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The Atom Unit 4 How do we know that Atoms Exist?

Our Essential Question:

All year we will be trying to answer a simple question: What is everything made out of? Right now, we can say that everything is composed of matter. True, but it doesn’t tell us much. We also have heard that matter is composed of individual atoms. But‌how do we know that is true? People have been asking themselves that question ever since Democritus popularized the idea 2400 years ago. We will be asking ourselves the same question this week: How do we know that atoms exist? To help answer this question we will take a look at how this question has been answered historically up to 1907, at which point most scientists believed the evidence was overwhelming. We will also work together on a project to find modern visual evidence - real pictures - of individual atoms.

Day 1:

Day 2:

Day 3:

Day 4:

Day 5:

Here is the tentative plan: Lesson: History of the atom presentation. Lab: Seeing the atom web-based project day 1 of 2 Homework: History of the atom worksheet Lesson: The atom Lab: Seeing the atom web-based project day 2 of 2. Homework: Lesson: Percent composition, average atomic mass, and isotopic abundance Lab: Rehearse Seeing the Atom presentations Homework Lesson: AtomTest Review Lab: Seeing the Atom Presentations Homework: Review for test Atom Test Introduction to Unit 5: Electrons.

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The Atom How do we know that Unit 4 the world is made out A historical approach. of atoms? 400 BC

1907

What would convince you? write it below

1 Unit 3 Dr. B.’s ChemAdventure

Matter

The atom: Early Ideas Symbol Inventor

Idea The atom

Democritus

400 BC

Aristotle

Earth, air, fire, and water

400 BC

toxicology Paracelsus

1500 AD

Their Evidence:

Unit 3 Dr. B.’s ChemAdventure

Nothing!

2

Matter

2


First Evidence for the atom Mg + S

24 g 32 g

Mass is conserved Lavoisier

MgS

56 g

Atoms combine in small whole numbers

Dalton

3 Unit 3 Dr. B.’s ChemAdventure

Matter

• Mass percent ws

What is the atom made out of?

1. The Crooke’s Tube Mystery

4 Unit 3 Dr. B.’s ChemAdventure

Matter

3


Thomsons 1897 experiment: Are you convinced?

1. Bends “light”

2. Moves a propeller

3. 1000X smaller than a hydrogen atom • Proposes: The Electron • Thomson 5 Unit 3 Dr. B.’s ChemAdventure

Matter

Where are the electrons?

Rutherford’s 1907 Gold Foil Experiment Conclusion:

Most particles go right through the ultra-thin Gold foil.

Rutherford

nucleus

1. Electrons are outside the nucleus 2. The atom is mostly space But..No idea of electron organization 6

Unit 3 Dr. B.’s ChemAdventure

Matter

4


The atom. Evidence-based Ideas: Inventor Symbol Concept Mass is conserved

Lavoisier

Atoms combine in small whole numbers

Dalton

Electron

Thomson

Nucleus

Rutherford

7 Unit 3 Dr. B.’s ChemAdventure

Matter

d Rut her for

T ho mso n

Dal ton

isie r Lav o

lsus Par

ace

otle Aris t

Dem ocri tu

s

The atom: 400 BC-1907

• Brief video summary:1:00-1:57

Unit 3 Dr. B.’s ChemAdventure

8

Matter

5


Atomic Particles

• Video: 1:55-3:38

Particle

Charge

Mass #

Location

Electron

-1

0

cloud

Proton

+1

1

Nucleus

Neutron

0

1

Nucleus

Atomic Number = # of protons = Z “the blue number” 2He

Correct?

Yes

Unit 3 Dr. B.’s ChemAdventure

The atom song

Element

32S

# of protons = Z

Carbon

6

Phosphorus

15

Gold

79

No

9

Matter

Ions, Mass Number, and Isotopes

Protons Electrons

1 1

1 0

1

2

What is it?

