength of a wave gets shorter, energy increases.

D As the wavelength gets longer, amplitude decreases with energy.

6

Describe the effect of increasing frequency on electromagnetic spectrum waves.

80 | Characteristics and Use of the Electromagnetic Spectrum

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Earth’s Tilt and Seasons

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81

STEMscopedia People have been marking the changes of seasons for thousands of years. As weather patterns change, we notice that the air feels different. The Sun appears to be higher or lower in the sky. The amount of daylight seems shorter or longer than it was just a few weeks before.

Plants show seasonal changes as well. Look at the tree below, photographed in each season for a year.

Have you ever thought about what triggers changes in leaves like this? What is it that causes them to VSURXW OHDYHV LQ WKH VSULQJ RU FKDQJH FRORUV LQ WKH IDOO" %HOLHYH LW RU QRW WKHVH FKDQJHV DUH LQÀ XHQFHG E\ Earth’s revolution around the Sun. Seasons are the four natural divisions of the year based on changes in temperature. These are due to varying amounts of sunlight.

does 1. How volution s re Earth’ the Sun around VHDVRQDO FH LQş XHQ s in plants e chang animals? and

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Earth’s Tilt and Seasons | 83

STEMscopedia First, we need to understand how Earth moves. Earth has two movements, rotation and revolution.

A rotation is when an object turns around a center point called an axis. An axis is the imaginary line through Earth that extends from the North Pole to the South Pole and is the center of Earth’s rotation.

(DUWK VSLQV RQ LWV D[LV OLNH D FKLOG¶V WRS RU D ¿ JXUH VNDWHU SHUIRUPLQJ D VSLQ 7KLV PRYHPHQW WDNHV DERXW 24 hours to complete and causes Earth’s day and night.

Earth also revolves around the Sun. A revolution is the movement of one object around a center or another object. In this case, Earth and other planets revolve around the Sun, which is at the center of our solar system. This movement of Earth takes just over 365 days, the length of a year.

Both of these movements happen at the same time.

Rotation of Earth

Earth’s revolution around the Sun

It is easy to confuse these movements. A rotation is a spin or a turn. All eight planets rotate, so this is not unique to Earth. During the formation of the solar system, bits of dust and gas gathered to form the planets, and while they did so, the entire solar system was rotating in the same general direction.

As more debris collected, the forces exerted on early Earth and other objects began the rotation. This is thought to be the reason that all celestial objects, including planets and the Sun, rotate even today.

Earth and the other planets in the solar system revolve around the Sun. This revolution is caused by a combination of forward movement and the pull of the Sun’s gravity, causing Earth and other planets to follow a curved path.

84 | Earth’s Tilt and Seasons

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STEMscopedia

t pare m o f C .

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Earth’s Tilt and Seasons | 85

STEMscopedia We know that the weather is warmer in the summer than it is in the winter. It is easy to think that this is because Earth is closer to the Sun in summer and farther away in winter. That is not true, though.

Earth is roughly the same distance from the Sun throughout its orbit. An orbit is a curved path followed by a satellite as it revolves around an object. It is the path that Earth takes as it completes a revolution around the Sun. Earth is heated by the Sun as it completes its revolution. However, some of the Sun’s rays hit Earth more directly than others. As you can see in the second image below, the Sun’s radiation hits the tropics of Earth, near the equator, at a 90-degree angle. This results in a strong concentration of rays in a smaller overall area of the planet. Since areas near the equator experience more direct heating at this part of Earth, it leads to warmer temperatures there. Areas that receive more indirect heating are cooler, like the poles. Indirect solar rays are angled or spread out. Temperatures are lower where the Sun’s rays are indirect.

Solar Radiation and Earth Less concentrated radiation over a larger surface area

30° 45° 60°

Sun’s rays More concentrated radiation over a smaller surface area

90°

Here is a closer look at the difference in how the Sun’s rays hit Earth’s surface at different latitudes.

Low latitudes are places near Earth’s equator, such as Sri Lanka and Central America. Middle latitudes are locations such as the United States and Canada, China, and Argentina in South America. The Arctic Circle and Antarctica are in the polar latitudes.

45°

90° Earth’s surface, low latitudes

86 | Earth’s Tilt and Seasons

30° Earth’s surface, middle latitudes

Earth’s surface, polar latitudes

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STEMscopedia

The Sun’s uneven heating of Earth is not the whole reason that our planet has seasons, though. In the diagram on the previous page, the two areas that receive the Sun’s radiation at a 30-degree angle are close to the North Pole and the South Pole.

Notice that we did not say that the North and South Poles receive the same amount of radiation at the same time. Earth’s axis is tilted at 23.5 degrees from the north. This means that the axis of Earth is slightly slanted and is not straight up and down. This slant is known as a tilt.

would 3. How s on n conditio be Earth t if n differe is were s ax Earth’ tilted? not

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Earth’s Tilt and Seasons | 87

STEMscopedia So why don’t the North and South Poles experience the same temperatures at the same time? As tilted Earth revolves around the Sun, different parts of the planet get differing amounts of radiation from the Sun throughout the year.

7KH SODQHW FDQ EH GLYLGHG LQWR KHPLVSKHUHV 7KH SUH¿ [ hemi- means “half,” so hemisphere means “half of a sphere.”

Because Earth is tilted, the Sun heats the northern and southern hemispheres unevenly. One is always receiving more direct radiation from the Sun. In June, when Earth is at the point in its orbit where the northern hemisphere is receiving the most direct radiation from the Sun, it is summer there. At the same time, the southern hemisphere is experiencing winter. The North Pole has 21 hours of daylight in a 24-hour period, while the South Pole only has about 3 hours of daylight.

Six months later, in December, Earth is farther along its orbit around the Sun, and the southern hemisphere receives the most direct radiation from the Sun. It is winter in the northern hemisphere and summer in the southern. The North Pole only experiences about 3 hours of daylight in a 24-hour period, while the South Pole has about 21 hours of daylight.

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88 | Earth’s Tilt and Seasons

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STEMscopedia What is Earth’s position when the northern hemisphere is experiencing summer? We know that during summer, the northern hemisphere is pointed toward the Sun. The North Pole is bathed in sunlight for most of the time it takes for Earth to complete a rotation. The southern hemisphere is in darkness for more than half of the rotation, and the southern hemisphere is colder because it is receiving more indirect light from the Sun. We would model this arrangement like this.

23.5° Northern hemisphere

Equ ato r

Sun’s rays Southern hemisphere

The image shows Earth and the Sun when it is summer in the northern hemisphere and winter in the southern hemisphere. Summer in the northern hemisphere begins around June 21st, when the northern hemisphere experiences the longest daylight period of the year. This is known as the summer solstice.

Three months after the summer solstice, both hemispheres experience a day around September 21st where the amount of sunlight and darkness are equal—an event known as the autumnal equinox. This starts the fall season.

Three months after this, Earth experiences the shortest day of the year in the northern hemisphere and the longest in the southern hemisphere. This event falls around December 21st and is known as the winter solstice in the northern hemisphere. Earth and the Sun are arranged like the image below.

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Earth’s Tilt and Seasons | 89

STEMscopedia 23.5° Northern hemisphere

Equ ato r

Sun’s rays Southern hemisphere

Finally, three months later, Earth progresses in its orbit around the Sun and experiences another day around March 21st where the amount of sunlight and darkness is the same in both hemispheres. We call this the vernal equinox, and it marks the start of the spring season in the northern hemisphere.

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90 | Earth’s Tilt and Seasons

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STEMscopedia Kelly Rohan University of Vermont Kelly Rohan is a professor and director of the Clinical Training Program at the University of Vermont. As a psychologist, she and her team research Seasonal Affective Disorder, which is a mood disorder thought WR EH LQÀ XHQFHG E\ VHDVRQDO FKDQJHV 5RKDQ LV FXUUHQWO\ OHDGLQJ D ORQJ WHUP VWXG\ LQYHVWLJDWLQJ WKH HIIHFWV RI OLJKW WKHUDS\ DQG WDON WKHUDS\ RQ SDWLHQWV ZKR KDYH HPRWLRQDO GLI¿ FXOWLHV LQ WKH ZLQWHU PRQWKV It is thought that as many as 6 out of 100 people suffer from Seasonal Affective Disorder. Rohan KDV VDLG VKH EHOLHYHV WKH RQVHW RI IDOO DQG WKH FRROHU ZHDWKHU HDFK 2FWREHU LQÀ XHQFHV VXIIHUHUV RI the disorder. She has noted that the disorder seems to be more common at higher latitudes where temperatures are colder and winters bring even less sunlight than at lower latitudes. She also notes this is an important area of research because as many as 20% of people who suffer from mood disorders are affected by changes in seasons.

Psychologist Kelly Rohan researches the effects of the seasons on mood and investigates potential treatments, such as light and talk therapy.

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Earth’s Tilt and Seasons | 91

STEMscopedia Earth is tilted 23.5 degrees on its axis. This tilt causes the Sun to heat different parts of Earth unevenly.

As Earth revolves around the Sun, uneven heating due to Earth’s tilt causes the changes in sunlight and temperature that we know as seasons.

Connect It How do the tilt of Earth and its revolution cause seasons?

Earth’s revolution around the Sun causes seasonal changes because Earth is tilted on its axis as it completes its revolution. This causes uneven heating on various parts of Earth throughout the year. This causes changes in the amount of daylight and temperatures that organisms respond to by dropping or sprouting leaves, migrating, and reproducing.

92 | Earth’s Tilt and Seasons

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STEMscopedia 1

Which of the following accurately describes why Earth has seasons?

A Earth is closer to the Sun during the summer and farther away in winter.

B Earth revolves on a tilted axis around the Sun. C Earth changes the direction of its rotation as it progresses through each season.

D The Sun revolves on a tilted axis around Earth.

2

Earth’s seasons are affected by all of the following except– A the observer’s hemisphere and location on Earth.

B the angle of Earth’s axial tilt.

C the speed of Earth’s revolution around the Sun. D migratory and other patterns of plants and animals.

3

Which of the following statements correctly describes the differences between solstices and equinoxes?

A Solstices and equinoxes mark the days when Earth’s rotation slows down or speeds up.

B Solstices are the longest and shortest days of the year; equinoxes happen when the amounts of sunlight and darkness are equal.

C Solstices only happen in the spring and fall; equinoxes happen in the summer and winter.

D Equinoxes are the longest and shortest days of the year; solstices happen when the amounts of sunlight and darkness are equal.

4

Which two seasons is the southern hemisphere experiencing in the diagram below?

A B C D

Spring and summer Summer and autumn Autumn and winter Winter and spring

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Earth’s Tilt and Seasons | 93

STEMscopedia 5

A student used a light bulb and four playground balls to model the seasons. Label the diagram below with the correct seasons based on the location of the ball and amount of sunlight available to both hemispheres.

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94 | Earth’s Tilt and Seasons

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Ocean Tides

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95

STEMscopedia Ocean water is always moving and changing. In the scene below, water covered the sand and soil in this area just a few short hours ago. About six hours from now, the water level will once again be higher. You can see this pattern at coastlines around the world. Every six hours, the water becomes lower, and then six hours after that, it becomes higher. Have you ever thought about why this happens?

t 1. Wha s? tide causes

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Ocean Tides | 97

STEMscopedia It might seem strange to talk about the Moon in a discussion of tides, which occur on Earth. But the Moon plays a huge part in the formation and cycles of tides on Earth. The Moon exerts a gravitational pull on Earth. A gravitational pull is the attraction between two objects due to the invisible force of gravity. The gravitational pull from the Moon is mostly responsible for the tides we experience on Earth.

What is a tide? A tide is the rise and fall of sea levels caused by the gravitational attraction of the Moon and the Sun. Earth interacts with both celestial bodies because the Moon revolves around Earth as Earth revolves around the Sun. Both the Moon and the Sun exert a gravitational attraction on Earth. This attractive force causes slight bulges of water on the sides of Earth that face either the Sun or the Moon.

Since the Moon has the largest force exerted on Earth’s water, we show this in the image below. Note how the side of Earth facing the Moon has water built up on that side as the Moon pulls the water on Earth toward it. The opposing side of Earth also experiences a water buildup, but this is caused by the rotation of the planet.

The Sun has tremendous mass and has a gravitational pull on Earth. However, since the Moon is much closer to Earth than the Sun is, the Moon actually exerts a larger force on Earth, even though it is smaller than the Sun. The Sun, along with Earth’s rotation, causes these water bulges on Earth, too, but they are smaller because the Sun is so far from Earth.

98 | Ocean Tides

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STEMscopedia cities rotate through these areas of more and less water buildup throughout the day and night. This is what causes the tides in those cities to change.

2. Wh y places do most exper on Earth ie higgh t nce two ide two low s and t per d ides ay?

Daily Tides Most coastal areas on Earth experience two high tides and two low tides per day. A high tide occurs when the tide is at its greatest elevation. A low tide happens when the tide is at its lowest elevation of the day. Looking at the images below, we can see how a city rotates through two high tide and two low tide areas per day.

Cairo, Egypt

Cairo, Egypt

Galveston, TX, USA

Galveston, TX, USA

Overhead View of Earth from Space

Six Hours Later

The images above show how two cities can experience high or low tides based on where the FLW\ LV UHODWLYH WR WKH WLGDO EXOJHV ,Q WKH ¿ UVW LPDJH *DOYHVWRQ 7; LV URWDWLQJ WKURXJK DQ area of less water, causing a lower tide in that area than in Cairo, Egypt, which is rotating through an area of large water buildup and thus is experiencing a high tide. In the second LPDJH VL[ KRXUV KDYH SDVVHG *DOYHVWRQ¶V WLGDO OHYHOV DUH LQFUHDVLQJ DV (DUWK URWDWHV through an area of more water, and Cairo’s tidal levels are decreasing. © Accelerate Learning Inc. – All Rights Reserved

Ocean Tides | 99

STEMscopedia

3. If y ou beach were at th e du higgh t ring both a ide tide, ho and a low w beach would the look both tim during es?

100 | Ocean Tides

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STEMscopedia A spring tide, or king tide, is not a reference to a season but rather is based on an observation that tides seem to spring forth twice a month.

Spring tides are those with the largest daily tidal range, which occurs when the Sun, Earth, and the Moon line up with each other and the gravitational forces are combined, causing higher high tides and lower low tides. This creates an exaggerated tidal bulge because both the Sun and the Moon are pulling on Earth’s waters in the same direction.

When the Sun, Earth, and the Moon are in a straight line, this alignment causes Earth to have an unusually high and low tide. This is called a spring tide and happens twice in a lunar month.

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Ocean Tides | 101

STEMscopedia full moon happens when Earth is between the Sun and the Moon and all of the illuminated portion is seen from Earth. Two weeks later, when the Moon is directly between the Sun and Earth and none of the illuminated portion is seen from Earth, there is a new moon and another spring tide.

In the image above, we can see how the Sun’s gravitational pull combines with the Moon’s to create a larger overall tidal bulge twice a month, when the Sun, Earth, and the Moon are in a straight line. The Sun’s gravitational pull combines with the Moon’s to make high tides even higher than normal and low tides lower than normal.

4. How sprinng do the a tides d nd neap the w iffer in ater they c levels on coa reate stlines ?

102 | Ocean Tides

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STEMscopedia The positions of the Sun and the Moon also cause another type of tide called a neap tide. A neap tide occurs when the Sun, Earth, and the Moon form a 90-degree angle. It causes the smallest daily range of tides during the month, meaning that the difference between a high and low tide is not as big as it is during a normal tide.

The image shows the alignment of the Sun, Earth, and the Moon during a neap tide. Twice a month, these three form a right angle, and the lunar tide is arranged in the opposite direction from the solar tide. As a result, coasts on Earth experience a smaller difference between high tide and low tide levels.

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Ocean Tides | 103

STEMscopedia and the lunar cycle is in the waxing phase, the Moon is in its ¿ UVW TXDUWHU phase. About two weeks later, when the left half of the Moon is illuminated and the lunar cycle is in the waning phase, we say the Moon is in its ODVW TXDUWHU or WKLUG TXDUWHU r . In both positions, the lunar tide caused by the gravitational pull of the Moon is in a different direction from the Sun’s gravitational force, causing a perpendicular overlap of tidal bulges. This overlap results in a lower-than-normal high tide and a higher-than-normal low tide.

5. Exp the p lain how the M ositions of oo 6XQ LQ n and the and th WKH Ş UVW phase ird quarter o cause f the Moon a nea p tide .

104 | Ocean Tides

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STEMscopedia Andrew Short University of Sydney Andrew Short is a professor at the University of Sydney in Australia, located in New South Wales. He studies the natural processes and human impacts at the shoreline and coastal zones of Australia. He studies the beach and barrier systems of Australia, including waves and tidal environments.

Since 1991, he has been the national coordinator of the Australian Beach Safety and Management Program in cooperation with Surf Life Saving Australia, an organization that provides advice for beach YLVLWRUV RQ À DJV KD]DUGV DQG PDULQH OLIH DW WKH EHDFK ZRUNLQJ WR PDNH EHDFK YLVLWV VDIHU DQG PRUH enjoyable. He has also written books on beaches and barrier systems.

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Ocean Tides | 105

STEMscopedia A tide is the rise and fall of sea levels caused by the gravitational attraction of the Moon and the Sun. The gravitational pull from the Moon is mostly responsible for the tides we experience on Earth. Most coastal areas on Earth experience two high tides and two low tides per day. A high tide occurs when the tide is at its greatest elevation. A low tide happens when the tide is at its lowest elevation of the day.

Spring tides are those with the largest daily tidal range, which occurs when the Sun, Earth, and the Moon line up with each other and the gravitational forces are combined, causing higher high tides and lower low tides. A neap tide occurs when the Sun, Earth, and the Moon form a 90-degree angle. It causes the smallest daily range of tides during the month, meaning that the difference between a high DQG ORZ WLGH LV QRW DV ELJ DV LW LV GXULQJ D QRUPDO WLGH 7KLV KDSSHQV ZKHQ WKH 0RRQ LV LQ LWV ¿ UVW DQG third quarter positions.

Connect It +RZ GR WKH 6XQ¶V DQG WKH 0RRQ¶V SRVLWLRQV LQÀ XHQFH WLGHV RQ (DUWK" The Sun and the Moon both pull on Earth’s oceans, causing bulges of ocean water on the side of Earth facing them. Earth rotates through these areas of higher and lower volumes of ocean water, causing high and low tides every six hours. Spring tides happen when the Sun, Earth, and the Moon are directly aligned, resulting in exaggerated high and low tides. Neap tides form twice a month when the Moon forms a right angle with Earth and the Sun, which causes higher low tides and lower high tides.

These boats were in the water during high tide and are now resting on the sand because it is low tide.

106 | Ocean Tides

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STEMscopedia 1

The highest high tides and the lowest low tides are called spring tides. Spring tides occur when– A Earth rotates through bulges of water every six hours.

B the Sun, Earth, and the Moon form a right angle.

C WKH 0RRQ LV LQ LWV ¿ UVW DQG WKLUG TXDUWHU SKDVHV D the Sun, Earth, and the Moon are in a straight line.

2

:KDW WZR IDFWRUV LQÀ XHQFH WKH LPSDFW RI WKH 6XQ DQG WKH 0RRQ RQ WLGHV" A The distance from Earth and the size of the Sun and the Moon B The time of day and the season C The direction of Earth’s rotation and the position of the Moon D 7KH DPRXQW RI JUDYLW\ GXULQJ D VSHFL¿ F WLPH LQ WKH OXQDU SKDVH

3

What positions are the Sun, Earth, and the Moon in during a period of neap tides?

A The Sun and the Moon are slightly farther away from Earth than normal.

B The Sun and the Moon form a right angle with Earth in the middle.

C The Sun, Earth, and the Moon are in a straight line.

D The Moon is at the full or new phase in the lunar cycle.

4

Earth experiences a ________ or _______ tide every ____ hours.

5

How long does it take from the time Earth experiences a spring tide until Earth experiences the next neap tide? _____________

6

Describe how an observer on Earth could tell when their coastline is experiencing a spring tide.