H

H+ H-

+= cation -= anion

1. Ions: Different # of electrons.

3. Isotopes: Different

2.Mass Number

# of neutrons. Symbol

Protons + neutrons

p+

n0

e-

Oxygen - 18

8

10

8

Oxygen -

8

9

15

16

17

Phosphorus- 31 Unit 3 Dr. B.’s ChemAdventure

Mass # 18

8

17

15

31

18 8

O 17 8

31

O

P

10 15

Matter

6


Determination of average atomic mass

• Element X has 2 isotopes: • Isotope a 10 protons, 10 neutrons. • Abundance: 40%

• Isotope b has 10 protons 11 neutrons • Abundance: 60%

• What is the average atomic mass of Element X? • Solution: • (0.4)(20) + (0.6)(21) =

• 20.6 amu • a.a.m = sum of (abundance)(mass #) Unit 3 Dr. B.’s ChemAdventure

11

Matter

You try one: Element Guryanovium (Gu) • P N • 15 15 • 15 17

abundance Average Atomic Mass? 66% • 30.68 amu 34% How many neutrons is too many?:

The “Band of Stability” • In general •

n/p >1.5 = unstable = radioactive • All elements >82

Unit 3 Dr. B.’s ChemAdventure

Matter

Elements and isotopes video 3:40-7:40

12

Ions: 7:40-9:30

7


You try one: Element Guryanovium (Gu) • P N • 15 15 • 15 17

abundance Average Atomic Mass? 66% • 30.68 amu 34% How many neutrons is too many?:

The “Band of Stability” • In general •

n/p >1.5 = unstable = radioactive • All elements >82

Unit 3 Dr. B.’s ChemAdventure

Matter

Elements and isotopes video 3:40-7:40

12

Ions: 7:40-9:30

How do we know that atoms exist? Unit 3 Dr. B.’s ChemAdventure

Matter

d

Rut her for

mso n T ho

Dal ton

isie r Lav o

lsus P ar

ace

otle Aris t

Dem

ocri tu s

End Atoms. Next: Electrons 

13 video

8


Name__________________________________ Period________

lab4.1

How do we know that atoms exist? Images of the Atom Project 30 Points UPDATED 10/15/2008 Introduction All year we will be trying to answer a simple question: What is everything made out of? Right now, our best answer may be: everything is composed of matter. True, but it doesn’t tell us much. Another answer many be that all matter is composed of individual atoms. But…how do we know that is true? People have been asking themselves that question ever since Democritus popularized the idea 2400 years ago. We will be asking ourselves the same question this week: How do we know that atoms exist? To help answer this question we will take a look at how this question has been answered historically up to 1907, at which point most scientists believed the evidence was overwhelming. But most of you have indicated that the most convincing evidence for the existence of an atom would be to observe one. The goal of this project is to provide as much compelling visual evidence as you can that atoms do in fact exist. An important warning: Beware of doctored images on the web…anyone can create a fake image of an atom; we are looking for the real thing. A scoring rubric for this project is on the next page.

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Scoring Rubric for Seeing the Atom Powerpoints 30 Points Your score will be based on completing each step below. Use the 1989 IBM image as a model when preparing your 2 pages, and check off each item on the list below. 1. Topic Chosen from the list given on following page (2 points) Your own topic chosen: 5 bonus points 2. Two page PowerPoint on your topic Submitted in color (2 points) Page One: Includes at least 2 relevant atomic scale images on page 1 (2 points) Images are authentic images of atoms, and if not an explanation is given (2 points) An abstract (summary) is included (2 points) The identity of the atoms (carbon, xenon, etc.) is given (2 points) The images are sourced (2 points, see IBM sample for examples) Page Two: A narrative (no bullet-points) description of the research is given that includes: How this research provides evidence that atoms exist (2 points) The device used to create the image is given (2 points) The date of the research is given (2 points) Other interesting information of any type, such as information about the author of the work, is included (2 points) A minmum of three references are included (8 points; note high point value): These are not websites- they are either books or scientific journals They are properly formatted (see 1989 IBM image references for proper formatting) They are numbered as endnotes and cited in the text using superscripts that look like this.1 These powerpoint presentations will be printed in color, presented orally, and then posted in the room. Hopefully, they will help convince us what the scientists say is true: that all matter is made out of atoms. A sample presentation is provided to help you complete this project.