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Ocean Tides | 107

Solids, Liquids, and Gases

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109

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Solids, Liquids, and Gases | 111

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112 | Solids, Liquids, and Gases

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Solids, Liquids, and Gases | 113

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114 | Solids, Liquids, and Gases

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Solids, Liquids, and Gases | 115

STEMscopedia N-

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116 | Solids, Liquids, and Gases

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STEMscopedia 7R KHOS XV XQGHUVWDQG ZK\ OLTXLGV EHKDYH GLIIHUHQWO\ WKDQ VROLGV OHW¶V ORRN DW KRZ KHDW FKDQJHV WKH PRYHPHQW RI PROHFXOHV Liquid is a state RI PDWWHU ZLWK D GH¿ QLWH YROXPH EXW QR GH¿ QLWH VKDSH /LTXLGV KDYH PRUH KHDW HQHUJ\ WKDQ VROLGV ,I KHDW HQHUJ\ LV DGGHG WR WKH PROHFXOHV RI D VROLG WKH\ JDLQ HQHUJ\ DQG DUH DEOH WR PRYH DURXQG ,I HQRXJK KHDW LV DGGHG WKH\ FDQ EUHDN WKH WLJKW ERQGV EHWZHHQ PROHFXOHV DQG EHJLQ WR VSUHDG RXW 2QFH WKH\ VSUHDG RXW WKH\ FDQ PRYH DQG À RZ past one another. /HW¶V ORRN DW WKH VKDSH RI OLTXLGV 7KLV DELOLW\ WR À RZ PHDQV WKDW WKH PROHFXOHV LQ D OLTXLG KDYH D PRUH ORRVH IRUP DQG VWUXFWXUH WKDQ PROHFXOHV LQ D VROLG 7KH\ DUH VWLOO FORVH WRJHWKHU EXW KDYH HQRXJK VSDFH DQG HQHUJ\ WR PRYH DQG À RZ /LTXLGV GR KDYH D PHDVXUDEOH GH¿ QLWH YROXPH :KHQ WKHUPDO HQHUJ\ LV DGGHG WR D VROLG VXFK DV LFH WKH WKHUPDO HQHUJ\ H[FLWHV WKH PROHFXOHV LQ WKH VROLG PDNLQJ WKHP PRYH IDVWHU 7KLV FKDQJHV WKHLU VWUXFWXUH ,W FDXVHV WKHP WR VSUHDG RXW DQG EHJLQ WR À RZ SDVW RQH DQRWKHU 7KLV LV NQRZQ DV PHOWLQJ ,I WKH WKHUPDO HQHUJ\ LQ D OLTXLG LV WDNHQ DZD\ WKH RSSRVLWH KDSSHQV DQG WKH OLTXLG WXUQV LQWR D VROLG 7KLV SURFHVV LV FDOOHG VROLGLI\LQJ

Thermal energy added (melting)

Thermal energy removed (solidifying)

Solid

Liquid

Molecules are in a fixed pattern but vibrate.

Molecules are packed closely but can flow.

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Solids, Liquids, and Gases | 117

STEMscopedia shape of the container they are in.

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118 | Solids, Liquids, and Gases

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STEMscopedia *DVHRXV PDWWHU GRHV QRW VHHP OLNH LW ZRXOG KDYH PDVV RU WDNH XS VSDFH EXW LW does! Gas LV D VWDWH RI PDWWHU ZLWK DQ LQGH¿ QLWH YROXPH DQG VKDSH 6R DOWKRXJK PDQ\ DUH KDUG WR VHH JDVHV WDNH XS VSDFH DQG FDQ FKDQJH KRZ PXFK VSDFH WKH\ RFFXS\ 7KLV LV GXH WR WKH VWUXFWXUH RI WKH PROHFXOHV LQ WKH PDWWHU +RZ LV PDWWHU LQ D JDVHRXV IRUP VWUXFWXUHG" 7KH PROHFXOHV DUH IDU DSDUW DQG KDYH HQRXJK HQHUJ\ WR RYHUFRPH WKH ERQGV ZLWK RWKHU PROHFXOHV 7KH\ DUH DEOH WR ERXQFH DURXQG PRYLQJ LQ YDULRXV GLUHFWLRQV LQGHSHQGHQWO\ RI RQH DQRWKHU *DV PROHFXOHV H[SDQG WR ¿ W WKH VSDFH DYDLODEOH WR WKHP ZKLFK FDXVHV WKHLU VKDSH DQG YROXPH WR EH LQGH¿ QLWH +HUH LV D VLGH E\ VLGH FRPSDULVRQ RI PDWWHU LQ DOO WKUHH VWDWHV 1RWLFH KRZ WKH SDUWLFOHV LQ D JDV DUH YHU\ VSUHDG RXW FRPSDUHG WR WKH RWKHU WZR VWDWHV

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STEMscopedia Boiling Thermal energy added (evaporating)

Thermal energy removed (condensing)

Liquid

Gas

Molecules are packed closely but can flow.

Molecules are separated and move quickly and randomly.

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120 | Solids, Liquids, and Gases

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STEMscopedia WKLV LI \RX KDYH HYHU ¿ OOHG D ELF\FOH WLUH ZLWK DLU 7KH SXPS LQFUHDVHV WKH DPRXQW RI DLU PROHFXOHV LQ WKH WLUH ZLWKRXW LQFUHDVLQJ WKH WLUH¶V YROXPH WKXV SODFLQJ PRUH PROHFXOHV LQVLGH WKH VDPH DPRXQW RI VSDFH LQFUHDVLQJ WKH SUHVVXUH LQ WKH WLUH

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Solids, Liquids, and Gases | 121

STEMscopedia Marivi Fernández-Serra Stony Brook University 0DULYL )HUQiQGH] 6HUUD DQG KHU UHVHDUFK WHDP PDGH D PDMRU GLVFRYHU\ LQ DERXW WKH VWUXFWXUH RI ZDWHU PROHFXOHV 6FLHQWLVWV KDYH ORQJ GHEDWHG ZKHWKHU ZDWHU PROHFXOHV DUH PRUH OLNH D OLTXLG RU VROLG 7KH\ IRXQG WKDW WKH YLEUDWLRQV EHWZHHQ ZDWHU PROHFXOHV PRYH LQ D XQLTXH PDQQHU VLQFH WKH ERQGV between atoms are constantly broken and reformed.

'U )HUQiQGH] 6HUUD KDV DOVR GRQH UHVHDUFK RQ VHPLFRQGXFWLQJ PDWHULDOV DQG LV ZRUNLQJ RQ GHYHORSLQJ D sensor for dark matter.

122 | Solids, Liquids, and Gases

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STEMscopedia 6ROLGV OLTXLGV DQG JDVHV YDU\ LQ WKHLU VWUXFWXUH VKDSH YROXPH DQG PROHFXODU HQHUJ\ 6ROLGV KDYH WKH OHDVW PROHFXODU HQHUJ\ D GH¿ QLWH VWUXFWXUH VKDSH DQG YROXPH /LTXLGV KDYH PRUH HQHUJ\ WKDQ VROLGV D GH¿ QLWH YROXPH DQG DQ LQGH¿ QLWH VKDSH *DVHV KDYH ERWK DQ LQGH¿ QLWH YROXPH DQG VKDSH EHFDXVH WKH\ KDYH VR PXFK PROHFXODU HQHUJ\ WKDW WKH VWUXFWXUH RI WKH SDUWLFOHV DOORZV PRUH VSDFH EHWZHHQ WKHP

Connect It How does thermal energy change the behavior of molecules in a hot air balloon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

7KLV LPDJH VKRZV WKH VWUXFWXUH DQG YROXPH RI PROHFXOHV LQVLGH DQG RXWVLGH RI D KRW DLU EDOORRQ :KHUH WKH DLU LQVLGH WKH EDOORRQ LV KHDWHG WKH PROHFXOHV DUH IDUWKHU DSDUW DQG OHVV GHQVH 2XWVLGH RI WKH EDOORRQ WKH DWPRVSKHULF DLU LV FRROHU FDXVLQJ WKH PROHFXOHV WR be closer together and more dense.

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Solids, Liquids, and Gases | 123

STEMscopedia 7HPSHUDWXUH LV UHODWHG WR WKH NLQHWLF HQHUJ\ RI DWRPV 7KH IDVWHU WKH DWRPV PRYH WKH KLJKHU WKH WHPSHUDWXUH RI WKH VXEVWDQFH $V WKH NLQHWLF HQHUJ\ RI DWRPV GHFUHDVHV WKH DWRPV PRYH PRUH VORZO\ DQG WKH WHPSHUDWXUH GHFUHDVHV 7KHVH FKDQJHV LQ WHPSHUDWXUH FDQ DOVR PHDQ FKDQJHV LQ D VXEVWDQFH¶V VWDWH RI PDWWHU 6WDWHV RI PDWWHU LQFOXGH VROLG OLTXLG JDV DQG SODVPD DV VKRZQ LQ WKH IROORZLQJ LPDJH

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124 | Solids, Liquids, and Gases

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STEMscopedia 1

:KLFK RI WKH IROORZLQJ VWDWHPHQWV DFFXUDWHO\ FRPSDUHV PROHFXODU HQHUJ\ LQ OLTXLGV JDVHV DQG VROLGV" A /LTXLGV KDYH WKH VDPH DPRXQW RI PROHFXODU HQHUJ\ DV VROLGV EXW ERWK KDYH PRUH WKDQ JDVHV B /LTXLGV KDYH WKH VDPH DPRXQW RI PROHFXODU HQHUJ\ DV VROLGV EXW ERWK KDYH OHVV WKDQ JDVHV C /LTXLGV KDYH OHVV PROHFXODU HQHUJ\ WKDQ VROLGV EXW PRUH WKDQ JDVHV D /LTXLGV KDYH PRUH PROHFXODU HQHUJ\ WKDQ VROLGV EXW OHVV WKDQ JDVHV

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Physical and Chemical Changes

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127

STEMscopedia ,PDJLQH \RX DUH EDNLQJ D FDNH <RX FRPELQH WKH LQJUHGLHQWV²PLON HJJV À RXU DQG PRUH :KHQ \RX combine them into a batter, they are a substance that is stretchy, moldable, and pours when you WUDQVIHU LW WR D SDQ $V WKH FDNH EHJLQV WR EDNH LQ WKH RYHQ LW DGRSWV D GU\ FRQVLVWHQF\ EHFRPHV À XII\ and rises. Has a new substance been created?

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Physical and Chemical Changes | 129

STEMscopedia All things are made of matter. Matter is anything that has volume and mass. The physical properties of matter include the attributes that we can observe or measure without making the matter different.

A physical property is a characteristic that can be observed or measured without changing the VXEVWDQFH 7KLV LQFOXGHV PDVV YROXPH WH[WXUH WHPSHUDWXUH VKDSH DQG À H[LELOLW\

This brick wall has a rough texture. Texture is a physical property that can be observed without changing the brick.

0DWWHU DOVR KDV FKHPLFDO SURSHUWLHV VXFK DV À DPPDELOLW\ DFLGLW\ RU UHDFWLYLW\ Chemical properties can only be observed or measured when atoms, the basic building blocks of all matter, rearrange during a chemical change.

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130 | Physical and Chemical Changes

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STEMscopedia ripping or tearing paper or burning a liquid such as gasoline. There are two main types of changes that matter can undergo. These are called physical and chemical changes.

In a physical change, matter is changed without forming a new substance. This includes changing in size or in state of matter. Some examples of physical changes include cutting wood, sanding a surface to make it smooth, and melting or freezing ice. A new substance is not created, although the matter may look or feel different.

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Physical and Chemical Changes | 131

STEMscopedia chemical change, a new substance is created through a chemical reaction. Examples include the rusting of a nail, burning the wick on a candle, or dissolving a substance in acid. The chemical properties of the substance may or may not change when a new substance is created.

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132 | Physical and Chemical Changes

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STEMscopedia Let’s take a closer look at what happens when matter undergoes a physical change. The atoms making up the substance may move together or farther apart, but they do not rearrange and form new bonds with other atoms. :KHQ ZDWHU FKDQJHV LWV SK\VLFDO VWDWH IURP VROLG LFH WR OLTXLG ZDWHU RU IURP OLTXLG WR JDVHRXV ZDWHU vapor, the molecules move farther apart. They still consist of hydrogen and oxygen atoms bonded to each other. Changes in matter’s state are always physical. Temperature changes are examples of SK\VLFDO FKDQJHV :KHQ PDWWHU KHDWV XS RU FRROV GRZQ WKH DWRPV PD\ PRYH FORVHU WRJHWKHU RU IDUWKHU apart, but a new substance is not created.

Matter can increase or decrease in size without affecting the arrangement of particles. Stretching a rubber band and chopping wood are examples of size changes that are also physical changes.

Stretching a rubber band is an example of a physical change. The matter may change in size, but it does not change in composition. :KHQ ZH À DWWHQ RXW GRXJK WR PDNH EDNHG JRRGV ZH DUH FKDQJLQJ WKH PDWWHU¶V VKDSH LQ D SK\VLFDO ZD\ Rolling mud into a ball is another example of changing shape. These are physical changes.

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Physical and Chemical Changes | 133

STEMscopedia physical change. For example, covering a wall with a coat of paint will cause a color change, but it is a physical change since atoms are not rearranged and the matter does not form a new substance.

Painting a wall is an example of a physical change since the wall is not changing composition.

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134 | Physical and Chemical Changes

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STEMscopedia In a chemical change, atoms are rearranged, and a new substance is formed. New molecules or compounds may be formed, and this makes the substance change its overall composition.

7KHUH DUH UHFRJQL]DEOH VLJQV RI D FKHPLFDO FKDQJH 7KH ¿ UVW LV JDV SURGXFWLRQ *DV UHVXOWLQJ IURP D chemical change usually is seen as bubbles. A precipitate may form when a new substance is created.

This can be seen in cases where two liquids are mixed and a solid forms at the bottom of the container.

Sometimes the solid is the same color as one or both of the liquids; other times it is not.

Sometimes, the new substance is a solid that collects at the bottom of the container.

This is known as a precipitate.

One example of precipitate formation is when silver nitrate and sodium chloride are mixed together in water. A new substance called silver chloride forms as a solid and collects.

Color changes can indicate a chemical change as long as they are sudden, drastic, and irreversible.

Examples of this type of change include pH indicator paper (litmus paper) changing colors, or red cabbage juice changing color when reacting with another substance.

Drastic temperature changes can indicate chemical changes. Reactions that release or absorb heat are good examples of this kind of change. Hot and cold packs are examples of products featuring this kind of reaction. If the mixing of two substances creates a new substance and causes atoms to rearrange, a chemical change has taken place.

As the temperature increases, the reactants in a chemical change have more kinetic energy, speeding up the molecules. As the molecules increase in speed, there is an increase in collisions, causing the reaction to occur faster. This results in a faster formation of products.

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Physical and Chemical Changes | 135

STEMscopedia The law of conservation of mass states that mass is neither created nor destroyed in chemical reactions.

In a chemical change, atoms are rearranged, and a new substance is formed. The mass of any one HOHPHQW DW WKH VWDUW RI WKH UHDFWLRQ ZLOO HTXDO WKH PDVV RI WKDW HOHPHQW ZKHQ WKH UHDFWLRQ ¿ QLVKHV 1R PDVV LV ORVW )RU H[DPSOH DV ZRRG EXUQV LQ D ¿ UH LW FRPELQHV ZLWK R[\JHQ DQG FKDQJHV WR DVK FDUERQ GLR[LGH DQG ZDWHU YDSRU 7KH JDVHV À RDW DZD\ OHDYLQJ WKH DVK EHKLQG ,I \RX PHDVXUHG WKH PDVV RI WKH ZRRG EHIRUH \RX ZRXOG ¿ QG WKDW WKH FRPELQHG PDVV RI WKH DVK WKH R[\JHQ XVHG LQ WKH ¿ UH DQG WKH gases produced was the same as the starting mass.

136 | Physical and Chemical Changes

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STEMscopedia Dr. Harry Coover Eastman Chemical Company Dr. Harry Coover was an inventor best known for creating the adhesive best known as superglue. Coover was originally assigned to work in Eastman Chemical Company’s labs with plastic compounds to develop FOHDU JXQVLJKWV IRU VROGLHUV ¿ JKWLQJ LQ :RUOG :DU ,, +H GLVFRYHUHG WKH FRPSRXQG IRU VXSHUJOXH E\ accident during this time. &RRYHU DSSOLHG IRU D SDWHQW EXW ZDV UHMHFWHG ,W WRRN KLP PRUH WKDQ ¿ IWHHQ \HDUV WR EULQJ WKH SURGXFW WR the public, where it became useful in a wide variety of places, including homes and hospital emergency rooms. In all, Coover won 460 patents for his inventions, although superglue was by far the most famous one. For his lifetime achievements, Coover was awarded the National Medal of Technology and Innovation just before his death in 2011.

Inventor Harry Coover is credited with the invention of cyanoacrylates, a group of chemical compounds forming superglue.

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Physical and Chemical Changes | 137

STEMscopedia 0DWWHU FDQ FKDQJH LQ WZR PDLQ ZD\V 7KH ¿ UVW LV E\ D SK\VLFDO FKDQJH ZKHUH QR QHZ VXEVWDQFH LV created, although the atoms in the matter can get closer or farther apart. Examples of physical changes include tearing paper, cutting fabric with scissors, or melting crayons. Chemical changes happen when a new substance is formed. This happens when the atoms of a substance rearrange and form new FRPSRXQGV ([DPSOHV RI FKHPLFDO FKDQJHV LQFOXGH EDNLQJ EURZQLHV RU EXUQLQJ ¿ UHZRRG

Connect It Does baking result in the creation of a new substance?

In most cases, yes. Baking causes an addition of heat to a mixture of substances, and during this process, the atoms of the mixture rearrange and create a new substance. This process is an example of a chemical reaction.

138 | Physical and Chemical Changes

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STEMscopedia 1

:KLFK RI WKH IROORZLQJ H[DPSOHV LV 127 D SK\VLFDO FKDQJH" A A person repainting a bicycle B Rain falling on a bicycle left outside C Rust forming on a bicycle chain D Cutting an old bicycle with a saw for scrap metal

2

7KH VWRPDFK LQ WKH KXPDQ ERG\ FRQWDLQV DFLG WKDW EUHDNV GRZQ IRRG LQWR XVDEOH SDUWLFOHV :KLFK RI the following best describes the process of digestion in the body?

A An example of a physical change B An example of a chemical property C An example of a physical property D An example of a chemical change

3

:KLFK RI WKH IROORZLQJ VWDWHPHQWV LV WUXH DERXW WKH SK\VLFDO SURSHUWLHV RI REMHFWV" A They can be observed without changing the substance chemically.

B They cannot be observed without changing the substance chemically.

C 7KH\ LQFOXGH H[DPSOHV VXFK DV DFLGLW\ DQG À DPPDELOLW\ D They can be changed by burning, magnetizing, or cutting.

4

Fill in the blanks with the word physicall to describe a physical change, or chemicall to describe a chemical change. ___________ No new substance forming when matter undergoes a change ___________ Combining multiple chemicals to change the water chemistry in a pool ___________ Bending a glow stick to make it glow ___________ Ironing a shirt before wearing it ___________ An artist burning a piece of wood to make an intricate design

5

Describe at least three ways to physically change a piece of fabric such as an old towel.

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Physical and Chemical Changes | 139

Elements and Compounds

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141

STEMscopedia One very common compound you probably have experience with daily is salt. Made from sodium and chlorine, it is commonly found in your food, excreted as sweat, and evaporated from oceans all over the world. But what do you really know about salt? Can you spot it on the Periodic Table of Elements?

lt ble sa a t n a he 1. C d on t n u o f be Table ic d io r Pe ents? m le E of

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Elements and Compounds | 143

STEMscopedia Let’s start at the most basic level of matter. Atoms are the smallest, simplest structural unit of matter.

An atom is the smallest particle of an element; it is made of three subparticles: electrons, protons, and neutrons.

Elements are substances created when one or more atoms of the same type (for example, nitrogen or oxygen) combine. These are pure substances that cannot be broken down. Pure elements are made of molecules. Molecules are the simplest units of a chemical compound that can exist. They are formed when two or more atoms join together chemically.

Elements are named using a system of chemical symbols. A chemical symbol is a one- or two-letter notation used to represent an atom of a particular element. These chemical symbols are featured prominently on the Periodic Table of Elements. Chemical symbols always begin with a capital letter.

Some symbols consist of two letters, one capital and one lowercase. Below is a table of some common elements and their symbols.

There are about 118 elements currently, with new ones being added as they are discovered. Elements fall into one of three main categories based on their physical properties.

Element Name

Chemical Symbol

Element Name

Chemical Symbol

Carbon

C

Oxygen

O

Silver

Ag

Gold

Au

Silicon

Si

Phosphorus

P

144 | Elements and Compounds

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STEMscopedia subscripts, small numbers below and to the right of them.

These indicate the structure and number of atoms that make up the element. For example, in free oxygen, the element’s structure contains two oxygen atoms bonded together. The chemical symbol for oxygen is O, but since there are two atoms of oxygen in each molecule, you see a subscript indicating that. A subscript is a part of the chemical formula for a compound. Compounds will always have the same subscripts in their chemical formulas. For example, magnesium chloride (MgCl2) will always have the same subscripts since it consists of one magnesium atom chemically bonded to two chlorine atoms.

This is a single molecule of the substance.

If there is only one atom of a given type in a compound, the subscript is one, and it is not written.

For example, in the chemical formula H2O, there are two hydrogen atoms and a subscript of 2 is used.

However, there is only one oxygen atom, and the subscript of 1 is not written.

Changing the subscript within a chemical formula actually changes the identity of the substance. For example, O2 is the oxygen we breathe, but O3 is ozone, a greenhouse gas in Earth’s atmosphere.

Changing the subscript changes the identity of a substance.

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Elements and Compounds | 145

STEMscopedia that e u r t 2. Is it n use a we ca l symbol a chemic ermine to det r we e wheth element an have ompound? or a c why not? or Why

146 | Elements and Compounds

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STEMscopedia Compounds are formed when atoms of different elements combine. A compound is a new substance with unique chemical and physical properties formed when two or more elements are chemically bonded during a chemical reaction. They are represented by chemical formulas. A chemical formula is a shorthand notation that uses chemical symbols and numbers as subscripts to represent the type and number of atoms present in the smallest unit of a substance.

Since a compound consists of more than one element, its formula will have more than one capital letter.

Here is a list of some common compounds. Notice how each compound has more than one capital letter.

Each time you see a capital letter, you have a new element in the compound.

Compound Name

Chemical Symbol

Structure

Sodium chloride

NaCl

One sodium atom, one chlorine atom

Water

H2O

Two hydrogen atoms, one oxygen atom

Ammonia

NH3

One nitrogen atom, three hydrogen atoms

Sulfuric acid

H2SO4

Two hydrogen atoms, one sulfur atom, four oxygen atoms

Chemical formulas reveal the compound’s structure, or arrangement of parts. The atoms depicted in chemical formulas are chemically bonded to one another.

Compounds themselves are not found on the Periodic Table, but the elements composing them are. For example, water is not found on the Periodic Table, but its elements, hydrogen and oxygen, are.

are w o H .

3 ts and n e m ele nds compou t in n differe their of terms ture? struc

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Elements and Compounds | 147

STEMscopedia You can compare and contrast elements and compounds in terms of how they are written. Elements have chemical symbols, such as H2 or Si, but compounds are represented with chemical formulas such as SiO2 or CaCO3.

6RPHWLPHV VFLHQWLVWV XVH D FRHI¿ FLHQW LQ ZULWLQJ D FKHPLFDO IRUPXOD $ FRHI¿ FLHQW is a number placed in front of a chemical symbol or formula that represents the number of molecules. It tells us how many molecules of a given element or compound are involved in a chemical reaction.

S

Fe

Fool’s gold FeS2

S

Fe

S

S

Fe

S

S

2FeS2

On the left of the diagram, there is one molecule of the compound FeS2. On the right, there are two PROHFXOHV RI WKH VDPH VXEVWDQFH &KDQJLQJ WKH FRHI¿ FLHQW LQ D FKHPLFDO IRUPXOD FKDQJHV WKH QXPEHU RI molecules present in the substance as a whole. It does not change the identity of the substance. &KDQJLQJ WKH FRHI¿ FLHQW FKDQJHV WKH QXPEHU RI PROHFXOHV RI D FRPSRXQG LQYROYHG LQ D FKHPLFDO reaction. In a chemical reaction, the number of atoms of each element must be the same before and DIWHU WKH UHDFWLRQ &RHI¿ FLHQWV FDQ EH DGMXVWHG WR PDNH WKLV KDSSHQ

at is 4. Wh rence fe the dif een betw ing a chang t of ip subscr nt or me an ele nd and compou ing a chang QW" LH FRHIŞ F

148 | Elements and Compounds

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STEMscopedia Felycia Edi Soetaredjo Widya Mandala Catholic University Dr. Felycia Edi Soetaredjo is a professor of chemical engineering and the deputy dean of the College of Engineering at Widya Mandala Catholic University in Indonesia. She is an expert on the valorization of biomass, wastewater treatment, and wastewater reuse. She researches methods of converting biomass that may be contaminated with pollutants into energy, fuels, and other material.

One of her goals is to reduce water pollution in Indonesia. She is achieving this by developing a process to treat pollutants in wastewater over a short time to degrade almost all of the compounds that pollute wastewater. She hopes that her methods will make it less expensive for factories to treat their wastewater, and also make them more willing to do so.

In her educational work, she helps support students through a program called Engineers in Action, which allows engineering students in Java to participate in community work alongside students from Indonesia.

Wastewater being released from a factory into a nearby water body after being treated for pollutants.

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Elements and Compounds | 149

STEMscopedia Both elements and compounds are made of atoms. Atoms are the smallest, simplest structural units of matter. Elements are created when one or more atoms of the same type chemically combine. Pure HOHPHQWV DUH PDGH RI DWRPV RI GLIIHUHQW W\SHV FKHPLFDOO\ FRPELQHG LQ ¿ [HG UDWLRV WR IRUP PROHFXOHV When we compare and contrast elements and compounds, we understand that the atoms or molecules all consist of the same thing in an element but can be different combinations of various elements in compounds. Structurally, elements and compounds are different, with compounds being more complex. Elements are represented by chemical symbols, and compounds are represented using chemical formulas.

Connect It Can salt be found on the Periodic Table of Elements?

No, it cannot. Salt is a compound created by two separate elements, sodium and chlorine. Those two individual elements can be found on the table, but not in the form we know as table salt.

150 | Elements and Compounds

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STEMscopedia 1

Which of the following statements is true about elements and compounds?

A The atoms composing elements are all the same type, and the ones composing compounds are different.

B Compounds are less complex in terms of structure than elements.

C Chemical symbols can be used to represent both elements and compounds.

D Chemical formulas are only used for elements but not compounds.

2

Chemical formulas– A FDQ KDYH WKHLU FRHI¿ FLHQWV FKDQJHG ZLWKRXW FKDQJLQJ WKH QXPEHU RI DWRPV WKDW FRPSRVH WKHP B only contain one chemical symbol since they are pure substances.

C can contain more than one chemical symbol since they represent compounds.

D can contain more than one reaction.

3

If a scientist wants to change the number of atoms in a compound without changing the identity of the substance itself, they should– A FKDQJH WKH FRHI¿ FLHQW DW WKH IURQW RI WKH PROHFXOH B change the subscript of one of the elements.

C be sure to change the identity of the atoms in the compound.

D build the molecular model without indicating the subscripts.

4

Fill in the table with the characteristics of elements or compounds that are missing.

Elements Chemical Symbols or Formulas

5

Compounds

Represented by chemical symbols

Represented by ____________________

Atoms and Molecules

Composed of _______ of the same ______

Composed of ______ of different ______

Examples

__________ and __________

___________ and ___________

Which explanation correctly represents the kinds and number of atoms in the compound Na2SO4, or sodium sulfate?

A Four sodium atoms, two sulfur atoms, and four oxygen atoms B Six sodium atoms, one sulfur atom, and six oxygen atoms C One sodium atom, two sulfur atoms, and four oxygen atoms D Two sodium atoms, one sulfur atom, and four oxygen atoms

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Elements and Compounds | 151

Elements and the Periodic Table

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153

STEMscopedia You create your own patterns or ways of organizing things. Maybe you put your clothes away based RQ WKH VHDVRQ WKH\ DUH IRU RU PD\EH \RX RUJDQL]H WKH ¿ OHV RQ \RXU FRPSXWHU EDVHG RQ WKH W\SH RI GRFXPHQW 0RVW RI WKH WKLQJV SHRSOH RUJDQL]H KDYH D VSHFL¿ F V\VWHP EHKLQG LW :KDW DUH VRPH WKLQJV you like to keep organized?

e t is th a h W 1. ge of s a t n a v t ad lemen e e g in keep d using th e organiz dic Table?

Perio

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Elements and the Periodic Table | 155

STEMscopedia The atom is the building block of life, and scientists have developed models for the structure of the atom over time. The time line of the development of the atomic model is seen below: Atomic Model Time Line •

• •

•

1808 – John Dalton: proposed a collection of theories, known as Dalton’s postulates, regarding the atom ƕ Elements are composed of small indivisible particles called atoms. ƕ Atoms of the same element are identical. Atoms of different elements are different. ƕ Atoms of different elements combine together in simple proportions to create a compound. ƕ In a chemical reaction, atoms are rearranged but not changed. Atoms cannot be created or destroyed.

1904 – J. J. Thomson: created the plum pudding model ƕ Thomson discovered that the atom is made up of smaller things. ƕ He theorized that small negative particles (electrons) are embedded in a positive material.

1911 – Ernest Rutherford: conducted the gold foil experiment ƕ Rutherford shot helium alpha particles at a piece of gold foil and noticed that some of the particles bounced back. ƕ He determined that at the center of an atom is a nucleus that houses the protons.

1932 – James Chadwick: discovered neutrons

Due to the hard work of these scientists, we now know that elements are made up of atoms and the atom is composed of protons, neutrons, and electrons. These three particles are known as subatomic particles. Protons, neutrons, and electrons differ from each other based on their locations in an atom and their electrical charge. Protons are in the nucleus, have a positive charge, and have a mass of about 1 amu (atomic mass unit). The neutrons are also located in the nucleus, are neutral (do not have a charge), and have a mass of about 1 amu. Electrons are in the electron cloud that surrounds the nucleus, have a negative charge, and have a mass that is so small that it is considered 0 amu.

Nucleus

Proton

Neutron

Cloud of electrons

Electron 156 | Elements and the Periodic Table

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STEMscopedia

u ould yo w w o m 2. H an ato ? e ib r desc wn words r o in you

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Elements and the Periodic Table | 157

STEMscopedia There are 118 known elements in the world that are made up of atoms. These elements have been placed on the Periodic Table of Elements DQG DUH RUJDQL]HG LQ D VSHFL¿ F ZD\ EDVHG RQ WKH properties of elements. First, it is organized into columns called groups or families, and rows called periods.

The elements are ordered in rows from left to right by increasing atomic numbers. The atomic number is the number of protons in the nucleus of that atom. Each atom of an element always has the same number of protons and therefore the same atomic number. Moving from left to right on each row of the Periodic Table, the atomic number increases in order. For example, the atomic number of carbon (C) is 6, and the atomic number of nitrogen (N) is 7. These elements are next to each other in the second row of the Periodic Table. The atomic number increases as you go to the right across and as you go down the Periodic Table.

Because elements are arranged according to their atomic number, the atomic mass of each element also increases when moving to the right and down the Periodic Table. Atomic mass is the average mass of one atom of an element.

1 1A 1

1

H

hydrogen 1.008 [[1.0078, 1.0082]]

3

2

3

4

5

6

7

Li

2 2A 4

beryllium

6.94 [[6.938, 6.997]]

9.0122

11

12

Mg

sodium

magnesium

22.990

24.305 [[24.304, 24.307]]

19

20

K

Key: atomic number

Symbol

Be

lithium

Na

18 8A

Periodic Table of the Elements

Ca

standard atomic weight

8 3 3B 21

4 4B 22

5 5B 23

Ti

14 4A 6

15 5A 7

16 6A 8

17 7A 9

helium

boron

carbon

nitrogen

oxygen

fluorine

neon

10.81 [[10.806, 10.821]]

12.011 [[12.009, 12.012]]

14.007 [[14.006, 14.008]]

15.999 [[15.999, 16.000]]

18.998

20.180

13

14

15

16

17

B

name

conventional atomic weight

Sc

2

V

6 6B 24

Cr

9

7 7B 25

26

iron

cobalt

Mn

Fe

8B 27

Co

10

Al

C

N

Si

P

O S

F

Cl

silicon

phosphorus

sulfur

chlorine

argon

26.982

28.085 [[28.084, 28.086]]

30.974

32.06 [[32.059, 32.076]]

35.45 [[35.446, 35.457]]

39.948

31

32

33

34

35

nickel

copper

zinc

gallium

germanium

arsenic

selenium

bromine

krypton 83.798(2)

28

Ni

Cu

Zn

Ga

Ge

As

Se

Br

titanium

vanadium

chromium

manganese

39.098

40.078(4)

44.956

47.867

50.942

51.996

54.938

55.845(2)

58.933

58.693

63.546(3)

65.38(2)

69.723

72.630(8)

74.922

78.971(8)

79.904 [[79.901, 79.907]]

37

38

39

40

41

42

43

44

45

46

47

48

49

50

51

52

53

Zr

Nb

Mo

rubidium

strontium

yttrium

zirconium

niobium

85.468

87.62

88.906

91.224(2)

92.906

95.95

55

56

57 - 71

72

73

74

cesium

barium

lanthanoids

132.91

137.33

87

88

89 - 103

radium

actinoids

rutherfordium

Cs Fr

francium

Ba

Ra

Hf

Actinide Series

Pd

Ag

Cd

In

Sn

palladium

silver

cadmium

indium

tin

antimony

tellurium

iodine

xenon

102.91

106.42

107.87

112.41

114.82

118.71

121.76

127.60(3)

126.90

131.29

77

78

79

80

81

82

83

84

85

platinum

Pt

Au gold

mercury

thallium

178.49(2)

180.95

183.84

186.21

190.23(3)

192.22

195.08

196.97

200.59

104

105

106

107

108

109

110

111

112

bohrium

hassium

La

58

Ce

59

Pr

Re

60

praseodymium

138.91

140.12

140.91

144.24

89

90

91

92

thorium

protactinium

uranium

232.04

231.04

238.03

Ac

Th

Pa

Hs

61

Nd

cerium

actinium

Os

Bh

lanthanum

Pm

neodymium promethium

U

54

Xe

rhodium

iridium

Sg

I

76

osmium

seaborgium

Te

101.07(2)

rhenium

Db

Sb

36

Kr

ruthenium

75

tungsten

dubnium

W

Rh

tantalum

57

Lanthanide Series

molybdenum technetium

Ru

hafnium

Rf

Ta

Tc

18

Ar

aluminum

scandium

Y

10

Ne

12 12B 30

calcium

Sr

4.0026

11 11B 29

potassium

Rb

He

13 3A 5

93

Np

neptunium

Ir

Mt

Ds

Rg

Hg Cn

meitnerium darmstadtium roentgenium copernicium

62

Sm

63

Eu

64

Gd

65

Tb

Tl

Pb

Bi

lead

bismuth

204.38 [[204.38, 204.39]]

207.2

208.98

113

114

nihonium

flerovium

Nh

66

Dy

115

Fl

Mc

Po

polonium

116

Lv

moscovium livermorium

67

68

Ho

Er

69

Tm

At

astatine

117

Ts

tennessine

70

Yb

86

Rn

radon

118

Og

oganesson

71

Lu

samarium

europium

gadolinium

terbium

dysprosium

holmium

erbium

thulium

ytterbium

lutetium

150.36(2)

151.96

157.25(3)

158.93

162.93

164.93

167.26

168.93

173.05

174.97

94

95

96

97

98

99

100

101

102

103

nobelium

lawrencium

Pu

plutonium

Am

americium

Cm

curium

Bk

berkelium

Cf

californium

Es

einsteinium

Fm

fermium

Md

mendelevium

Alkali metals

Alkaline earth metals

Lanthanides

Actinides

Transition metals

Poor metals

Metalloids

Nonmetals

Halogens

Noble gases

No

Lr

There are additional patterns of arrangement on the Periodic Table. The vertical columns are known as groups. If you look at the Periodic Table, you will notice that numbers and letters are used to identify JURXSV )RU H[DPSOH WKH ¿UVW JURXS IURP WKH OHIW LV $ (OHPHQWV LQ WKH VDPH JURXS KDYH WKH VDPH number of electrons in the outer energy level, called valence electrons. They determine the chemical behavior of an element. So, elements in the same group have similar chemical properties. These groups share a common method that atoms take when they bond with other atoms. Reactivity is the ability of

158 | Elements and the Periodic Table

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STEMscopedia There are some exceptions to this order, as shown by the unshaded elements in the diagram below.

The arrangement of elements in the Periodic Table is based on atomic number, how the element reacts, and the number of electrons in the outer energy level, allowing you to predict the behavior of elements based on their locations on the table.

se you o p p u r 3. S numbe e h t know tons in an of pro hat other atom. W n would you atio inform in order to s need e mas . h t e in in determ tom? Expla a of the

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Elements and the Periodic Table | 159

STEMscopedia /RRN DW WKH ¿UVW FROXPQ RU *URXS $ RI WKH 3HULRGLF 7DEOH (DFK HOHPHQW LQ WKLV JURXS KDV RQH YDOHQFH electron. Sodium (Na) and potassium (K) are two elements in this group. These elements are metals and tend to donate their single valence electrons to other elements in order to have a full outer energy level.

The other elements in this group also tend to donate their single valence electrons.

11P 12N

20N 19P

Sodium

Potassium

Elements in other groups also have the same number of valence electrons as other elements in their same group. For example, elements in the second column (group) have two valence electrons and tend WR GRQDWH WKHVH WZR HOHFWURQV (OHPHQWV LQ *URXS WKH VHFRQG WR ODVW FROXPQ RQ WKH ULJKW KDYH VHYHQ YDOHQFH HOHFWURQV 7KH\ QHHG RQH HOHFWURQ WR ¿OO WKHLU RXWHU HQHUJ\ OHYHO VR WKH\ WHQG WR UHDFW with other elements to gain one electron. Alternatively, the elements in the last column are known as noble gases. These elements have a full outer energy level with eight valence electrons, so they tend to keep their electrons and are very stable elements. They do not react easily with other elements.

You learned earlier in the lesson that atomic numbers increase as you move from left to right across rows and down the Periodic Table. These rows are called periods, and they correspond to the number of energy levels in an element. Energy levels are the different orbits in which electrons move around the FHQWHU RI DQ DWRP )RU H[DPSOH HYHU\ HOHPHQW LQ WKH WRS URZ ¿UVW SHULRG KDV WKH VDPH QXPEHU RI energy levels. This period contains only two elements: hydrogen (H) and helium (He). These elements have only one energy level. The elements in the second period (Li, Be, B, C, N, O, F, and Ne) have two energy levels. This pattern continues as you move down the rows of the Periodic Table.

160 | Elements and the Periodic Table

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STEMscopedia Marie Curie

Marie Curie (1867–1934) was a Nobel Prize winner in both Physics and Chemistry during her lifetime.

Marie came from a family of educators that believed in the importance of education, so after completing her basic education she moved to Paris to continue her studies. That is where she met her husband, Pierre Curie. The couple worked together to examine substances for signs of radioactivity. Through their investigations, they were able to discover two radioactive elements: polonium and radium. After the death of Pierre in 1906, Marie continued with their investigations. In 1910, Marie produced radium as a SXUH PHWDO ZKLFK VROLGL¿ HG WKH H[LVWHQFH RI UDGLXP DV DQ HOHPHQW 7KHVH GLVFRYHULHV KDYH JRQH RQ WR EH LPSRUWDQW LQ WKH ¿ HOG RI PHGLFLQH SDUWLFXODUO\ IRU WKH WUHDWPHQW RI FDQFHU

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Elements and the Periodic Table | 161

STEMscopedia $Q DWRP LV FRPSRVHG RI WKUHH VXEDWRPLF SDUWLFOHV SURWRQV QHXWURQV DQG HOHFWURQV :LWKLQ DQ DWRP the protons and neutrons are in the nucleus and the electrons are in the electron cloud that surrounds the nucleus. Atoms make up all the elements on the Periodic Table. The Periodic Table arranges the elements, and we can use it to predict physical and chemical properties such as size, mass, conductivity, and reactivity.

Connect It What is the advantage of keeping the elements organized using the Periodic Table?

As we discovered throughout the text, the Periodic Table provides us with information about each element based on its location on the table. This also provides information about the behavior of each element.

y is it h W . w 4 to k no t n a t mpor ysical and im h the p properties al chemic element? of an

162 | Elements and the Periodic Table

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STEMscopedia 1

:KLFK WZR SDUWLFOHV FRPELQH WR PDNH XS WKH PDVV RI DQ HOHPHQW" A Electrons and protons B Neutrons and protons C Electrons and neutrons D None of the above

2

All the elements in the universe are made of _________________. Each of those atoms are made up of three smaller _________________.

3

:KLFK VWDWHPHQW LV WUXH DERXW WKH 3HULRGLF 7DEOH" A The Periodic Table is organized by physical properties.

B The Periodic Table is organized by atomic weight.

C The Periodic Table is organized by date of discovery.

D The Periodic Table is organized by atomic mass.

4

Select two correct answers. Atomic mass of an element generally increases as– A you go up a group on the Periodic Table.