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Images of the Atom Project: Topics Here are some suggested topics that relate to actual images of atoms. Before choosing one, feel free to search the web so that you may discover your own topic. Five Bonus Points to any one who creates their own topic, or who defends the position that images of the atom are artificial: we have never seen the atom with these devices. 1. The 1989 IBM atomic image Suggested website: http://www-03.ibm.com/press/us/en/pressrelease/22260.wss 2. Silicon atoms imaged in 1981…the first images of the atom? Suggested website: http://www-03.ibm.com/press/us/en/photo/22264.wss 3. IBM’s molecular switch Suggested website: http://www-03.ibm.com/press/us/en/presskit/22242.wss 4. The worlds smallest abacus? Suggested website: http://www.research.ibm.com/atomic/nano/roomtemp.html 5. The first 3-dimensional images of atoms using MRI? 6. The scanning tunneling microscope 7. The atomic force microscope 8. The NIST atomic image and hip-hop atomic sound Suggested website: http://www.nist.gov/public_affairs/releases/hiphopatoms.htm 9. The Penn State atomic image 10. Observing the “wings” of atoms Suggested website: http://web.utah.edu/unews/releases/03/jun/orbitals.html 11. Simulation of a virus (note this is a simulation only, but state of the art) 12. Our government at work: atomic images from the National Institute of Science and Technology (NIST). Suggested website: http://www.metallurgy.nist.gov/facilities/TEMgallery.html 13. Gold and other atoms imaged by the National Center for Electron Microscopy Suggested website: http://ncem.lbl.gov/frames/tecnai.htm 14. Aluminum nitride images from Cornell University: Suggested website: http://www.cns.cornell.edu/Nanocharacterization06.html 15. Individual nickel atoms Suggested website: http://radio.weblogs.com/0105910/2004/09/06.html 16. Art and nanotechnology Suggested website: http://www.mrs.org/s_mrs/doc.asp?CID=1920&DID=171434 17. Kanji atomic image: Suggested website: http://www.nanopicoftheday.org/2003Pics/atomkanj.htm 18. Individual atoms on the surface of a microbe Suggested website:http://www.nature.com/nrmicro/journal/v2/n6/fig_tab/nrmicro905_F2.html 19. How big the atoms should be, relatively speaking Suggested website: http://www.camsoft.co.kr/CrystalMaker/support/tutorials/crystalmaker/resources/VFI_Atomic_ Radii_sm.jpg 20. The nanocar Suggested website: http://www.media.rice.edu/media/NewsBot.asp?MODE=VIEW&ID=7850

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Here is a completed presentation that can serve as a guide:

The 1989 IBM Atomic Image

By Your Name Here

Abstract: In 1989 Don Eigler from IBM ushered in the nanotechnology revolution by moving individual Xenon atoms to create the image shown above.

35 Xenon Atoms

Source: http://www-03.ibm.com/press/us/en/pressrelease/22260.wss

Eiglers Lab Notebook

Eigler with his STM Source: http://www.tainano.com/chin/Eigler.htm

Don Eigler (2006)

Source: http://www.theregister.co.uk/2006/06/13/don_eigler_valley/

Source: http://www.flickr.com/photos/jurvetson/456735511/in/set-30000/

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Don Eigler and the 1989 IBM Atomic Image The question “What is everything made out of” is one of the most fundamental questions of mankind, right up there with “Why are we here?”, and “Will that be on the test?”. Recorded ideas date back over 6000 years,1 first popularized in the west by the work of Democritus. Arguably the most compelling evidence for the atom being the fundamental particle of nature involves the human senses- smell, touch, sight, etc. Because of the small size of the atom, none of these are directly possible, so perhaps the next best thing is to observe it with the help of an instrument. This may have first occurred as early as 1981,2 but the image that popularized it was taken by Dr. Don Eigler in 1989.3 Don Eigler is a ponytailed, well educated physicist and surfer. In 1989, he designed his own scanning tunneling microscope. An image of him with his instrument was taken during a 2006 interview.4 While studying the surfaces of solids, he came up with the idea of limiting the movement of atoms by performing his experiments at a few degrees Kelvin- close to absolute zero. In his own words from the 2006 interview, he found that “Through a combination of hard work, some horse sense and good, old fashioned blind luck, I happened to be positioned to discover that I could manipulate individual atoms with a scanning tunneling microscope.” Having discovered the ability to move individual atoms, Eigler decided to create a work of art to document his discovery. What he created is an image of the letters I B M using the noble gas Xenon, a dense and unreactive colorless gas. Was he forced at gunpoint to do the bidding of his IBM bosses?? According to Eigler: “I made that decision on my own. Management never said anything to me beforehand, and I did it with a very clear purpose in my mind. IBM gave me a job, gave me the opportunity when I needed one, gave me the opportunity to excel at doing the things that I love in life, and it was payback time. I pull no punches on that. It was my way of giving back to the corporation some of what the corporation gave to me.” Does Eigler get bored recounting the discovery, now that two decades have passed? “I don't mind talking to people when they're curious, for instance, about what I was thinking about or why did I do this or something like that. The thing is that I always get introduced to people as the guy who wrote I-B-M in atoms. After you have heard that enough times, you don't really need to hear it five more times.” Eiglers current interests are in the field of Spintronics,5 a speculative field where future computers will be based not electricity (the translational movement of electrons) but on their spin…a sort of electricity where the electrons stay where they are. Sources: 1. Gangopadhyaya, Mrinalkanti (1981). Indian Atomism: History and Sources. Atlantic Highlands, NJ: Humanities Press. ISBN 0-391-02177. 2. G. Binnig, H. Rohrer “Scanning tunneling microscopy” IBM Journal of Research and Development 30,4 (1986) reprinted 44,½ Jan/Mar (2000). Available on the web at http://researchweb.watson.ibm.com/journal/rd/441/binnig.pdf 3. Imaging Xe with a low-temperature scanning tunneling microscope. DM Eigler, PS Weiss, EK Schweizer, ND Lang - Physical Review Letters, 1991 1189-1192. 4. A man and his microscope: IBM's quest to make atom-sized chips. The silver surfer speaks. Ashlee Vance, The Register, June 13, 2006. Available on the web at http://www.theregister.co.uk/2006/06/13/don_eigler_valley/ 5 Spintronics: A Spin-Based Electronics Vision for the Future. S. A. Wolf et al., Science 2001, Vol. 294. no. 5546, pp. 1488 - 1495

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Name_________________________________________ Period______

4ws4.1

History of the atom worksheet Complete this worksheet after listening to the presentation on the history of the atom from 400 BC to 1907 AD. Refer to the notes on your slides if you need to for each question. 1. What is the essential question for this course? 2. What is the essential question for this unit? 3. What would you need to see, know, or observe to become convinced that atoms exist?

4. By now you have seen a presentation on some ideas and experiments concerning the atom from about 2400 BC to 1907. Fill in the table below to summarize the work and significance of some of the key players. name

Democritus

Aristotle

Paracelsus

Lavoisier

Dalton

Thomson

Rutherford

Symbol

Contribution

5. How is Daltons model of the atom different from that of Democritus?

6. Draw a picture of the Cathode Ray tube used by Thomson:

7. What happened when Thomson put a magnet near the Cathode Ray Tube?

8. Why was that important? 14


9. How big is an electron compared to a hydrogen atom?

10. Draw a figure and explain Rutherford’s Gold foil experiment:

11. Lavoisier’s experiments indicated that mass is never lost when chemical reactions occur. Daltons experiments suggested that elements come in different sizes, and they combine in simple ratios. Thomson showed there is something smaller than hydrogen, and Rutherford showed that there is a lot of empty space in matter. Still, some scientists did not accept at that point that atoms exist. Put yourself in their shoes. Write a paragraph stating why this is still not enough evidence to prove that atoms exist.

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Name______________________________Period_________________

WS4.2

Atomic Bookkeeping Worksheet:

Atomic Particles, Atomic Number, Mass Number, Ions, and Isotopes Here are some quick facts to help you keep track of the names and numbers associated with the atom:

Protons are in the nucleus, each has a +1 charge, and identifies the element. Neutrons are in the nucleus, each has no charge, and determines the isotope. Electrons are outside the nucleus, each has a -1 charge, and determines the reactivity. Atomic Number is the number of protons. Mass number is the number of protons + neutrons Average atomic mass is the averaged mass for a mixture of isotopes An ion has either more or less electrons than protons, so it is charged. Isotopes vary only in the number of neutrons for an element. 1. Pick an element, any element. My element has the symbol _______, which stands for ____________. It has ______ protons, and when uncharged also has _________ electrons. The average atomic mass of this element is ________ atomic mass units. If it has one extra electron, this would give it a _____ charge. If one atom had two more neutrons than protons, the mass number would be ________ atomic mass units. 2. Fill in the blanks below: Hydrogen 1 H 1.008