B you go down a group on the Periodic Table.

C you go left to right across the Periodic Table.

D you go right to left across the Periodic Table.

5

How do the numbers of protons and electrons in an atom affect its electrical charge?

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Elements and the Periodic Table | 163

Metals, Nonmetals, and Metalloids

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165

STEMscopedia Have you ever wondered why certain insulated cups are better at keeping beverages hotter than others? Or why electrical wires are mostly made of the same elements? It has to do with their physical properties. Similarly, snow will melt on both a plastic plate and a metal one, but it will melt much faster RQ D PHWDO SODWH WKDW KDV EHHQ KHOG LQ \RXU KDQG RU NHSW QHDU D FDPS¿ UH :K\"

1. W determ hat in fast ic es how on plaa e melts tes of diff made er mater ent ials?

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Metals, Nonmetals, and Metalloids | 167

STEMscopedia Physical properties are characteristics or properties that can be observed or measured without changing the substance. This includes observations involving color, size, and volume. Three physical properties are helpful when identifying the composition of a substance.

Conductivity LV D SK\VLFDO SURSHUW\ WKDW LGHQWL¿ HV ZKHWKHU D VXEVWDQFH FDQ WUDQVIHU KHDW RU HOHFWULFDO energy. Substances can be either conductors, like metal wires, or insulators, like the material inside of your winter coat. If an item is a conductor, it will generally conduct heat and electricity. Many metal substances, like copper and iron, are conductors.

Heat is used to weld different metal pieces together. Conductivity of heat is one physical property that can be used to identify metal substances. Metals usually have a shiny luster DQG UHÀ HFW OLJKW Luster is another physical property that can be easily observed. It describes the way the surface of a VXEVWDQFH VKLQHV RU UHÀ HFWV OLJKW ,W LV XVHIXO LQ GHWHUPLQLQJ ZKHWKHU D VXEVWDQFH PLJKW EH D PHWDO Metallic substances tend to have shiny or glassy lusters. Nonmetallic substances have duller lusters and GR QRW UHÀ HFW OLJKW

168 | Metals, Nonmetals, and Metalloids

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STEMscopedia

These chrome manufacturing nuts have a shiny luster, as most metals do.

7KHLU PHWDOOLF FRPSRVLWLRQ FDXVHV WKHP WR UHÀ HFW OLJKW DQG JLYHV WKHP D VKLQ\ OXVWHU Malleability is another physical property that can be used to identify a substance as a metal or nonmetal. An element that is malleable is able to be hammered or pressed into a thin sheet.

An example of this is aluminum foil.

2. Imagine you have a substance with a shiny luster and high malleability.

Name an original item you could create with it, and explain how the physical properties of this item make it useful for your creation.

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Metals, Nonmetals, and Metalloids | 169

STEMscopedia The Periodic Table of Elements organizes all known elements into rows (periods) and columns (groups).

Elements are pure substances composed of the same kind of atom throughout. They cannot be broken down. Examples of elements are carbon, oxygen, and aluminum. Elements in the same group on the Periodic Table tend to behave the same way.

Metals

Metalloids

Nonmetals

The Periodic Table of Elements contains one box for each of the known elements. There are three main types of elements—metals, nonmetals, and metalloids.

3. Doe s you tha it surprise are be t metalloids and no tween metals n Periodic metals on th e Table?

W or why hy not?

170 | Metals, Nonmetals, and Metalloids

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STEMscopedia Metals are the elements that make up most of the Periodic Table. There are 88 metals, and they are grouped together on the left of the Periodic Table. Metals have a shiny luster, are good conductors, and are malleable. They have a high melting point and are ductile, meaning that they can be pulled into long wires for circuits or other uses.

Metals

Metalloids

Metals

Nonmetals

• Most elements are metals.

• These are found on the left side of the Periodic Table.

• All but one of these metals are solids •

at room temperature.

Examples are iron, copper, zinc, silver, gold, mercury, and uranium.

Let’s look at aluminum for an example. This is a metal used in a variety of common objects, including IRRG FDQV DLUSODQH SDUWV ODGGHUV FDU SDUWV DQG HOHFWURQLFV ,W LV D JRRG UHÀ HFWRU DQG FDQ EH UHXVHG multiple times.

You might be familiar with aluminum foil. It can be bent and molded into almost any shape. This is PDOOHDELOLW\ ,W DOVR UHÀ HFWV OLJKW DQG FRQGXFWV KHDW 7KLQN RI D PHWDO VOLGH DW D SDUN ,W LV OLNHO\ PDGH RI aluminum or another metal.

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Metals, Nonmetals, and Metalloids | 171

STEMscopedia are a subset of metals. There are 17 metallic elements that are considered rare earth elements. Of these elements, 15 are in a line beneath the Periodic Table called the lanthanide series. The other two, scandium and yttrium, are located within the metals on the Periodic Table. Even though the name says they are rare, they are not rare in amount. Rare earth elements are plentiful in Earth’s crust, but they are spread out around the planet. Because of their locations, they are not easy to mine, which led them to have this name.

5DUH HDUWK HOHPHQWV KDYH XQLTXH SURSHUWLHV VXFK DV EHLQJ PDJQHWLF À XRUHVFHQW XQGHU 89 OLJKW DQG electrochemical. This makes them a great choice for many modern-day electronics. Rare earth elements are used in smartphones, cameras, computers, electric cars, high-powered magnets, solar panels, batteries, and more.

H

He

Rare Earth Elements

Be

B

C

N

O

F

Ne

Na Mg

Al

Si

P

S

Cl

Ar

Cu Zn Ga Ge As

Se

Br

Kr

Li

K

Ca Sc

Ti

V

Cr Mn Fe Co

Ni

Rb Sr

Y

Zr

Nb Mo

Tc Ru Rh Pd Ag Cd

ln

Sn Sb Te

l

Xe

Cs Ba

*

Hf

Ta

Re Os

Tl

Pb

At

Rn

Fr

**

Rf

Db Sg Bh Hs Mt

Ra

W

*

La

Ce Pr

**

Ac Th Pa

Ir

Pt

Au Hg

Ds Rg Cn Uut

Nd Pm Sm Eu Gd Tb U

Light Rare Earth Elements

172 | Metals, Nonmetals, and Metalloids

Po

Fl Uup Lv Uus Uuo Er Tm Yb

Lu

Es Fm Md No

Lr

Dy Ho

Np Pu Am Cm Bk Cf

Bi

Heavy Rare Earth Elements

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STEMscopedia are the opposite of metals. They are the most abundant elements on Earth.

They are not shiny and do not conduct heat and electricity. They are brittle, meaning that if they are hammered, they are likely to crack or break apart instead of bending. Nonmetals are grouped together on the right side of the Periodic Table of Elements.

Metals

Metalloids

Nonmetals

Nonmetals

• These are the most abundant elements.

• They are found on the right side of the Periodic Table.

• Many are gases at room temperature.

• Most nonmetals are NOT malleable, NOT shiny, NOT ductile, and NOT good conductors of heat and electricity.

The gaseous elements are nonmetals, such as oxygen and nitrogen. Fertilizers, soft materials for clothing, and gases used as refrigerants are nonmetals. They also make great insulating material for clothing and food storage.

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Metals, Nonmetals, and Metalloids | 173

STEMscopedia Metalloids share some properties of both metals and nonmetals. For instance, some may look like metals but act like nonmetals. They can be semiconductors of heat and energy, but they do not conduct either as well as metals do. They fall somewhere between conductors and nonconductors. Some metalloids are brittle while others are malleable. They can be found on either side of the stair step of the Periodic Table, which is a line that looks like a stair step. You may have heard of some of them, such as silicon and selenium.

Metals

Metalloids

Metalloids

Nonmetals

• They are located along a zigzag • • • •

line between the metals and nonmetals.

Metalloids are also known as semiconductors.

They possess some of the properties of both metals and nonmetals.

8VXDOO\ WKH\ DUH KDUG and brittle.

Six commonly recognized metalloids are boron, silicon, germanium, arsenic, antimony, and tellurium.

4. Wh y think do you are fo metals abunda und more ntly core o in the f as opp Earth o the su sed to rface?

174 | Metals, Nonmetals, and Metalloids

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STEMscopedia Alan Williams Metal Sculptor $ODQ :LOOLDPV LV DQ (QJOLVK PHWDO VFXOSWRU ZKR ZRUNV RXW RI %ULJKWRQ (QJODQG +H XVHV UHF\FOHG materials to make sculptures of land and sea creatures, including chameleons and birds. He became LQWHUHVWHG LQ ZHOGLQJ ZKHQ KH ZDV DIWHU ZDWFKLQJ DQ DUWLVW RQ 79 PDNH D VFXOSWXUH IURP PHWDO :LOOLDPV¶V XQLTXH FUHDWLRQV LQFOXGLQJ D OLIH VL]H UKLQRFHURV KDYH EHHQ PDGH IURP D YDULHW\ RI IRXQG DQG recycled metal, including kitchen cutlery. His metalworks have been featured at exhibitions throughout (QJODQG DQG )UDQFH DQG KLV ZRUN KDV EHHQ IHDWXUHG RQ WKH 79 VKRZ Grand Designs as well as Bored Panda and Gizmodo.

$ \RXQJ $ODQ :LOOLDPV ZDV LQWHUHVWHG LQ ZHOGHUV¶ SURWHFWLYH HTXLSPHQW DV KH ZDWFKHG D PHWDO VFXOSWXUH EHLQJ FUHDWHG RQ D 79 VKRZ 1RZ :LOOLDPV PDNHV VFXOSWXUHV DQG GLVSOD\V RXW of recycled metal for art exhibitions in England and France.

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Metals, Nonmetals, and Metalloids | 175

STEMscopedia The Periodic Table of Elements organizes the known elements by their physical properties and behavior.

There are three main groups of elements: metals, nonmetals, and metalloids. Metals have a shiny luster DQG UHÀ HFW OLJKW 7KH\ DOVR KDYH KLJK FRQGXFWLYLW\ DQG PDOOHDELOLW\ 1RQPHWDOV KDYH D GXOO OXVWHU GR QRW conduct heat and electricity, and have a tendency to break rather than to be reshaped. Metalloids share properties of both metals and nonmetals and are usually called semiconductors.

Connect It Why does a metal plate melt ice more quickly than a plastic one?

To address this question, we must consider the heat conductivity of both the metal and nonmetal plates.

The physical properties of the plates determine how well they conduct heat. The heat from your hand or WKH ¿ UH ZLOO ZDUP WKH PHWDO SODWH DQG WKH LFH PXFK PRUH TXLFNO\ EHFDXVH WKH PHWDO SODWH LV D FRQGXFWRU +HDW HQHUJ\ ZLOO WUDYHO TXLFNO\ DQG HI¿ FLHQWO\ WKURXJK LW 7KH QRQPHWDOOLF SODVWLF SODWH ZLOO QRW FRQGXFW heat as well.

176 | Metals, Nonmetals, and Metalloids

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STEMscopedia 1

:KDW SK\VLFDO SURSHUWLHV ZRXOG EH XVHIXO LQ GHWHUPLQLQJ ZKHWKHU D VXEVWDQFH LV D metal or nonmetal?

A Malleability, conductivity, and luster B Malleability, luster, and color C Texture, color, and shape D Luster, magnetism, and volume

2

Most nonmetals are different from metals because they– A have a shiny luster and do not conduct electricity.

B conduct electricity and are malleable.

C do not conduct electricity and are not malleable.

D are brittle and malleable.

3

$ VWXGHQW ZDQWHG WR GHWHUPLQH LI D FHUWDLQ VXEVWDQFH ZDV D PHWDO QRQPHWDO RU PHWDOORLG :KLFK RI the following would NOT be helpful in making this determination?

A Determining the volume of the substance B Determining its location on the Periodic Table C Determining whether the material has a shiny luster D Hammering the material to see if it is malleable

4

Malleability describes the ability of a substance to be pounded with a hammer to form thin sheets.

8VLQJ WKHLU ORFDWLRQ RQ WKH 3HULRGLF 7DEOH ZKLFK RQH RI WKHVH HOHPHQWV LV PRVW OLNHO\ 127 PDOOHDEOH" A A substance in the middle of the Periodic Table with the rest of the metalloids B A substance located on the right side of the Periodic Table with other elements that have a shiny luster and are conductors C A substance located on the right side of the Periodic Table with other elements that are semiconductors D A substance located on the right side of the Periodic Table with other elements that have a dull luster uster and are not conductors

5

:KLFK RI WKH IROORZLQJ VWDWHPHQWV DFFXUDWHO\ GHVFULEHV WKH GLIIHUHQFH EHWZHHQ WKH SK\VLFDO properties of metals and nonmetals and their locations on the Periodic Table?

A Nonmetals have a shiny luster and are located on the right side of the Periodic Table.

B Nonmetals are located in the middle of the Periodic Table and are semiconductors.

C Metals are on the left side of the Periodic Table and have conductivity.

D Metals are on the right side of the Periodic Table and do not have conductivity.

6

Imagine you were given two mystery substances and asked to determine which of them was a metal and which was a nonmetal. Describe two tests you could do to determine their physical properties and thus their identities as metals, nonmetals, or metalloids.

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Metals, Nonmetals, and Metalloids | 177

Aqueous Solutions

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179

STEMscopedia Swimming pools often have a distinct smell. This comes from a substance called chlorine that is used to treat swimming pool water. Chlorine usually comes in tablets or powder and dissolves in the pool water.

It keeps the pool sparkling clean. Have you ever wondered whether a solid chlorine tablet or powdered chlorine would dissolve more quickly in a pool? What could affect the way these substances behave when mixed with water?

solves is d h 1. Whic a cup of — faster powder e chlorin ith pool w mixed a chlorine or i to water dropped in tablet ter? Why? a pool w

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Aqueous Solutions | 181

STEMscopedia There are two parts to any solution—the substance that dissolves and the substance that something is GLVVROYHG LQWR 7KH ¿ UVW RQH LV D VROXWH $ solute is a substance that dissolves into another substance to form a homogeneous mixture. The salt crystals we put into boiling water to make pasta are examples of VROXWHV 6ROXWHV FDQ EH JDVHV VROLGV RU RWKHU OLTXLGV ,Q WKLV H[DPSOH ZDWHU LV D VROYHQW $ solvent is a substance in which another substance is dissolved to form a homogeneous mixture.

0RVW RI WKH VROXWLRQV \RX FDQ WKLQN RI DUH DTXHRXV VROXWLRQV $Q aqueous solution is any solution in which the solvent is water. When any substance dissolves in water, we note that by using (aq) after its QDPH 6DOW ZDWHU VRGD DQG UDLQ DUH H[DPSOHV RI DTXHRXV VROXWLRQV $OO ELRORJLFDO UHDFWLRQV WDNH SODFH LQ water, since water is necessary for life.

Simply containing water is not enough for a solution to be aqueous. For example, if we mix sand and water together, we do not create an aqueous solution since the solute does not dissolve in the water. The sand retains its identity as it mixes with the water, and it does not form an aqueous solution.

e y ou in g a m 2. I ttle of o b a had drink d e r e powd water in d mix an ch. What n your lu e solute is th olution? s in this is the What t? solven

182 | Aqueous Solutions

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STEMscopedia You may have heard of concentrated liquids, such as laundry or dish detergent. Concentration is D PHDVXUHPHQW RI WKH DPRXQW RI VROXWH WKDW LV GLVVROYHG LQ D JLYHQ TXDQWLW\ RI VROYHQW $ VWURQJHU concentration of an aqueous solution has more solute in it than one that is considered weaker.

Lemonade made from a powdered lemonade mix and water is an aqueous solution where we can taste the difference in concentration. Lemonade with more solute dissolved in the solvent will taste much stronger than a solution with less solute in it.

Concentrated and Diluted Solutions

Concentrated solution

Diluted solution

We can dilute a strong aqueous solution by adding more water. This process is called dilution. Dilution is the process of reducing the ratio of solute to solvent in a solution.

at 3. Wh the ns to happe ration of t concen d laundry re powde gent as deter mixed is water it? with

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Aqueous Solutions | 183

STEMscopedia $ VWXGHQW KDV D EHDNHU RI SXUH ZDWHU LQ WKH ODE 7KH\ DGG D WHDVSRRQ RI VXJDU DQG LW GLVVROYHV 7KH\ continue adding the solute, one teaspoon at a time, until they notice that no more sugar is dissolving. $IWHU VWLUULQJ WKH VXEVWDQFH WKH\ QRWLFH WKDW WKHUH DUH VWLOO VXJDU FU\VWDOV LQ WKH ZDWHU :KDW¶V JRLQJ RQ" Only so much solute will dissolve into a solvent. Once the substance is holding as much solute DV LW FDQ LW LV VDWXUDWHG $ VROXWLRQ WKDW KROGV OHVV VROXWH WKDQ FDQ EH GLVVROYHG LQ LW LV FDOOHG DQ unsaturated solution. $ saturated solution contains the maximum amount of solute for a given amount of solvent at a constant temperature and pressure. If the temperature or pressure of the solution changes, it may affect how much solute can dissolve, changing the saturation. For instance, substances that are hotter, such as those on a stove, will hold more solute before becoming saturated than substances that are cooler.

You can tell if a solution is saturated by the behavior of the solute. If you add a solute to an aqueous solution and it does not dissolve, the solution is saturated.

an you c w o 4. H en an h w ll e t solution s u o e u aq rated? u t a s is

184 | Aqueous Solutions

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STEMscopedia $ VXEVWDQFH¶V rate of dissolution is the speed at which the solute spreads out uniformly into the solvent. We could say it is the rate of dissolving. Three main factors affect how fast a solid solute will dissolve in an aqueous solution—temperature, surface area, and agitation.

7KUHH PDLQ WKLQJV DIIHFW D VXEVWDQFH¶V UDWH RI GLVVROXWLRQ²WHPSHUDWXUH VXUIDFH DUHD and agitation.

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Aqueous Solutions | 185

STEMscopedia ZDWHU )RU LQVWDQFH KRW FRFRD SRZGHU GLVVROYHV IDVWHU LQ ZDWHU LI \RX KHDW XS WKH ZDWHU ¿ UVW 7KLV LV because temperature affects dissolution rates in an aqueous solution. In the same manner, powdered hummingbird nectar will dissolve more quickly if mixed with warm water than if it is mixed with cooler water. This is not the case with gases mixing with water, however; the solubility of a gas actually decreases as the solvent is warmed.

This has important effects on wildlife living in watery environments near factories. Thermal energy in some solutions, like waste from factories, makes the solution release dissolved oxygen more quickly.

7KLV GHFUHDVHV WKH GLVVROYHG R[\JHQ DYDLODEOH WR ¿ VK DQG RWKHU XQGHUZDWHU DQLPDOV VLQFH WKH R[\JHQ is released into the atmosphere from the heated water. This is one way that heat and solubility have a direct effect on wildlife.

Temperature is the average kinetic energy of all the particles in a material. It is measured by a WKHUPRPHWHU LQ GHJUHHV XVXDOO\ GHJUHHV &HOVLXV RU GHJUHHV )DKUHQKHLW 7KH KLJKHU D VXEVWDQFH¶V kinetic energy, the higher the temperature, and the more rapidly a solid solute will dissolve in a solvent.

The molecules in the solute are held together by chemical bonds and stick to each other. The more kinetic energy a substance has, the more easily the molecules can break those bonds, so the substance will dissolve more quickly.

Surface area is a second factor affecting dissolution rates. Surface area is the exposed area of a solid, usually expressed as squared units of length. Powdered substances have more exposed surface area than solid ones. For example, a 2.2 g sugar cube has less surface area than a pile of 2.2 g of loose sugar. Which one do you think will dissolve faster in water?

186 | Aqueous Solutions

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STEMscopedia

The loose sugar will dissolve more quickly because it has more surface area to interact with the solvent.

This is the reason why crushing a solid solute will help it dissolve more quickly in water. In this example, crushing a sugar cube will help it dissolve faster in the water because it would allow more of the sugar to contact the water molecules at the same time. Bouillon cubes work the same way in water. Crushing them increases the surface area, so they will dissolve faster in water.

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Aqueous Solutions | 187

STEMscopedia

CANDY

DQG HIIHUYHVFHQW ¿ ]]\ FDQG\ ,Q WKLV SK\VLFDO UHDFWLRQ WKH JDVHV LQ WKH FDQG\ FRPH LQWR FRQWDFW ZLWK the soda molecules and carbon dioxide gas is released from the top of the solution in a rather dramatic eruption. What do you think would be the effect of crushing the candy before putting it in the soda?

+

=

Finally, agitation can also affect how quickly a solute dissolves in water. Agitation is the stirring or PL[LQJ RI D VROXWLRQ VR DV WR LQFUHDVH WKH SDUWLFOH PRYHPHQW RI WKH VROXWH SDUWLFOHV LQ VROXWLRQ $JLWDWLRQ allows all of the molecules of the solvent to be in contact with the solute molecules. It makes it easier for the solute to dissolve.

ld at wou t h W .

5 effec e h t n be hing a s u r c t of escen v r e f f e before t le b ta into a it g in t put pure f o r e containn ater? w

188 | Aqueous Solutions

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STEMscopedia Dean Mitchell Watercolor Artist Watercolor artist Dean Mitchell likes to portray people and places of his time in his art. He has received more than 400 awards for his work, including ones from the National Watercolor Society and the $PHULFDQ :DWHUFRORU 6RFLHW\ +LV ZRUN RIWHQ UHÀ HFWV KLV XSEULQJLQJ DV DQ XQGHUSULYLOHJHG SHUVRQ ZKR JUHZ XS ZLWKRXW D IDWKHU LQ KLV OLIH $IWHU HQWHULQJ D QDWLRQDO ZDWHUFRORU VKRZ KH EHFDPH RQH RI WKH \RXQJHVW PHPEHUV RI WKH $PHULFDQ :DWHUFRORU 6RFLHW\ DW DJH Watercolors are made with water-soluble pigments dissolved in water. By adding more or less water to a watercolor pigment, Mitchell and other artists can control the concentration of the pigment in the water and the appearance of their paintings.

Watercolor painting involves adjusting the concentration of color by changing the amount of water DGGHG WR D VROXWLRQ $ KLJKHU FRQFHQWUDWLRQ RI SLJPHQW UHVXOWV LQ D PRUH YLVLEOH FRORU ZKLOH D ORZHU concentration of pigment results in more transparent paint.

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Aqueous Solutions | 189

STEMscopedia There are two parts to any solution—the substance that dissolves, or the solute, and the substance that VRPHWKLQJ LV GLVVROYHG LQWR FDOOHG D VROYHQW $Q DTXHRXV VROXWLRQ LV DQ\ VROXWLRQ LQ ZKLFK WKH VROXWH LV dissolved in water.

Concentration is a measurement of the amount of solute that is dissolved in a given quantity of solvent. $ VWURQJHU FRQFHQWUDWLRQ RI DQ DTXHRXV VROXWLRQ KDV PRUH VROXWH LQ LW WKDQ RQH WKDW LV FRQVLGHUHG weaker. Dissolution rate is the speed at which the solute spreads out uniformly into the solvent. Three main factors affect how fast a solid solute will dissolve in an aqueous solution—temperature, surface area, and agitation.

Connect It How can we change the way powdered chlorine and chlorine tablets behave when mixed in pools?

Powdered chlorine has a much larger surface area than a chlorine tablet, so it has a faster dissolution rate than a chlorine tablet. Temperature also affects dissolution rates—warmer pool water will cause solid chlorine to dissolve faster than cooler water. We can affect the dissolution rate of chlorine in water E\ DJLWDWLQJ LW XVXDOO\ ZLWK D SRRO ¿ OWHU

190 | Aqueous Solutions

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STEMscopedia 1

If a student wants to decrease the concentration of an aqueous solution, what should be done?

A The student should add more solvent to the solution.

B The student should add more solute to the solution.

C The student should agitate the solution.

D The student should decrease the surface area of the solution.

2

What is the effect of agitating a solution of protein powder and drinking water?

A 6WLUULQJ GHFUHDVHV WKH GHQVLW\ RI WKH SURWHLQ SRZGHU PDNLQJ LW À RDW B $JLWDWLRQ GHFUHDVHV WKH VXUIDFH DUHD RI WKH VROXWH C $JLWDWLRQ KHOSV GHFUHDVH WKH FRQFHQWUDWLRQ RI WKH VROXWLRQ D Stirring the solution helps increase the rate of dissolution.

3

$ VWXGHQW LQ D ODERUDWRU\ ZDQWV WR LQFUHDVH WKH FRQFHQWUDWLRQ RI VDOW LQ VDOW ZDWHU :KDW LV RQH FRUUHFW way to achieve this effect?

A )UHH]H WKH VROXWLRQ ZKLFK LQFUHDVHV WKH YROXPH RI WKH VROXWLRQ B $JLWDWH WKH VROXWLRQ C Heat the solution, causing some of the solvent to evaporate.

D $GG PRUH ZDWHU WR WKH VROXWLRQ WR GLOXWH LW

4

Identify the solute and the solvent in the following aqueous solutions.

Solution

Solute

Solvent

Orange juice Tea Pool water Vinegar (acetic acid) 5

Which of the following choices describes an investigation in which a student is studying the effect of increasing the surface area of a solute?

A $ VWXGHQW PL[HV VRGLXP FKORULGH LQ YDULRXV YROXPHV RI ZDWHU DQG FDOFXODWHV WKH FRQFHQWUDWLRQ RI each solution.

B $ VWXGHQW GURSV D VXJDU FXEH LQ ZDWHU DQG PL[HV D WDEOHVSRRQ RI ORRVH VXJDU LQ D VHFRQG container of water to see which one dissolves more quickly.

C $ VWXGHQW SRXUV D VLQJOH FRQWDLQHU RI VDOW ZDWHU RQ WKH ODE FRXQWHU DQG PHDVXUHV KRZ ORQJ LW takes to evaporate.

D $ VWXGHQW PL[HV D WHDVSRRQ RI FRSSHU VXOIDWH LQWR HDFK RI WZR LGHQWLFDO EHDNHUV RI ZDWHU DQG VWLUV them at different speeds to see which one dissolves more quickly.

6

Describe an investigation that could help a student model how temperature affects the rate of dissolution in a solid. Describe the results that you would expect.

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Aqueous Solutions | 191

Relative Density

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193

STEMscopedia Imagine a day on vacation at the beach. You spend time both in the ocean and in the swimming pool. :KHQ \RX DUH LQ WKH RFHDQ \RX QRWLFH WKDW \RX À RDW HDVLO\ DQG KLJKHU LQ WKH VDOW ZDWHU RI WKH RFHDQ ,W¶V DOVR KDUG WR VWD\ XQGHU WKH VXUIDFH ,I \RX JR WR D VZLPPLQJ SRRO WKRXJK \RX QRWLFH WKDW \RX KDYH DQ HDVLHU WLPH VWD\LQJ XQGHU WKH VXUIDFH DQG \RXU ERG\ GRHV QRW À RDW DV HDVLO\ DV LQ WKH RFHDQ +DYH \RX ever wondered why?

can 1.. Why PRUH DW \RX ş R in the a y il s a e an in h t n a oce g pool? in m im sw

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Relative Density | 195

STEMscopedia Density LV WKH DPRXQW RI PDWWHU LQ D JLYHQ VSDFH RU YROXPH ,I PRUH PDWWHU LV SDFNHG LQWR D VSDFH ZH VD\ LW LV PRUH GHQVH RU KDV PRUH GHQVLW\ ,I OHVV PDWWHU LV SDFNHG LQWR WKH VDPH VSDFH ZH VD\ LW LV OHVV dense or has less density. Density is not the same as weight, although they are related.

7R XQGHUVWDQG ZKDW GHQVLW\ LV OHW¶V ORRN DW SXUH ZDWHU DQG FRPSDUH LW WR JROG 0DVV LV PHDVXUHG LQ grams (g), and volume is measured in cubic centimeters (cm3) or milliliters (mL). One cubic centimeter LV WKH VDPH DV RQH PLOOLOLWHU P/ RI À XLG 'HQVLW\ LV IRXQG E\ GLYLGLQJ WKH PDVV E\ WKH YROXPH 7KH GHQVLW\ RI ZDWHU LV J FP3 7KH GHQVLW\ RI JROG KRZHYHU LV PXFK JUHDWHU ,W LV J FP3. This means WKDW JROG KDV PXFK PRUH PDWWHU SDFNHG LQWR RQH FXELF FHQWLPHWHU RI VSDFH WKDQ ZDWHU GRHV

:DWHU DQG RWKHU OLTXLGV DV ZHOO DV JDVHV DUH FDOOHG À XLGV $ À XLG LV DQ\ VXEVWDQFH WKDW LV FDSDEOH RI À RZLQJ DQG FKDQJLQJ LWV VKDSH %RWK OLTXLGV DQG JDVHV KDYH HQRXJK VSDFH EHWZHHQ WKHLU PROHFXOHV WR EH DEOH WR À RZ 7KLV SURSHUW\ DOVR PDNHV WKHP OHVV GHQVH WKDQ VROLGV LQ PRVW FDVHV

2. De the tw scribe o prope physical rt determ ies that GHQVLW\ ine the RI D ş XLG

196 | Relative Density

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STEMscopedia Two physical properties that determine density are mass and volume. $LU KDV PDVV HYHQ WKRXJK ZH FDQQRW VHH LW $V \RX NQRZ DQ REMHFW¶V mass LV WKH DPRXQW RI PDWWHU LQ DQ REMHFW $OO PROHFXOHV DUH QRW WKH VDPH VL]H VRPH DUH ODUJHU WKDQ RWKHUV 7KH VL]H RI WKH PROHFXOHV LQ WKH PDWWHU DORQJ ZLWK KRZ PXFK VSDFH WKHUH LV EHWZHHQ WKH PROHFXOHV GHWHUPLQHV WKH PDVV RI DQ REMHFW

PRUH WLJKWO\ WRJHWKHU LQ WKH VDPH VSDFH WKDQ PROHFXOHV LQ D JDV 7KLV PDNHV OLTXLG ZDWHU PRUH GHQVH WKDQ JDVHRXV ZDWHU YDSRU 7KHUH DUH IHZHU PROHFXOHV RI ZDWHU YDSRU LQ WKH same space.

0RVW JDVHV DUH OHVV GHQVH WKDQ OLTXLGV EHFDXVH WKHUH LV VR PXFK VSDFH EHWZHHQ WKH PROHFXOHV )RU example, water is more dense than air because it has less space between each molecule and its neighbor. Gases have much more space between the molecules, allowing them to be less dense. Less matter is in the same space in a gas.

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Relative Density | 197

STEMscopedia LV D PHDVXUH RI WKH VSDFH WKDW PDWWHU RFFXSLHV ,Q WKH LPDJH DERYH WKH YROXPH LV WKH VDPH IRU ERWK WKH ZDWHU DQG WKH JDV PROHFXOHV 9ROXPH LV PHDVXUHG LQ WZR ZD\V )RU REMHFWV ZLWK D UHJXODU RU V\PPHWULFDO VKDSH YROXPH LV IRXQG E\ PXOWLSO\LQJ DQ REMHFW¶V OHQJWK ZLGWK DQG KHLJKW )RU LUUHJXODU REMHFWV WKH SURFHVV RI ZDWHU GLVSODFHPHQW LV XVHG 7KLV LV WKH SURFHVV RI SODFLQJ D JLYHQ DPRXQW RI ZDWHU LQ D JUDGXDWHG F\OLQGHU GURSSLQJ LQ DQ REMHFW DQG PHDVXULQJ WKH FRPELQHG YROXPH RI WKH ZDWHU DQG WKH REMHFW 7KH GLIIHUHQFH EHWZHHQ WKH RULJLQDO UHDGLQJ DQG WKH QHZ UHDGLQJ LV WKH YROXPH RI WKH LUUHJXODU REMHFW

1 mL

10 mL 5 mL

,PDJLQH \RX KDYH D JODVV MDU DQG ¿ OO LW ZLWK URFNV 7KH YROXPH LV WKH DPRXQW RI VSDFH DYDLODEOH WR WKH URFNV :KHQ WKH URFNV ¿ OO WKH MDU QR PRUH VSDFH LV DYDLODEOH IRU WKH URFNV +RZHYHU \RX FDQ DGG PRUH PDWWHU WR WKH MDU ,I \RX DGG VDQG WR WKH MDU LW ZLOO ¿ OO WKH VSDFHV EHWZHHQ WKH URFNV ZLWKRXW PDNLQJ WKH JODVV MDU DQ\ ELJJHU <RX DUH ¿ WWLQJ PRUH PDWWHU LQWR WKH VDPH DPRXQW RI VSDFH ZKLFK ZLOO LQFUHDVH WKH RYHUDOO PDVV EXW QRW WKH YROXPH RI WKH VXEVWDQFH

3. Wh ic think h do you dense is more — rocks a jar of or of roc a jar k sand? s and Why?

198 | Relative Density

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STEMscopedia 'HQVLW\ FDQ EH GHWHUPLQHG E\ FRPSDULQJ WKH PDVV RI DQ REMHFW RU VXEVWDQFH WR WKH DYDLODEOH YROXPH 7R GHWHUPLQH GHQVLW\ \RX GLYLGH WKH PDVV RI DQ REMHFW E\ WKH YROXPH LW RFFXSLHV 7KH KLJKHU WKH GHQVLW\ WKH PRUH PDWWHU LV SDFNHG LQ WKH REMHFW

Foam 0.03 g/cm3 Less dense

Wood 0.8 g/cm3

Concrete 2.5 g/cm3 More dense

mass D = m Density = v volume

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Relative Density | 199

STEMscopedia ¿ QGLQJ GHQVLW\

Mass of jar with rocks: 3,250 g Volume: 950 cm³

Mass of jar with rocks and sand: 5,250 g Volume: 950 cm³

Density: 3.4 g/cm³

Density: 5.5 g/cm³

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3XUH ZDWHU KDV D GHQVLW\ RI J FP3 6DOW ZDWHU KRZHYHU KDV D GLIIHUHQW GHQVLW\ $ YROXPH RI FP3 RI VDOW ZDWHU FRXOG KDYH D PDVV RI J JLYLQJ LW D GHQVLW\ RI J FP3 7KH VDPH DPRXQW RI SXUH ZDWHU ZRXOG KDYH D PDVV RI J PDNLQJ LWV GHQVLW\ J FP3. Since the salt is dissolved in the water, the YROXPH RI WKLV VDPSOH LV WKH VDPH² FP3.

200 | Relative Density

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STEMscopedia :KDW KDSSHQV LI \RX LQFUHDVH WKH DPRXQW RI PDWWHU" ,W LV WHPSWLQJ WR WKLQN WKDW LI WKHUH LV PRUH PDWWHU then the density increases. This is not true.

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500 mL

500 mL

400

400

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300

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200

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Relative Density | 201

STEMscopedia We can compare relative density by observing how some substances behave in relation to others. Less GHQVH REMHFWV À RDW DQG PRUH GHQVH REMHFWV VLQN Relative density LV WKH FRPSDULVRQ RI WKH GHQVLW\ RI RQH PDWHULDO DV LW UHODWHV WR DQRWKHU IUHTXHQWO\ WKH FRPSDULVRQ LV WR WKH GHQVLW\ RI ZDWHU DV LQ VLQNLQJ RU À RDWLQJ ,I D ERDW À RDWV LQ ZDWHU WKLV PHDQV LW LV OHVV GHQVH WKDQ WKH ZDWHU +RZ FDQ WKLV EH WUXH LI WKH ERDW LV PDGH RI KHDY\ PHWDO" 5HPHPEHU WKDW GHQVLW\ LV QRW WKH VDPH DV ZHLJKW %RDWV DQG VKLSV KDYH ODUJH DUHDV ZKHUH DLU ¿ OOV FRPSDUWPHQWV UHGXFLQJ WKH GHQVLW\ RI WKH FUDIW DQG PDNLQJ LW PXFK OHVV GHQVH WKDQ ZDWHU 6LQFH DLU LV OHVV GHQVH WKDQ ZDWHU WKH DLU ¿ OOHG FRPSDUWPHQWV DUH OHVV GHQVH WKDQ WKH ZDWHU LQ ZKLFK WKH VKLS À RDWV ,I ZH ORRN DW D GHQVLW\ FROXPQ ZH FDQ PDNH VRPH REVHUYDWLRQV WR KHOS XV GHWHUPLQH WKH UHODWLYH GHQVLW\ RI YDULRXV OLTXLGV

7KH LPDJH VKRZV D GHQVLW\ FROXPQ PDGH RI ZDWHU RLO DQG DOFRKRO In this density column, we notice that the yellow OLTXLG RLO LV À RDWLQJ RQ WRS RI WKH UHG OLTXLG ZDWHU 6LQFH OHVV GHQVH VXEVWDQFHV À RDW RQ WRS RI PRUH GHQVH VXEVWDQFHV ZH NQRZ WKDW WKH RLO LV OHVV GHQVH than the water. We see that the blue liquid, alcohol, LV À RDWLQJ RQ WKH RLO VR LW PXVW EH OHVV GHQVH WKDQ the oil.

the comparison RI WKH GHQVLW\ RI RQH PDWHULDO DV LW UHODWHV WR DQRWKHU IUHTXHQWO\ WKH FRPSDULVRQ LV WR WKH GHQVLW\ RI ZDWHU DV LQ VLQNLQJ RU À RDWLQJ

7KHUHIRUH WKLV GHQVLW\ FROXPQ LV LQ RUGHU IURP OHDVW dense at the top to most dense on the bottom. The alcohol is the least dense, the oil is more dense, and the most dense substance is the water.

202 | Relative Density

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STEMscopedia Sophie Blanchard First Female Hot Air Balloonist 6RSKLH %ODQFKDUG LV WKRXJKW WR EH WKH ¿ UVW IHPDOH SURIHVVLRQDO EDOORRQLVW ,Q WKH V +HQU\ &DYHQGLVK GLVFRYHUHG WKH SUHVHQFH RI K\GURJHQ JDV DV LWV RZQ VXEVWDQFH DQG SHRSOH TXLFNO\ UHDOL]HG WKDW KHDWHG K\GURJHQ ZDV OHVV GHQVH WKDQ DWPRVSKHULF DLU 3HRSOH ZRQGHUHG LI WKLV QHZ VXEVWDQFH PLJKW EH XVHG WR UDLVH D KRW DLU EDOORRQ LQ À LJKW 7KH ¿ UVW IHPDOH EDOORRQLVWV EHJDQ À \LQJ VKRUWO\ DIWHU WKDW GLVFRYHU\ EXW %ODQFKDUG ZDV WKH ¿ UVW WR PDNH D FDUHHU RXW RI LW %ODQFKDUG PDGH PDQ\ ORQJ GLVWDQFH WULSV LQ KHU K\GURJHQ ¿ OOHG EDOORRQ DQG HQWHUWDLQHG DXGLHQFHV E\ FRPELQLQJ KRW DLU EDOORRQ À LJKW ZLWK ¿ UHZRUNV VKRZV %ODQFKDUG DOVR WKRXJKW KRW DLU EDOORRQV PLJKW EH XVHG LQ ZDUIDUH DSSRLQWHG D FKLHI EDOORRQLVW E\ 1DSROHRQ VKH LQYHVWLJDWHG KRZ D KRW DLU EDOORRQ À HHW PLJKW EH XVHG WR LQYDGH QHDUE\ (QJODQG ,Q VKH ZDV DSSRLQWHG WKH RI¿ FLDO EDOORRQLVW RI WKH 5HVWRUDWLRQ XQGHU /RXLV ;9,,, $ S\URWHFKQLFV GHPRQVWUDWLRQ OHG WR D KRW DLU EDOORRQ DFFLGHQW DQG KHU GHDWK LQ ZKHQ WKH K\GURJHQ LQ KHU EDOORRQ OHDNHG DQG DFFLGHQWDOO\ LJQLWHG

7KLV LOOXVWUDWLRQ VKRZV DQ DLU EDOORRQ IURP VKRUWO\ EHIRUH 6RSKLH %ODQFKDUG PDGH D FDUHHU À \LQJ D K\GURJHQ ¿ OOHG EDOORRQ © Accelerate Learning Inc. – All Rights Reserved

Relative Density | 203

STEMscopedia 'HQVLW\ LV WKH UDWLR RI D VXEVWDQFH¶V PDVV UHODWLYH WR WKH VSDFH LW RFFXSLHV 6XEVWDQFHV WKDW DUH OHVV GHQVH À RDW RQ WRS RI VXEVWDQFHV WKDW DUH PRUH GHQVH 7KH DSSUR[LPDWH GHQVLW\ RI ZDWHU LV J FP3, DQG VXEVWDQFHV WKDW DUH OHVV GHQVH WKDQ WKLV ZLOO À RDW RQ ZDWHU 6XEVWDQFHV WKDW DUH PRUH GHQVH WKDQ J FP3 ZLOO VLQN LQ ZDWHU :H FDQ GHWHUPLQH WKH UHODWLYH GHQVLW\ RI À XLGV E\ REVHUYLQJ KRZ WKH\ behave in relation to one another.