____________average atomic mass ____________chemical symbol ____________chemical name ____________atomic number

3. Complete the following table: Element O (oxygen) Zn (zinc)3+ Sn (tin)Fe (iron)3+ C (carbon) H (hydrogen)+ Sg (seaborgium)

Number of protons 8

Number of electrons

Average atomic mass 15.999

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4 What is an isotope? 5. What is the difference between mass number and atomic number? 6. Draw the complete symbol for the isotope of silver that contains 47 protons and 60 neutrons: 7. Complete the following table. (Note that here we are calculating the mass number for that particular isotope. This is not the average atomic mass) Element Number of Number of Number of Mass number protons electrons neutrons 2+ C (carbon) 6 6 10 12 26 57 Hg (mercury) 204

8. What is the difference between mass number and average atomic mass?

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Name______________________________

Period__________________________

WS4.3

Atomic mass/average atomic mass worksheet

1. Complete the following table: Element Number of protons O (oxygen) 8 Zn (zinc) Sn (tin) Fe (iron) C (carbon) H-(hydride) Note the negative sign! Sg (seaborgium)

Number of electrons 8

Number of neutrons 9 37

Mass number 17 118

30 14 0

266

2. Mass number and atomic number are easy to confuse. To determine atomic number one only needs to know the number of _____________, whereas the mass number also includes the number of_____________. 3. Chlorine has two naturally occurring isotopes, Cl-35 and Cl-37. The lighter isotope is _____ which contains _____ protons and _____ neutrons. The heavier isotope is _______ with _____ protons and _____ neutrons. 4. Here is a problem that is solved for you. As you read the problem, imagine how you could solve it without a calculator, then see how it is done, and apply the solution to #5. An imaginary element X has two isotopes, one with a mass of 20 atomic mass units (amu), and the other with a mass of 22 amu. They both occur with equal (50%) abundance. What is the average atomic mass of X? Solution: (0.5)(20) + (0.5)(22) = 21 a.m.u. 5. What would the atomic mass of element X above be if the abundances of X-20 was 25%, and the abundance of X-22 was 75%? Solution (fill in the missing numbers: ( )( ) +( )( ) = _____ a.m.u. 6. Silver has 2 isotopes. One has a mass of 106.905 amu (52%) and the other has a mass of 108.905 amu (48%). What is the average atomic mass of this isotopic mixture of silver?

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Name______________________________ Period__________________________

WS4.4

Isotopes, ions, atomic mass, and average atomic mass worksheet The number of protons, electrons, and neutrons is usually symbolized in an element box in the following manner: For example: 235 41 Mass number

19

(p + + n 0) 24

Charge (p + + e -)

9

Na+

F-

2+

Ca

20

U

92

11

9 protons 10 neutrons 10 electrons

atomic number (p + )

20 protons 21 neutrons 18 electrons

92 protons 143 neutrons 92 electrons

Once the number of each atomic particle is known, it is an easy matter to identify isotopes (atoms that vary only in the number of neutrons) or ions (atoms that do not have the same number of protons and electrons). 1. Fill in the blanks

34

35

16

17

S

___protons ___ neutrons ___electrons

Cl

-

238

6+

U

92

___protons ___protons ___ neutrons ___ neutrons ___electrons ___electrons

32

35

238

16

17

92

S

Cl

4+

U

___protons ___ neutrons ___electrons

___protons ___protons ___ neutrons ___ neutrons ___electrons ___electrons

7 protons 9 neutrons 8 electrons

105 protons 8 protons 132 neutrons 8 neutrons 106 electrons 8electrons

2. Which pairs of elements are isotopes?

3. Which elements are ions? 4. Fill in the boxes below.

1 protons 0 neutrons 1 electron

23 protons 24 neutrons 22 electrons

5 protons 6 neutrons 8 electrons

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5. Are the following pairs of compounds isotopes, ions, or different elements? Also, provide the full atomic symbol for each substance 20 Example: Ne 10 a. Substance 1: 10 protons, 10 neutrons, 10 electrons: b. substance 1: 10 protons, 11 neutrons, 10 electrons Relationship: isotopes

21

Ne

10

c. Substance 1: 10 protons, 10 neutrons, 10 electrons d. substance 1: 9 protons, 10 neutrons, 10 electrons Relationship:________________ e. Substance 1: 10 protons, 10 neutrons, 11 electrons f. substance 1: 10 protons, 10 neutrons, 10 electrons Relationship:________________ 6. Determine the average atomic mass for the following imaginary elements, using the first question as an example.