Connect It :K\ GRHV \RXU ERG\ À RDW KLJKHU LQ WKH RFHDQ WKDQ LQ WKH EDWKWXE" 'HQVLW\ LPSDFWV KRZ KLJK D À XLG RU VXEVWDQFH ZLOO À RDW 6DOW ZDWHU LV PRUH GHQVH WKDQ IUHVK ZDWHU VR \RXU ERG\ ZLOO À RDW KLJKHU LQ VDOW ZDWHU WKDQ LW ZLOO LQ IUHVK ZDWHU ZKLFK LV QRW DV GHQVH

Fresh Water

204 | Relative Density

Salt Water

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STEMscopedia 8VH WKH GHQVLW\ FROXPQ WR DQVZHU TXHVWLRQV ± 1

2

Which statement is true about the colored water?

A It is more dense than vegetable oil and dishwashing liquid.

B It is less dense than alcohol and more dense than dishwashing liquid.

C ,W LV OHVV GHQVH WKDQ GDUN FRUQ V\UXS DQG PRUH GHQVH WKDQ YHJHWDEOH RLO D It is less dense than both dishwashing liquid and alcohol. :KLFK DQVZHU FKRLFH DUUDQJHV WKH VXEVWDQFHV LQ RUGHU IURP PRVW GHQVH WR least dense?

A 9HJHWDEOH RLO DOFRKRO FRORUHG ZDWHU GLVKZDVKLQJ OLTXLG B 'DUN FRUQ V\UXS GLVKZDVKLQJ OLTXLG FRORUHG ZDWHU DOFRKRO C 'LVKZDVKLQJ OLTXLG DOFRKRO YHJHWDEOH RLO GDUN FRUQ V\UXS D 9HJHWDEOH RLO FRORUHG ZDWHU GLVKZDVKLQJ OLTXLG GDUN FRUQ V\UXS

Colored alcohol

Vegetable oil

Colored water

Dishwashing liquid

Dark corn syrup

3

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Relative Density | 205

Pure Substances and Mixtures

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207

STEMscopedia The physical properties of some pure substances make it easy to identify them. They generally look the same, with each part of the substance appearing just like the others. For instance, a bar of chocolate appears to be a pure substance.

However, it is not a pure substance, even though it appears to be.

What about a chocolate pastry like the one below?

think u o y 1. Do colate a cho pure a is pastry ce? Why n substa hy not? or w

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Pure Substances and Mixtures | 209

STEMscopedia You are familiar with the physical and chemical properties of matter—properties such as size, VKDSH WH[WXUH YROXPH À H[LELOLW\ À DPPDELOLW\ UDGLRDFWLYLW\ DQG WR[LFLW\ $ physical property is a characteristic that can be observed or measured without changing the substance. We can observe a substance’s density, for example, to help us decide what type of mixture it is.

We use tools such as rulers and triple beam balances to measure the physical properties of matter.

The chemical properties of matter can be observed in various ways by conducting a chemical reaction.

Burning a piece of paper is a chemical reaction that causes the atoms to rearrange themselves. When a chemical reaction takes place, the atoms in the matter rearrange themselves and create a new substance.

Matter is anything that has mass and takes up space or has volume. It can be a solid, liquid, or gas.

The molecular structure of matter is important in determining its physical properties. If the matter is packed together solidly, with a large number of particles in a small space, it will have high density.

Matter with fewer molecules in the same space will have lower density. If the densities of two substances are different enough, this could affect how they mix.

210 | Pure Substances and Mixtures

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STEMscopedia $ pure substance can be either an element, like copper or oxygen, or a compound, like table salt or baking soda. Pure substances are constant in their structure, composition, and properties. They are GLI¿ FXOW WR VHSDUDWH XVLQJ SK\VLFDO PHDQV Generally, any type of matter that forms crystals is a pure substance, including sugar, salt, and diamonds. For example, this means that if you take a spoonful of sugar from the top of a bag, it will KDYH H[DFWO\ WKH VDPH FRPSRVLWLRQ DV VXJDU DW WKH ERWWRP RI WKH EDJ $ VDPSOH RI FDUERQ GLR[LGH IURP air near your feet will have one carbon atom and two oxygen atoms, just like a sample of carbon dioxide taken from 20 feet up in the atmosphere.

Pure substances consist of only one kind of atom or molecule. This does not mean that they must be all the same type of atom, as an element is. Pure water, for example, made of molecules consisting of two K\GURJHQ DWRPV DQG RQH R[\JHQ DWRP LV D SXUH VXEVWDQFH $V ORQJ DV DOO RI WKH PROHFXOHV DUH LGHQWLFDO LQ FRPSRVLWLRQ WKH PDWWHU LV SXUH $Q\ HOHPHQW \RX FDQ WKLQN RI IURP JROG WR QLWURJHQ LV SXUH

This image shows two pure substances, an element and a compound. Notice that the atoms of copper are all the same, just as the molecules of salt are identical throughout the substance.

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Pure Substances and Mixtures | 211

STEMscopedia 2. Imagine g you y were looking at a substance under a powerful microscope and could see the atoms or molecules.

How could yyou tell the difference on a molecular level between a pure substance and one that is not pure?

0L[WXUHV DUH GLIIHUHQW IURP SXUH VXEVWDQFHV $ PL[WXUH LV D VXEVWDQFH PDGH ZKHQ \RX PL[ RWKHU substances together. The pure substances in the mixture are not bonded to one another, so they can be separated into their original substances easily, using tools such as a sieve or even your hand. Each LQGLYLGXDO VXEVWDQFH DOVR NHHSV LWV RZQ SURSHUWLHV )RU H[DPSOH LQ D PL[WXUH RI LURQ ¿ OLQJV DQG URFNV WKH LURQ ¿ OLQJV KDYH WKH SURSHUW\ RI PDJQHWLVP 7KH URFNV GR QRW %RWK RI WKHVH VXEVWDQFHV NHHS WKHLU properties even when mixed together.

Some of the methods you might use to separate mixtures include the following:

• Evaporation: This method works when you have a mixture where one of the substances is •

•

water. When the water is evaporated, the other substance is left behind. Salt and water are commonly separated using this method.

Filtration: 7KLV PHWKRG XVXDOO\ XVHV D PHFKDQLFDO ¿ OWHU OLNH D VLHYH WR VHSDUDWH FRPSRQHQWV RI D PL[WXUH $FWLYLWLHV OLNH SDQQLQJ IRU JROG RU ¿ OWHULQJ GLUW LQ VHDUFK RI VPDOO ERQHV ZRXOG XVH ¿ OWUDWLRQ 2Q D VPDOOHU OHYHO ¿ OWUDWLRQ FDQ EH XVHG WR UHPRYH LPSXULWLHV IURP ZDWHU DLU RU other substances.

Chromatography: This method will separate mixtures with components that move through a medium at different rates. It works well for separating things that have several colors, such as the marks made by black markers.

212 | Pure Substances and Mixtures

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STEMscopedia separate the salad into piles of each ingredient because the molecules of each ingredient are clumped together, making them easy to separate.

Mixtures also can have varying ratios of the pure substances that compose them. For example, the salad may only have a few tomatoes but lots of lettuce. Therefore, different bites of the same salad might not contain identical amounts of each vegetable. $ PL[WXUH FDQ EH RQH RI WZR NLQGV KRPRJHQHRXV RU KHWHURJHQHRXV 7KH PDLQ GLIIHUHQFH EHWZHHQ WKH two types is the distribution of the particles. Let’s take a closer look.

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Pure Substances and Mixtures | 213

STEMscopedia $ homogeneous mixture is a type of mixture that consists of more than one pure substance and has its ingredients uniformly mixed. This means that although there are molecules of more than one substance in the mixture, the molecules of those substances are spread evenly throughout the mixture.

This also means that the mixture has the same physical appearance throughout.

Homogeneous Mixture

Heterogeneous Mixture

Lemonade

Chocolate chip cookie

Homogeneous mixtures can be hard to separate because the molecules of each pure substance are spread evenly throughout the mixture, although it is possible to do so using physical means. You can’t separate the molecules from each other easily.

For example, when we mix sugar and water, the water molecules are evenly spread between the sugar PROHFXOHV 7R RXU H\H WKH VXJDU LV IXOO\ GLVVROYHG LQ WKH ZDWHU 7KHUH LV QRW RQH VSHFL¿ F SODFH ZLWKLQ WKH mixture where we can see more sugar than water.

Homogeneous mixtures are all around us. Rain, steel, chocolate, orange juice, and soda without ice are examples of homogeneous mixtures.

214 | Pure Substances and Mixtures

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STEMscopedia

+ Water

= Sand

+ Water

= Sugar

You may have heard of a solution, which is a special kind of homogeneous mixture. Solutions have a uniform composition formed when one solid substance, called a solute, is added to a liquid substance, called a solvent, creating a homogeneous mixture whose parts we cannot see with our naked eye.

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Pure Substances and Mixtures | 215

STEMscopedia Salt Water or Sugar Water Water particle

Salt or sugar particle

$W OHDVW RQH RI WKH VXEVWDQFHV LQ D VROXWLRQ ZLOO KDYH WKH DELOLW\ WR GLVVROYH HDVLO\ This physical property is known as solubility.

216 | Pure Substances and Mixtures

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STEMscopedia sugar molecules to water molecules remains the same throughout the sugar water, even if it is mixed again with other substances. The table below compares homogeneous mixtures and solutions.

Mixtures Substances are physically combined; no new substance is formed; can be separated Homogeneous Mixture

Solution (a special kind of homogeneous mixture where one substance is dissolved in another)

Molecular Structure

Molecules are evenly distributed within the substance; can be elements or compounds

Even distribution of molecules at the microscopic level

How to Separate

Settling, straining with a VLHYH ¿ OWHU SDSHU PDJQHWV ¿ QJHUV WZHH]HUV

Evaporation

Physical Properties Affecting the Mixture’s Ability to Separate

Magnetism, particle size (can be large or small), state of matter, density

Small particle sizes, melting or boiling point, always a solid dissolved in a liquid

Examples

Homogenized milk, rain, coffee, blood, gasoline

Salt water, sugar and water, gas in the air, metal alloys such as brass

3. Nam homoge e a mixture neous a solut that is also io how th n. Discuss e are dis molecules trib your e uted in xample .

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Pure Substances and Mixtures | 217

STEMscopedia 7KH RWKHU W\SH RI PL[WXUH LV D KHWHURJHQHRXV PL[WXUH $ heterogeneous mixture is a mixture which has its ingredients combined, but they are not uniformly mixed. Generally, if a mixture is made of substances with different densities, the molecules in each substance will not mix evenly.

/HW¶V ¿ UVW ORRN DW ZDWHU DQG VDQG 7KH VDQG SDUWLFOHV FROOHFW RQ WKH ERWWRP RI D FRQWDLQHU ZKHQ PL[HG with water, and our eyes can see the individual sand particles, which are mixed with the water but not evenly. If we used a pipette to take a sample of the sand and water mixture from the top of the container, we would probably see more water molecules than sand. However, if we took a sample from the bottom of the container, we would get more sand molecules and fewer water molecules in that sample.

Trail mix and chicken soup are examples of other heterogeneous mixtures. So are pizza and RDWPHDO UDLVLQ FRRNLHV DV ZHOO DV LURQ ¿ OLQJV PL[HG ZLWK URFNV $ PL[WXUH RI URFNV DQG ZDWHU LV DOVR heterogeneous since the substances are not evenly distributed throughout the mixture.

218 | Pure Substances and Mixtures

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STEMscopedia

2LO DQG ZDWHU IRUP D KHWHURJHQHRXV PL[WXUH 7KH GHQVLW\ RI WKH RLO ZKLFK LV PXFK OHVV WKDQ water, causes the two substances to mix unevenly.

4. Wh prope at r hetero ties do substa geneous nces have?

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Pure Substances and Mixtures | 219

STEMscopedia Krithika Ramchander Massachusetts Institute of Technology In her work with the Massachusetts Institute of Technology, Krithika Ramchander is developing WHFKQRORJ\ IRU D ORZ FRVW ZDWHU ¿ OWHU WKDW XVHV SODQW WLVVXH WR UHPRYH LPSXULWLHV ,W ZRXOG EH XVHG LQ UXUDO FRPPXQLWLHV LQ ,QGLD WKDW KDYH OLPLWHG DFFHVV WR ZDWHU ¿ OWUDWLRQ WHFKQRORJ\ 6KH DQG KHU FROOHDJXH Dr. Rohit Karnik GLVFRYHUHG WKDW RQH NLQG RI ZRRG VDSZRRG ¿ OWHUV XS WR RI E. colii from up to 4 liters of drinking water per day, which is the amount of drinking water needed by one person each day.

E. colii is a bacterium that normally lives inside humans; however, some types can make humans very sick if ingested through food or water.

Many rural communities in India do not have reliable access to clean drinking water.

Krithika Ramchander, along with her colleague Dr. Rohit Karnik, is developing technology to change that.

220 | Pure Substances and Mixtures

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STEMscopedia 3XUH VXEVWDQFHV FDQ EH HLWKHU HOHPHQWV RU FRPSRXQGV $ SXUH VXEVWDQFH KDV LGHQWLFDO DWRPV RU molecules throughout the substance. There are two main types of mixtures. Homogeneous mixtures have more than one pure substance, and the particles of each substance are evenly distributed WKURXJKRXW WKH PL[WXUH 2QH VSHFLDO W\SH RI KRPRJHQHRXV VXEVWDQFH LV D VROXWLRQ ZKHUH RQH VXEVWDQFH (the solute) is dissolved into another (the solvent). Heterogeneous mixtures also contain more than one pure substance, but the particles of each pure substance are not evenly distributed throughout.

Connect It Are pastries pure substances?

1R 3DVWULHV DUH PDGH RI VHYHUDO SXUH VXEVWDQFHV OLNH EDNLQJ VRGD DQG À RXU &KRFRODWH LV DOVR QRW D pure substance, because it is made of cocoa, oils, and sugar, which are pure substances themselves. &KRFRODWH DQG SDVWULHV DUH ERWK PL[WXUHV 'HSHQGLQJ RQ KRZ WKH\ DUH PL[HG DQG WKH LQJUHGLHQWV composing them, they can be either homogeneous or heterogeneous mixtures.

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Pure Substances and Mixtures | 221

STEMscopedia Summarize It 1

Imagine you observe a heterogeneous mixture that can be easily separated by using a magnet.

Which statement about its properties is most likely correct?

A 2QH VXEVWDQFH LV PDJQHWLF DQG WKH RWKHU LV QRW B The particles of both substances composing the mixture are evenly distributed.

C The substance with the lowest density would be mostly at the bottom.

D The mixture is a type of solution.

2

What is the main difference between a solution and a heterogeneous mixture?

A $ KHWHURJHQHRXV PL[WXUH KDV SDUWLFOHV WKDW DUH HYHQO\ GLVWULEXWHG B $ VROXWLRQ FDQQRW EH D PL[WXUH DV ZHOO D VXEVWDQFH PXVW EH RQH RU WKH RWKHU C $ KHWHURJHQHRXV PL[WXUH LV FUHDWHG ZKHQ D VROLG LV GLVVROYHG LQ D OLTXLG DQG D VROXWLRQ KDV unevenly distributed particles.

D $ VROXWLRQ LV FUHDWHG ZKHQ D VROLG LV GLVVROYHG LQ D OLTXLG DQG D KHWHURJHQHRXV PL[WXUH KDV unevenly distributed particles.

3

If you add ice to a glass of soda, which of the following statements is true about the drink?

A The soda and ice mixture becomes a solution because the soda dissolves into the ice.

B The soda and ice mixture is homogeneous because the ice will make all of the soda the same temperature.

C The soda and ice mixture is a heterogeneous mixture because the ice and soda are not evenly mixed and can be easily separated.

D The soda and ice mixture is a heterogeneous mixture because the ice and soda are evenly mixed and can be separated.

4

$ VWXGHQW FRQGXFWV DQ LQYHVWLJDWLRQ ZKHUH WKH\ GURS DQ LURQ QDLO LQWR D EHDNHU FRQWDLQLQJ VDOW DQG hydrogen peroxide. The substances combine and undergo a chemical change, forming rust. Which of the following statements best describes the rust and the nail together?

A The nail is a heterogeneous mixture, and the rust is a homogeneous mixture since it was created as a new substance after a chemical change.

B The rust is a solution since it will dissolve in water, and the iron nail is a homogeneous mixture made of one type of atom.

C The rust and the nail are the same throughout, so it is a homogeneous mixture.

D The substances composing rust and the nail are not the same throughout, so they form a heterogeneous mixture.

5

&RPSDUH WKH SURSHUWLHV RI D SXUH VXEVWDQFH DQG D VROXWLRQ

222 | Pure Substances and Mixtures

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Properties of Acids and Bases

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223

STEMscopedia Have you ever wondered what makes salsa taste the way it does? Why do people prefer some varieties of salsa over others? And what properties does the salsa have that make it taste good with certain foods?

It has to do with a property called pH. This property affects not only how foods like salsa taste but also their safety when canned and sent to the grocery store. Often, salsa recipes call for the addition of lime or lemon juice before the product is sealed and delivered. But why would tomatoes, an acidic substance, need to have more acid added to them?

s are e o t a m 1. If to hy is lime w acidic, ed to salsa dd juuice a canning? before

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Properties of Acids and Bases | 225

STEMscopedia When a solution is dissolved in water, it sometimes will release extra positive hydrogen ions, or it may receive extra hydrogen ions. Scientists call this the potential of hydrogen or power of hydrogen and shorten that expression to the term pH. A substance’s pH is a measure of its acidity or alkalinity when dissolved into an aqueous solution.

The pH of a solution is ranked on the pH scale. The pH scale ranges from 0 to 14 and measures the concentration of hydrogen ions that the substance has in a solution. This property of a solution is important in many areas like medicine, agriculture, and cooking.

A substance’s pH is measured on a scale ranging from 0 to 14.

226 | Properties of Acids and Bases

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STEMscopedia The middle number on the scale, 7, is considered neutral. A neutral solution has a pH of 7. Water is a relatively neutral substance in that it is not acidic or basic but ranks in the middle of those properties.

Other substances are ranked on the pH scale as their concentrations of hydrogen ions are compared to those in water. A change of one unit on the pH scale represents a tenfold change in the concentration of hydrogen ions in a particular solution. A substance with a pH lower than 7 is considered acidic, and one with a pH higher than 7 is considered alkaline or basic.

Scientists use the pH scale to quantify the measure of hydrogen ions in a substance. The more hydrogen ions present, the lower the pH, and substances with a higher pH have fewer hydrogen ions present.

We use acidic and basic substances in everyday life.

This image of the pH scale shows the pH values of common household substances. Acids have a pH lower than water, and alkaline (basic) substances have a pH higher than water.

e the r a t a 2. Wh ristics of a te charac l solution on neutra H scale? the p

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Properties of Acids and Bases | 227

STEMscopedia An acid is a compound that produces hydrogen ions in solution, donates hydrogen ions, or is an electron-pair acceptor. Solutions that are acidic make hydrogen ions when dissolved in water. For example, hydrochloric acid, or HCl, breaks up or dissociates in water, creating positively charged hydrogen ions. Acidic substances donate hydrogen ions to other compounds when dissolved into a solution. The stronger an acid is, the more easily it dissociates in water, producing hydrogen ions.

Acids taste sour and will neutralize basic substances when combined with them. They react with metals to produce hydrogen gas, which is extremely volatile. In addition, acids will turn blue litmus paper red. $FLGV IHHO ZDWHU\ RU VTXHDN\ EHWZHHQ RXU ¿ QJHUV Acids are recognizable for their squeaky feel. Many foods are acidic, such as citrus fruits like oranges, lemons and limes, apples, and tomato products. Humans enjoy the taste of acidic foods, so they are used widely in food preparation. Some everyday examples of acids include battery acid, vinegar, lemon juice, coffee, and stomach acid.

Apples, apple cider vinegar, and regular vinegar are examples of acidic foods that have a low pH and a sour taste.

you n a c w 3. Ho ish an u disting from a food acidic one? basic

228 | Properties of Acids and Bases

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STEMscopedia A base is a compound that releases hydroxide ions in solution. It accepts hydrogen ions or donates an electron pair when dissolved in water. Bases have a pH that is higher than water, and they will neutralize acids when combined with them. They turn red litmus paper blue and feel slippery or slimy to the touch.

Sometimes they are referred to as alkaline substances.

Almost all of the cleaning products we use around the house are basic, including baking soda, bleach, and dishwashing soap. This is because of the presence of metal pipes in older homes. Since acids break down metal pipes, scientists needed a solution with different properties that could be poured down drains without corroding pipes. They began using basic substances in formulas for cleaning chemicals, and we have continued to use them because of their effectiveness. Substances like ammonia and drain cleaner are basic.