Solved Example. Isotope 1: 4 protons, 4 neutrons. Abundance : 91% Isotope 2: 4 protons, 5 neutrons. Abundance : 9% Average atomic mass = sum of (abundances)(mass number) = (0.91)(8 amu) + (0.09)(9 amu) = 8.09 amu a. Isotope 1: 14 protons, 14 neutrons. Abundance: 62% Isotope 2: 14 protons, 16 neutrons. Abundance : 38% Average atomic mass =

b. isotope 1: 94 protons,104 neutrons. Abundance : 52% Isotope 2: 94 protons, 112 neutrons. Abundance: 48% Average atomic mass =

c. Isotope 1: 24 protons, 24 neutrons. Abundance : 40% Isotope 2: 24 protons, 25 neutrons. Abundance : 39% Isotope 3 : 24 protons, 28 neutrons abundance = 21% Average atomic mass =

3. Level One Only: Boron has two naturally occurring isotopes. Boron -10 (abundance = 19.8%; mass = 10.013 amu) and another isotope (abundance 80.2%). The average atomic mass of boron is 10.811 amu. What is the mass of the other isotope? 20


How to ace the Atom unit

Howtoaceitunit4

In this our fourth unit, we explored the atom. Our goal was to answer the question: How do we know that atoms exist? We began with a chronological study, starting with the ideas of Democritus, and ending with the discovery of the nucleus by Rutherford. We also considered what it would take to convince us that atoms in fact do exist, and we found evidence that atoms have been individually observed and moved. We then focused on the three primary subatomic particles. We considered their location, mass and charge, and this led to an understanding of atomic number, mass number, and average atomic mass. Finally, we applied this to isotopes, and finished with the band of stability- the ratio of protons to neutrons for a stable atomic nucleus. In our next unit we will focus on the subatomic particle that determines the chemical behavior of each element: the electron. To ace this unit you should review the powerpoint slides, the atom worksheets, and this study guide. You should also review the results of our Seeing the Atom project. Here are some quick questions on each topic we covered. 1. The history of the discovery of the atom: a. Aristotle and his four “elements� b. Democritus: symbol and what he got right c. Paracelsus: Symbol and contribution d. Lavoisier: Symbol, contribution, and his untimely end e. Dalton: symbol and his major contribution f. Thomson: symbol, what he discovered, device he used, evidence . g. Rutherford: symbol, and his key experiment 2. The 3 subatomic particles, their mass in atomic mass units (amu), and charges

3. Atomic number

Example: What are the atomic numbers for each element in baking soda, NaHCO3? Why can Magnesium never have 13 protons?

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4. Mass number

Example: What is the mass number of an oxygen atom that has 8 neutrons and 9 protons?

5. Average atomic mass formula

Example: Element X has two isotopes. One has an abundance of 63% and an atomic mass of 10 a.m.u. The other has an abundance of 37% and an atomic mass of 15 a.m.u. What is the average atomic mass of element X?

6. Isotopes- definition (watch out for cases that are different elements, not different isotopes)

Example: How many protons and neutrons are present in an atom of Cs-111?

7. Ions- know how to calculate charge on an atom

Example: How many protons, neutrons, and electrons are present in an atom of C-13?

Example: Draw element boxes that show an example of a fluoride monoanion (-1), and a calcium dication (+2).

8. Nuclear stability

Example: Circle the stable isotopes: U-238 Po-208 C-14 9. Chemical symbols for elements 1-20

What are the symbols for

hydrogen, helium, lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine, neon, sodium, magnesium, aluminum, silicon, phosphorus, sulfur, chlorine, argon, potassium, and calcium,? 10. How do you know that atoms exist? Provide quantitative evidence in addition to imaging. Be sure to review the Seeing the Atom Presentations from each of you. Good luck on the test. 22


d. chapter 4 Atom Packet