We also use bases to cleanse our bodies. Strong bases react with the fatty acids and oils that naturally occur on the surface of skin. This produces a soap-like solution that dissolves oils and keeps our skin clean. In addition, we use acid-neutralizing tablets to raise the pH of the acid in our stomachs.

These substances have a pH higher than 7. Another way to describe a basic substance is to say that it is alkaline.

Almost all cleaners we use at home are bases, with a pH higher than water and a greasy or slippery feel.

y is it e h W .

4 mak o t t n a import ld cleaners o househ are basic that cidic? a f o d instea

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Properties of Acids and Bases | 229

STEMscopedia An acid and a base react in an acid-base reaction, which is also known as a neutralization reaction. The result of this reaction is the production of water and the formation of a salt. The salt may be acidic, basic, or neutral in terms of its pH level. The nature of acidic or basic salts depends on the acid or base that the salt evolved from in the reaction. The most well-known salt is sodium chloride, which is what we use for table salt. It is formed when the strong base sodium hydroxide and strong acid hydrochloric acid combine. Other salts you may have heard of include Epsom salts often used in bath salts, ammonium nitrate used in fertilizer, and baking soda used in cooking. The pH of a salt solution depends on the strengths of the acids and bases that combine.

230 | Properties of Acids and Bases

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STEMscopedia Because of the properties of acids and bases, they affect the well-being of various plants and animals.

Many organisms are sensitive to even small changes in pH within their environments. The pH level in an ocean affects how well corals can form calcium for their skeletons, and reabsorption of CO2 in the atmosphere can affect the acidity of the oceans. Large changes in the pH of blood in the human body can make us very sick.

Soil pH is important in the agriculture industry. Adjustments sometimes need to be made in soil so that other varieties of crops will thrive. In addition, using soil additives such as lime and certain fertilizer varieties can change the color of some plants, like this hydrangea. The variations in color can be created E\ FKDQJLQJ WKH S+ RI WKH VRLO $FLGLF VRLO UHVXOWV LQ EOXH À RZHUV OLNH WKRVH DW WKH ULJKW RI WKLV LPDJH ZKLOH PRUH EDVLF VRLOV UHVXOW LQ SLQN À RZHUV OLNH WKRVH DW WKH OHIW RI WKH LPDJH EHORZ

0RVW YDULHWLHV RI ¿ VK SUHIHU D S+ FORVH WR %HFDXVH RI WKLV WKH DTXDFXOWXUH LQGXVWU\ PDNHV DW KRPH aquarium test kits that can be used by hobbyists to be sure that the properties of their aquarium water DUH LGHDO IRU WKH VSHFLHV RI ¿ VK WKH\ KDYH

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Properties of Acids and Bases | 231

STEMscopedia

African cichlids like these prefer a pH between 7.4 and 9.0. Some of the corals in the image were added to maintain a higher-than-neutral pH in this home aquarium.

Many industries also use this principle. Wastewater treatment uses basic substances because bases prevent the growth of bacteria. This is also why basic substances like chlorine and bleach are used in pool and spa care. Bases prevent bacteria from colonizing and growing, which could negatively affect the health of people swimming in untreated water.

Another industry that uses this knowledge is the food and beverage industry. Acidic substances taste good to humans. The food and beverage industry manipulates pH in some substances or chooses food combinations based on pH in order to appease customers and provide a product consumers like.

is pH w o H .

5 r ant fo t r o p im rvival u s e h t nisms? a g r o of

232 | Properties of Acids and Bases

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STEMscopedia Mary K. Firestone University of California, Berkeley Mary K. Firestone works as a soil microbial ecologist who investigates how microorganisms in soil interact with their environments. She also works to understand how soil microbes contribute to the carbon and nitrogen cycles of plants. She and her team members work to run experiments on how microbes in soil can contribute to and change climate and how they can make soil more sustainable and XVH ODQG LQ EHWWHU PRUH HI¿ FLHQW ZD\V She has also worked with new ecologists to help develop their careers while studying at the University of California, Berkeley.

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Properties of Acids and Bases | 233

STEMscopedia A substance’s pH is a measure of its acidity or alkalinity when dissolved into an aqueous solution. The pH of a solution is ranked on the pH scale, which measures the concentration of hydrogen ions that the substance has in a solution.

Acids are recognizable for their sour taste and squeaky feel. Acidic substances donate hydrogen ions to other compounds when dissolved into a solution and have a pH of less than 7. A base is a compound that releases hydroxide ions in solution. It accepts hydrogen ions or donates an electron pair when dissolved in water. Bases have a pH that is higher than 7, higher than pure water, and they will neutralize acids when combined with them. They turn red litmus paper blue, taste bitter, and feel slippery or slimy to the touch.

Connect It Why is lime juice added to containers of salsa before they are sealed?

Salsa contains large amounts of tomatoes, which have an acidic pH. Lime or lemon juice is added to salsa to be sure the pH remains acidic enough to prevent the growth of certain bacteria and keep the product safe for human consumption.

234 | Properties of Acids and Bases

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STEMscopedia Acids and bases can also be described in terms of ions. The simplest way to understand acids and bases is to review the equation for water. Natural water dissociates, forming the hydronium and hydroxyl ions.

This can be represented by the equation below.

2H2O ĺ H3O+ + OHí The molecule that makes a substance acidic is the H3O+ molecule, called hydronium. This molecule is sometimes referred to as H+ in shorthand; but this practice can be confusing because sometimes what is being represented is a hydrogen ion and not a hydronium ion. The other ion is a hydroxyl ion, whose chemical formula is OH-. Because water has an equal number of hydronium and hydroxyl ions, water is considered neutral.

When acids dissociate in water, more hydronium than hydroxyl ions are created, making the solution acidic. Let’s review hydrochloric acid. The chemical equation for the dissociation of HCl is written below.

HCl + H2O ĺ H3O+ + Clí The hydrogen from the hydrochloric acid joins with the water molecule to make a hydronium ion and a chloride ion.

When bases dissociate in water, more hydroxyl ions than hydronium ions are created, making the solution basic. Let’s review sodium hydroxide, which is a common base. The chemical equation for the dissociation of NaOH is written below.

NaOH ĺ OHí + Na+ The sodium hydroxide breaks apart into a hydroxyl ion and a sodium ion.

The more hydronium ions that a substance dissociates into, the more acidic that substance is on the pH scale. The more hydroxyl ions that a substance dissociates into, the more basic the substance is.

The pH scale is a logarithmic scale that measures the hydronium ion concentration in a substance.

The hydronium ion concentration and pH are related inversely, meaning that the presence of more hydronium ions in a substance indicates a lower pH. Hydroxyl ions are directly related to pH, meaning that the presence of more hydroxyl ions in a substance indicates a higher pH. Having more hydroxyl ions means having a lower concentration of hydronium ions, and this indicates a substance with a higher pH. Some common substances and their pH values are shown below.

1M

pH

0

[H + ] 1

ric

t as

G

1

e

ic

I C H

2

ju

O

n ra

ge

ju

ic

e

e in W

C

4

5

3

er er at w d at w e o k r a il lo M Pu B Se

e ffe

o

6

7

8

9

10

s ia nt ge on h r m eac e t m l e A B D

1M

11

14

12

13

H

aO

N

10 -1 10 -2 10 -3 10 -4 10 -5 10 -6 10 -7 10 -8 10 -9 10 -10 10 -11 10 -12 10 -13 10 -14

[OH - ] 10 -14 10 -13 10 -12 10 -11 10 -10 10 -9 10 -8 10 -7 10 -6 10 -5 10 -4 10 -3 10 -2 10 -1

More acidic

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Neutral

1

More basic

Properties of Acids and Bases | 235

STEMscopedia Summarize It 1

What properties of a base help scientists identify it?

A Relative pH lower than water and a slippery texture B Relative pH higher than water and a sour taste C Relative pH higher than water and a slippery texture D Relative pH lower than water and a sour taste

2

A substance has a sour taste. Which of the following properties would NOT be present in the substance?

A Makes hydrogen ions when dissolved in water B Squeaky feel C Relative pH lower than water D Makes hydroxide ions when dissolved in water

3

How does pH impact living things?

A pH ensures that organisms can get enough acid from the environment.

B Improper pH can interfere with life processes and possibly kill an organism.

C An overall basic (alkaline) pH helps humans digest foods in their stomachs.

D Improper pH does not impact living things except to cause their color to change.

4

A student was investigating the properties of various liquids and made a data table.

Substance

pH

Properties

A

9

Slippery feel

B

8

Bitter taste

C

5

Sour taste

D

7

Neutral taste

Which substance is an acid?

A Substance A B Substance B C Substance C D Substance D 5

What is the effect of adding a basic substance such as a stomach acid reducer to an acidic substance?

A It raises the pH of the acid and brings it closer to neutral.

B It lowers the pH of the acid and brings it away from neutral.

C It brings the pH of the solution to 7.

D It neutralizes the solution.

6

Describe the properties of acids and bases.

236 | Properties of Acids and Bases

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Photosynthesis and Cellular Respiration

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237

STEMscopedia Plants are living organisms. Like all living things, plants need energy to survive. How do plants get energy? Do you think plants are able to breathe? If plants grow and reproduce, do they also eat?

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Photosynthesis and Cellular Respiration | 239

STEMscopedia Matter is anything that has mass and takes up space. Matter can’t be created or destroyed, just rearranged. Mass is a measure of the amount of matter in an object or substance. In a chemical reaction, the reactants are what’s required for the reaction to occur. You can think of reactants as ingredients in a recipe. The products of a chemical reaction are what is produced because of the reaction. Reactants are on the left side of a chemical equation, and products are on the right side. In the diagram below, you can see the atoms and molecules involved in photosynthesis and the chemical equation at the bottom.

Photosynthesis Carbon dioxide (gas)

Water

(liquid)

6CO2 + 6H2O

240 | Photosynthesis and Cellular Respiration

Sunlight

Oxygen (gas)

Glucose (solid)

6O2 + C6H12O6

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STEMscopedia atter m e c 1. Sin created or s be can’t ed and mas e y destro asure of th e , is a m t of matter amoun s this say doe what e total mass th s about actant e r e of th ducts in a ro and p l reaction? a chemic

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Photosynthesis and Cellular Respiration | 241

STEMscopedia In the photosynthesis reaction, radiant energy from the Sun is used to rearrange 6 carbon atoms, 12 hydrogen atoms, and 18 oxygen atoms in the reactants into a different arrangement in the products.

Mass is conserved, because the number of atoms of each element in the reactants (carbon, hydrogen, and oxygen) is the same as the number of atoms of each element in the products (carbon, hydrogen, and oxygen). However, the arrangement of the atoms is different on each side. Atoms in the reactants GRQ¶W GLVDSSHDU WKH\ MXVW FKDQJH FRQ¿ JXUDWLRQ

6CO2 + 6H2O

C6H12O6 + 6O2

Green plants are autotrophs—they make their own food through the process of photosynthesis. Green plants contain the green pigment chlorophyll inside organelles called chloroplasts. Chlorophyll’s job is to absorb sunlight. The energy in the absorbed sunlight is used to convert carbon dioxide (exhaled by animals and humans into the atmosphere) and water (taken from air and soil) into glucose and oxygen. Glucose is a carbon-based molecule. The energy from light is stored as chemical energy in the bonds of the glucose molecules. This is an example of the law of conservation of energy. The oxygen that is produced during photosynthesis is released into the atmosphere, where it can be inhaled by animals and humans. Plants use glucose, as well as nutrients from soil, to make plant parts like new leaves.

d als an im n A 2. s are ing n a m u n h s, mea eir h p o r t hetero n’t make th o they d food through do own is. How s s e h t n y n photos and huma animals the glucose ? obtain d to survive ee they n

242 | Photosynthesis and Cellular Respiration

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STEMscopedia All organisms need energy so their cells can function. This energy comes from the process off cellular respiration. During cellular respiration, the glucose generated from photosynthesis—in the presence of oxygen—is gradually broken down to carbon dioxide and water. During the process, energy known as ATP (adenosine triphosphate) is produced. ATP is the energy that cells use to perform their functions.

The carbon dioxide product of cellular respiration is exhaled, and the water can be used for other reactions or sent out of the body via the lungs or kidneys.

Without the oxygen that cellular respiration brings into the cells, organisms would not be able to run any of the processes they need to survive. These processes include digesting food, maintaining pH levels, ¿ OWHULQJ ZDVWH IURP WKH NLGQH\V SXPSLQJ EORRG DQG QXWULHQWV WKURXJK WKH ERG\ DQG PDQ\ RWKHUV

s nt cell la p o 3. D erform p o t need espiration? r cellular

Complementary Processes The processes of photosynthesis and cellular respiration are intertwined. They are complementary processes that allow organisms to obtain substances needed for life. Carbon dioxide, water, glucose, and oxygen are involved in both processes but in different ways. The products of photosynthesis (glucose and oxygen) become the reactants of cellular respiration. The products of cellular respiration (carbon dioxide and water) become the reactants during photosynthesis. Also, in both processes, energy is involved and conserved. Light energy is transformed into chemical energy, which is stored in glucose during photosynthesis, and that energy is released when glucose is broken down during cellular respiration.

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Photosynthesis and Cellular Respiration | 243

STEMscopedia

t does a h W 4. ement d t a t s the sis an e h t n y “Photos respiration cellular pleementary m are co ses” mean? proces

244 | Photosynthesis and Cellular Respiration

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STEMscopedia Hans Krebs Biochemist Hans Krebs was a biochemist who received the Nobel Prize in Physiology or Medicine in 1953 for his discovery of the Krebs cycle, also known as the tricarboxylic acid cycle or the citric acid cycle. The Krebs cycle is a part of the process of cellular respiration. His work helped provide a deeper understanding of cellular respiration.

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Photosynthesis and Cellular Respiration | 245

STEMscopedia Photosynthesis and cellular respiration are complementary processes that allow organisms to obtain substances necessary for life. During photosynthesis, the plant pigment chlorophyll absorbs light from the Sun, and the energy is used to convert carbon dioxide and water (the reactants) into glucose and oxygen (the products). The energy from light is stored in the bonds of the glucose molecules as chemical energy. Cellular respiration is the process where the bonds of the glucose molecule are broken down to release energy known as ATP (adenosine triphosphate). ATP is the energy that cells use to perform their functions. The reactants of cellular respiration are glucose and oxygen, and the products are carbon dioxide, water, and ATP.

Connect It So, do photosynthesis and cellular respiration follow the law of conservation of mass?

Another way to ask the question is this: Is mass conserved during the processes of photosynthesis and cellular respiration? Yes, both processes follow the law of conservation of mass. In other words, the mass of any one element at the beginning of a chemical reaction will equal the mass of that element at the end of the reaction. In the chemical reactions of photosynthesis and cellular respiration, the number of atoms of each element in the reactants is equal to the number of atoms of each element in the products. This is the law of conservation of mass.

Advanced Topics Cellular respiration is the process by which cells convert chemical energy stored in compounds, such as sugar, into useful energy. This energy allows organisms to perform cellular functions. Cellular respiration can happen in two ways: aerobic or anaerobic. Aerobic respiration happens in the presence of oxygen, while anaerobic respiration happens in the absence of oxygen.

Anaerobic

Memb brane

Aerobic

In mitochondria

2 ATP SFTQJSBUJPO UBLFT QMBDF 6 carbon compound Glucose 4 ADP JO UIF DZUPTPM Loss of hydrogen (oxidation) 4 ATP QSPEVDFT MFTT +O Pyruvate 3 carbon compound CO + H O acid "51 BOE Homolactic SFTVMUT JO Yeast fermentation 2 ATP fermentation 34 ADP 34 ATP GFSNFOUBUJPO Lactic Alcohol + acid CO BMDPIPM PS MBDUJD BDJE Mitochondrion Cytosol 2

2

2

2

246 | Photosynthesis and Cellular Respiration

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STEMscopedia Which gas do animals add to the atmosphere when they breathe?

A Nitrogen B Oxygen C Carbon dioxide D Hydrogen

2

Animals and humans get the energy they need for life functions such as growth, repair, and reproduction from which process?

A Breaking down glucose molecules from photosynthesis B Absorbing water from the environment C Moving numerous molecules across membranes D Eliminating waste products

3

What components are consumed in the process of photosynthesis?

A Oxygen and carbon dioxide B Glucose and water C Water and carbon dioxide D Oxygen and glucose

4

Which description best summarizes photosynthesis?

A A chemical reaction involving nitrogen and other atmospheric gases B A process by which plants produce sugar using the energy of sunlight C An adaptation of plants that allows them to add nutrients to the soil D An exchange of gases between animals and the air or water of their habitat

5

Which of the following best summarizes the process of cellular respiration in plants and animals?

A Carbon-based molecules + oxygen ĺ Carbon dioxide + water B Oxygen + carbon dioxide ĺ Carbon-based molecules + water C Water + carbon dioxide ĺ Oxygen + carbon-based molecules D Carbon dioxide + carbon-based molecules ĺ Oxygen + water

6

The diagram shown below illustrates one way carbon can be transferred.

Ca rb o

1

n

Plants A B C D

Atmosphere

Animals

Evaporation Cellular respiration Transpiration Photosynthesis

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Photosynthesis and Cellular Respiration | 247

The Carbon Cycle

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249

STEMscopedia Matter is anything that has mass and takes up space. Carbon is matter contained in both living and nonliving things. Carbon is the basis of life on Earth. It’s in our bodies, our food, the air, the ocean, rocks, and other places. Carbon is cycled through Earth over and over again. How do you think this is possible?

F

s isn’t ed s a m y 1. If destro ion, r o d create mical react is th he in a c you think to do what elation r in means rbon cycle? t a the ca hink of wh ou t n Can y phenomeno this d? is calle

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The Carbon Cycle | 251

STEMscopedia Carbon cycles through Earth’s systems in many ways, like a big recycling process. Carbon atoms continually move from the atmosphere to Earth and back to the atmosphere. Earth is a closed system, meaning matter doesn’t enter or leave. Because of this, carbon (along with other life essentials such as nitrogen, water, and oxygen) is simply recycled. For example, coal is formed from plant remains buried deep within Earth’s crust. It is mostly composed of carbon. When coal is burned for energy (a chemical reaction), its carbon atoms become carbon dioxide that is released into the atmosphere.

Cellular Respiration, Photosynthesis, and the Carbon Cycle

Systems on Earth are healthiest when their various components are balanced. Carbon is an essential element for life on Earth and is found in all four major spheres (atmosphere, biosphere, hydrosphere, and lithosphere). It moves between living and nonliving things on Earth. These movements make up the carbon cycle. When carbon is found in living things, it is called organic carbon. When it’s found in nonliving things, it is known as inorganic carbon.

In the atmosphere, carbon exists mostly as carbon dioxide, which is considered inorganic. Carbon dioxide is a very important gas in our environment. It traps heat in the atmosphere, helping to keep Earth warm enough to support life.

In the biosphere, plants can store large amounts of carbon dioxide in their leaves, stems, and roots.

Carbon dioxide is a reactant in the process of photosynthesis, which means this process removes carbon dioxide from the atmosphere. On the other hand, carbon dioxide is a product of cellular

252 | The Carbon Cycle

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STEMscopedia respiration, which means this process releases carbon dioxide into the atmosphere when we exhale.

Recall that during photosynthesis, in the presence of energy from sunlight, plants convert carbon dioxide and water into glucose and oxygen. The Sun’s energy is stored in the chemical bonds of the glucose molecules. When organisms consume carbohydrates (glucose) produced by plants, the chemical bonds are broken, and the molecules are rearranged. The Sun’s energy that is held within the chemical bonds of the molecules is transferred to adenosine triphosphate (ATP) and used to fuel cellular activities.

This is the process of cellular respiration. Can you see that energy is recycled between photosynthesis and cellular respiration? This is an example of the law of conservation of energy.

s re, doe u t a n 2. In respiration cellular ce in both la take p and animal plant f it does, I cells? occur at can it time as me the sa ynthesis? photos

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The Carbon Cycle | 253

STEMscopedia

Along with cellular respiration and photosynthesis, other processes are involved in the exchange of carbon within the carbon cycle. The bodies of organisms are primarily composed of carbon. Carbon in biomass is returned to the environment through decomposition. That is, when an organism dies, worms, bacteria, fungi, and other decomposers break it down into its component elements. Carbon enters the soil. In the United States, about 50% of the total carbon stored in forests is in the soil.

As parts of plants and other organisms decay, carbon dioxide is released back into the atmosphere.

Photosynthesis, respiration, and decomposition happen in the oceans as well as on land. In the oceans, FDUERQ F\FOHV EHWZHHQ WKH VXUIDFH RFHDQ WKH GHHS RFHDQ DQG WKH VHDÀ RRU As organisms decompose, layer upon layer of sediment forms. Heat and pressure within Earth’s crust cause the formation of fossil fuels: coal, petroleum, and natural gas. This process takes a very long time.

Fossil fuels store carbon from plants and animals that lived millions of years ago. It’s said that most of the fossil fuels in existence today come from 200–400 million years ago, during the Carboniferous Period.

Humans burn fossil fuels to generate energy that runs machines, heats buildings, and powers vehicles, among other things. While all these things are necessary, burning fossil fuels releases large amounts of carbon dioxide into the atmosphere.

ussed c is d ’ve 3. We portance the im n dioxide. bo of car might be What uence of eq a cons ing large releas of carbon ts amoun into the dioxide re due to he atmosp fossil fuels? g burnin 254 | The Carbon Cycle

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STEMscopedia Young trees that are growing quickly take in and store carbon at a fast rate. They increase biomass through photosynthesis, and they take in more carbon dioxide than they release through cellular respiration. As trees age, this rate slows. Mature forests may have a balance between carbon uptake and release, making them carbon neutral. In mature forest ecosystems, large amounts of carbon are stored in the soil and in biomass. )LUH UHOHDVHV FDUERQ GLR[LGH LQWR WKH DWPRVSKHUH 'XULQJ D IRUHVW ¿ UH RUJDQLF PDWWHU LV FRQVXPHG DQG FDUERQ GLR[LGH LV UHOHDVHG 3ODQWV DQG WUHHV WKDW DUHQ¶W FRQVXPHG E\ WKH ¿ UH FDQ GLH DQG GHFRPSRVH quickly, also releasing carbon dioxide.

Recent research has shown that while volcanoes release large amounts of carbon dioxide when they erupt, they also can remove carbon through the process of weathering. Chemical weathering of volcanic rock releases calcium, magnesium, or sodium ions. These elements form minerals that can lock up carbon dioxide. Additionally, weathered volcanic rocks can wind up in the ocean and help to trap carbon dioxide.

The “Human Factor” and the Carbon Cycle As previously stated, humans contribute to the carbon cycle by burning fossil fuels and other forms of biomass, such as wood. Biomass also burns through natural processes. For example, a bolt of lightning FDQ VSDUN D IRUHVW ¿ UH +RZHYHU RYHU WKH SDVW IHZ FHQWXULHV KXPDQV KDYH UHOHDVHG ODUJH TXDQWLWLHV of carbon into the atmosphere—more than can be absorbed through photosynthesis and other natural processes. Scientists have evidence that this excess carbon dioxide is trapping heat at Earth’s surface, leading to global climate change. The ocean absorbs large amounts of excess carbon dioxide released through the burning of fossil fuels and other processes. In the ocean, carbon dioxide reacts with seawater to form carbonic acid.

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The Carbon Cycle | 255

STEMscopedia removing a wide area of trees for agricultural or building purposes. While forests take in a large amount of carbon dioxide due to photosynthesis, they also release large amounts of carbon when trees are cut GRZQ DQG ODQG LV FRQYHUWHG IRU RWKHU XVHV :KHQ WUHHV DUH FOHDUHG RU EXUQHG VLJQL¿ FDQW DPRXQWV RI stored carbon are released into the atmosphere as carbon dioxide.

Lastly, when humans plow soil, some of the carbon that it stores is released as carbon dioxide into the atmosphere.

u hat yo w g 4. Usin about the know pH, how do d and crease ocean ink in i you th of carbonic levels ht affect igg acidd m e life? marin

256 | The Carbon Cycle

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STEMscopedia Corinne Le Quéré Climate Scientist

Born in Quebec, Corinne Le Quéré is renowned for exploring how carbon cycles through the atmosphere and ocean. During the COVID-19 pandemic, she gathered a team of 13 scientists from six different countries to try to get a picture of carbon dioxide emissions during the time when the world burned less fossil fuels.

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The Carbon Cycle | 257

STEMscopedia The same amount of carbon exists today as there has always been. It is not created or destroyed, just recycled throughout the spheres of Earth. Carbon is the basis of life on Earth. It’s in our bodies, our food, the air, the ocean, rocks, and other places. In the atmosphere, most carbon exists in the form of carbon dioxide, which helps to warm Earth and make life possible. The carbon cycle is the process that recycles carbon within and between organisms and their physical environments. Carbon cycles through Earth’s spheres in numerous ways, including photosynthesis, cellular respiration, decomposition, forest ¿ UHV YROFDQRHV DQG KXPDQ DFWLYLW\ 3URFHVVHV WKDW UHOHDVH FDUERQ LQWR WKH DWPRVSKHUH DUH FHOOXODU UHVSLUDWLRQ GHFRPSRVLWLRQ IRUHVW ¿ UHV volcanic eruptions, and human activities like burning fossil fuels and clearing land of trees to plant crops or build buildings.

Processes can also remove carbon from the atmosphere. Plants use carbon dioxide during photosynthesis, so they are an important way of removing it from the atmosphere. Trees and plants store carbon in their leaves, stems, and roots, making forests invaluable carbon storage systems.

Although volcanic eruptions release carbon into the atmosphere, the weathering process of lava rock can help to trap carbon.

Human activity contributes to the release of carbon dioxide into the atmosphere. Burning fossil fuels for energy releases large amounts of carbon. When humans cut down trees to clear forests, carbon is also released into the atmosphere. Because so much carbon is stored in soil, plowing can release large amounts of carbon as well.

Connect It So, if mass isn’t created or destroyed in a chemical reaction, what do you think this means in relation to the carbon cycle?

Chemical reactions are used to move carbon through the carbon cycle. Since mass isn’t created or destroyed, the mass of carbon in these reactions must be conserved. For example, when burning wood, the original mass of charcoal and oxygen equals the mass of ashes, soot, and gases produced. In other words, for the carbon reactions, the mass of the products is the same as the mass of the reactants. This is called the law of conservation of mass.

258 | The Carbon Cycle

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STEMscopedia 1

:KLFK VWDWHPHQW FRUUHFWO\ LGHQWL¿ HV D PDMRU GLIIHUHQFH EHWZHHQ ELRPDVV DQG IRVVLO IXHOV" A Biomass is made of living or recently living organisms.

B Biomass is composed only of animal parts.

C Fossil fuels form quickly over time.

D Biomass and fossil fuels are basically the same thing.

2

Fill in the appropriate terms to make the sentence correct: Cellular respiration ______ carbon dioxide to and from the atmosphere, while photosynthesis _______ carbon dioxide to and from the atmosphere.

A removes; reconstructs B returns; replaces C returns; removes D removes; returns

3

Which of the following can store large amounts of carbon?

A Plants B Soil C The ocean D All of the above

4

Humans exhale ______, which becomes a reactant in the process of ______.

A oxygen; photosynthesis B carbon dioxide; photosynthesis C oxygen; cellular respiration D carbon dioxide; cellular respiration

5

The law of conservation of energy states that energy cannot be created or destroyed; it can only change form or be transferred. Which of the following is evidence to support the law of conservation of energy found in all living systems?

A Most plants and animals begin their life cycles with small energy needs and gain more requirements as they develop.

B The total energy of all organisms remains the same over time.

C Decomposers transfer energy stored in the molecules of dead organisms to create new biomass for other organisms to feed on.

D The total mass of a dead organism equals the total mass of matter released to the environment by decomposition.

6

There are eight billion people in the world. Both people and animals exhale carbon dioxide. Yet scientists say that this exhaled carbon dioxide doesn’t contribute to warming temperatures on Earth.

How is it that carbon dioxide released from burning fossil fuels contributes to Earth’s warming but carbon dioxide exhaled from humans and animals does not?

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The Carbon Cycle | 259

GLOSSARY OF TERMS acid

bond

acid: a compound that produces hydrogen

atomic mass: the mass of an atom,

ions in solution, donates hydrogen ions, or

approximately equal to the number of

is an electron-pair acceptor

protons and neutrons in the atom

adenosine triphosphate (ATP): the

axis: the imaginary line through Earth that

primary molecule used by cells to store

extends from the North Pole to the South

chemical energy for use in cellular

Pole and is the center of Earth’s rotation

processes base: a compound that releases hydroxide agitation: the stirring or mixing of a

ions in solution, accepts hydrogen ions, or

solution so as to increase the particle

donates an electron pair

movement of the solute particles in solution biomass: material derived from living things aqueous solution: a solution in which the solvent is water

black hole: the remains of a star or other large object that collapsed under its own gravity

asteroids: large and small rocks or metallic

to form a superdense object with gravity so

masses orbiting the Sun; made up of materials strong that light cannot escape its pull similar to those that formed the planets bond: any of several forms of electrostatic atom: the smallest particle of an element;

attraction between atoms that hold the

made of electrons, protons, and neutrons

atoms together

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GLOSSARY OF TERMS carbon cycle

coefficient

carbon cycle: the continuous movement

chemical energy: energy stored in

of carbon in and between the abiotic and

chemical bonds and released through

biotic environments

chemical reactions

carbon dioxide: a gas that is a natural

chemical formula: a shorthand notation

component of the atmosphere; produced

that uses chemical symbols and numbers

by cells during cellular respiration and

as subscripts to represent the type and

used by plants and other organisms for

number of atoms that are present in the

photosynthesis

smallest unit of a substance

celestial objects: objects, such as planets,

chemical property: a characteristic that

moons, and stars, that are located in space

can be observed or measured only when atoms rearrange during a chemical change

cellular respiration: the process of obtaining energy from the breaking of

chemical reaction: the process by which

chemical bonds in nutrients

one or more substances change to produce one or more different substances

chemical change: a change that involves one substance being pulled apart or

chemical symbol: a one- or two-letter

combined with another substance to

notation used to represent an atom of a

form a completely different substance or

particular element

substances coefficient: a number placed in front of a chemical symbol or formula that represents the number of molecules 262

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GLOSSARY OF TERMS comet

electrical charge

comet: a celestial body of ice, dust, and

density: the amount of matter in a given

rock with an elongated and elliptical orbit

space or volume

compound: a new substance with unique

dilution: the process of reducing the ratio

chemical and physical properties formed

of solute to solvent in a solution

when two or more elements are chemically bonded during a chemical reaction

direct: in the shortest unbroken line; temperatures are higher where the Sun’s

concentration: a measurement of the

rays are direct

amount of solute that is dissolved in a given quantity of solvent

distance: a measure of how far apart two objects are

conductivity: a physical property that describes the ability of a substance to

economy: the management of the

transfer heat or electrical energy

resources of a community, country, etc., especially with a view to its productivity

culture: the quality in a person or society that arises from arts, manners, and scholarly electrical charge: a property of matter pursuits

determined by the number of positively charged protons and negatively charged

decomposers: organisms such as bacteria

electrons in a material

and fungi that break down the remains of dead plants and animals without need for internal digestion

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GLOSSARY OF TERMS electromagnetic radiation

gamma rays

electromagnetic radiation: the transfer

first quarter moon: when the right half of

of energy through matter or space as

the Moon is illuminated and the lunar cycle

electromagnetic waves, such as visible light

is in the waxing phase

and infrared waves force: a push or pull that can change the electromagnetic spectrum: a continuum

motion of an object

of all electromagnetic waves arranged according to frequency and wavelength,

fossil fuel: a natural nonrenewable fuel

from radio waves to gamma radiation

such as coal, oil, or natural gas formed a very long time ago from the remains of

electron: a negatively charged subatomic

living organisms

particle located in the electron cloud; involved in the formation of chemical bonds frequency: the number of wave cycles that pass electron cloud: the area surrounding the nucleus of an atom where the electrons

full moon: the lunar phase when Earth is

are found

between the Sun and the Moon and all of the illuminated portion is seen from Earth

element: a pure substance composed of the same type of atom throughout

galaxy: a large grouping of stars in space

energy: the ability of a system to do work;

gamma rays: electromagnetic waves

required for changes to happen within

with the shortest wavelengths, highest

a system

frequencies, and highest energy; produced by supernovas or the destruction of atoms

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GLOSSARY OF TERMS gas

inner planets

gas: a state of matter with indefinite volume Hertzsprung-Russell diagram: a plot of and shape

the surface temperature (color) of stars vs. their luminosity (brightness)

giant: a star with a larger diameter and lower surface temperature than an average

heterogeneous mixture: mixture that has

star; formed when the fuel center of an

ingredients combined but not uniformly

average star is depleted

mixed together

glucose: a sugar composed of six carbon

high tide: when the tide is at its greatest

atoms that is the preferred energy source

elevation

for most cells; produced by photosynthesis homogeneous mixture: mixture that has gravitational pull: the attraction between

ingredients uniformly mixed together

two objects due to the invisible force of gravity; the gravitational pull from the Moon

indirect: angled or spread out;

is primarily responsible for the tides that

temperatures are lower where the Sun’s rays

form on Earth

are indirect

gravity: the force that causes objects with

infrared waves: electromagnetic waves

mass to attract one another

with wavelengths longer than visible light but shorter than microwaves

hemisphere: half of a sphere; Earth and the celestial sphere can be divided into

inner planets: the rocky, terrestrial planets

northern and southern or eastern and

Mercury, Venus, Earth, and Mars, whose

western hemispheres

orbits are inside the asteroid belt

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GLOSSARY OF TERMS Kuiper Belt

metalloids

Kuiper Belt: the region of our solar system

luster: a physical property that describes

past Neptune; contains asteroids, comets,

the way the surface of a substance shines

and smaller bodies of ice

or reflects light, ranging between metallic (shiny) and nonmetallic (dull)

last or third quarter moon: when the left half of the Moon is illuminated and the lunar main sequence: category of stable stars in cycle is in the waning phase

the middle developmental phases that plot along a continuous diagonal belt on the

light-year: a unit of length equal to the

Hertzsprung-Russell diagram

distance that light travels through space in one year

malleability: a physical property that describes the ability of a material to be

liquid: a state of matter with a definite

permanently reshaped without breaking or

volume but no definite shape

cracking

low tide: when the tide is at its lowest

mass: a measure of how much matter is

elevation

present in a substance

luminosity: the intensity, or brightness, of

matter: anything that has volume and mass

light from a celestial body, which can be used to identify the body’s characteristics

metalloids: elements that have properties of both metals and nonmetals; sometimes referred to as semiconductors

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GLOSSARY OF TERMS metals

new moon

metals: elements that are typically solid,

neap tide: tide with the smallest daily tidal

shiny, malleable, and good conductors of

range; occurs when the Sun, Earth, and the

heat and electricity; includes most elements

Moon form a 90-degree angle

meteor: a small object that enters Earth’s

nebula: large cloud of gas and dust in

atmosphere from space and burns due to

interstellar space; the location of star

friction, emitting light

formation

microwaves: electromagnetic waves

neutral solution: a solution with a pH of 7

with wavelengths longer than infrared but shorter than radio waves

neutron: a neutrally charged subatomic particle located in the nucleus of an atom;

molecule: the simplest unit of a chemical

contributes to the mass of the atom

compound that can exist, formed when two or more atoms join together chemically

neutron star: the final stage of the life cycle for massive stars; formed after the star

moon: a celestial body that revolves around completely runs out of fuel and collapses a planet

every remaining proton in the core into a neutron

motion: the change in an object’s position with respect to time and in comparison

new moon: the lunar phase when the Moon

with the position of other objects used as

is between the Sun and Earth and none of

reference points

the illuminated portion is seen from Earth

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GLOSSARY OF TERMS nonmetals

physical change

nonmetals: elements that are typically not

Periodic Table of Elements: a table in

shiny, not malleable, and poor conductors

which all the known elements are arranged

of heat and electricity; usually gases or

by properties and are represented by

brittle solids

chemical symbols

nucleus: the tiny, very dense, positively

pH: a measure of the acidity or basicity of

charged region in the center of an atom that

an aqueous solution

is made up of protons and neutrons pH scale: a scale ranging from 0 to 14 that Oort cloud: the farthest portion of our

measures the concentration of hydrogen

solar system from the Sun; creates a three-

ions in a solution

dimensional sphere around the solar system; made of large chunks of ice

photosynthesis: a chemical reaction during which plants convert radiant energy

orbit: a curved path followed by a satellite

from the Sun to chemical energy; the

as it revolves around an object

reaction converts carbon dioxide and water into sugar (glucose) and oxygen

outer planets: the planets Jupiter, Uranus, Saturn, and Neptune, whose orbits lie

physical change: a change to a substance

beyond the asteroid belt

that occurs without forming a new substance, such as a change in size or state

oxygen: a gas produced by plants during

of matter

photosynthesis that animals use for respiration

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GLOSSARY OF TERMS physical property

reactant

physical property: a characteristic that can radiant energy: energy from the Sun that be observed or measured without changing

reaches Earth as visible light, ultraviolet

the substance

radiation, and infrared (heat) radiation

planet: a large celestial body that revolves

radiation: the transfer of energy by the

around a star in a solar system

movement of electromagnetic waves or subatomic particles

planetary nebula: a cloud of interstellar gas and dust created by a dying, average-

radio waves: electromagnetic waves

sized star

with the longest wavelengths, lowest frequencies, and lowest energy

product: a substance produced during a chemical reaction

rare earth elements: the group of metal elements that are used in almost all

properties: physical and chemical

technological devices

characteristics of matter used to describe or identify a substance

rate of dissolution: the speed at which a solute spreads out uniformly into a solvent

proton: a positively charged subatomic particle located in the nucleus of an atom;

reactant: a substance that takes part in

contributes to the mass of the atom

and undergoes change during a chemical reaction

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GLOSSARY OF TERMS reactivity

spring tide

reactivity: the ability of a chemical

solar system: a star and the group of

substance to undergo a chemical reaction;

planets and other celestial bodies that

significantly influenced by valence electrons

are held by its gravitational attraction and

of the reacting substances

revolve around it

relative density: the comparison of the

solid: a state of matter with definite volume

density of one material as it relates to

and shape

another; frequently, the comparison is to the density of water (as in sinking or

solute: a substance that dissolves in

floating)

another substance (solvent) to form a homogeneous mixture

revolution: the movement of one object around a center or another object

solution: a liquid mixture with a uniform composition formed when a solute is added

saturated solution: contains the

to a solvent

maximum amount of solute for a given amount of solvent at a constant

solvent: a substance in which another

temperature and pressure

substance (solute) is dissolved to form a homogeneous mixture

seasons: the four natural divisions of the year based on changes in temperature due to spring tide: tide with the largest daily tidal varying amounts of sunlight received (both

range, which occurs when the Sun, Earth,

intensity and number of daylight hours vary);

and the Moon line up with each other

caused by the tilt of Earth during its revolution 270

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GLOSSARY OF TERMS star

tilt

star: a celestial body consisting of a mass of supergiant: a star with a larger diameter gas held together by its own gravity in which and lower surface temperature than a the energy is generated by nuclear reactions massive star; formed when the fuel center of in its interior

a massive star is depleted

states of matter: distinct forms of matter

supernova: the death of a large star by

known in everyday experience; solid, liquid,

explosion

and gas; also referred to as phases surface area: the exposed area of a solid; structure: the arrangement of parts

expressed as squared units of length

subatomic particles: particles that are

temperature: average kinetic energy of all

smaller than the atom

the particles in a material; measured by a thermometer in degrees (usually degrees

subscript: a number written below and to

Celsius or degrees Fahrenheit)

the right of a chemical symbol that shows the number of a specific type of atom

tide: the rise and fall of sea levels caused by

present

the gravitational attraction of the Moon and the Sun

Sun: the luminous star around which Earth and other planets revolve; composed

tilt: the slant of Earth’s axis, which is

mainly of hydrogen and helium

23.5 degrees from vertical compared to Earth’s orbital plane around the Sun; results in the North Pole always pointing toward the North Star

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GLOSSARY OF TERMS ultraviolet waves

X-rays

ultraviolet waves: electromagnetic waves

white dwarf: the final stage of the life cycle

with wavelengths longer than X-rays but

for average stars; formed after a star expels

shorter than visible light waves; can cause

its outer material into a planetary nebula,

tans, sunburns, and skin cancers

leaving only the extremely hot, white core behind

universe: all of space and the matter space contains

X-rays: electromagnetic waves with wavelengths longer than gamma rays but

unsaturated solution: contains less

shorter than ultraviolet waves; used in

than the maximum amount of solute for

medicine and astronomy

a given amount of solvent at a constant temperature and pressure valence electrons: the electrons in the outermost energy level of an atom that influence how an element will react with other substances volume: a measure of the space that matter occupies wavelength: the distance between any two corresponding points on a wave, such as from crest to crest

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