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Prof. Edoardo Garrone

Chemistry course 2011


Contact: Dipartimento di Scienze dei Materiali ed Ingegneria Chimica (going to change) e-mail: edoardo.garrone@polito.it phone number: 011-090-4661


The course (8 credits) comprises: - 58 hours of teaching - 18 hours of exercises given by myself (not this week!)


Two groups (squadre): Group 1 from Ma to Sun Tuesday 11.30 room 1B Group 2 from Tabansi to Zhouang Tuesday 10.00 room 2B


Timetable


- 3 hours practical laboratory - Two hours of tutoring each week by the teacher: each Monday at 15.00 in my office. Send a mail before coming


Statistics show that only 50 % of students pass the exam within the first year: study hard! And in a clever way!


Those of you who have particular problems (for instance never studied chemistry) please contact me


Most important problem: LANGUAGE! • Many of you do not know English enough • In Chemistry there are many words to be known • In the future, many courses will be in Italian, so you need to learn also the words of Chemistry in Italian


Many words in science come from ancient Greek (like polymer) or Latin (like Ferrum, iron) British English and American English sometimes do not coincide, either in: • the word used (Italian benzina is gasoline in USA and petrol in UK) • writing S is sulfur in USA and sulphur in UK • pronunciation (CH3- is mithàil in UK and méthil in USA)


The text of the lessons (Powerpoint presentations) are available as pdf files on the Politecnico site. Check that you can access the site The content of the lessons is enough for passing the examination


Warnings: - the notes are in English - some words are also given in Italian (usually in red), when important words are involved, and these are different in the two languages


IMPORTANT ADVICE Students are invited: • to unload the text of the lessons (pdf files) before each lesson • to read them carefully in advance • to check all words they do not know


The number of textbook in Chemistry is very large and none is adopted in particular Hereafter some of them are listed A good textbook from secondary school can also be useful


 P. Atkins, L. Jones PRINCIPI DI CHIMICA Zanichelli Ed.  M. Silbelberg (in English) CHEMISTRY McGraw-Hill Ed.  A. Delmastro, D. Mazza, S. Ronchetti QUIZ DI CHIMICA Soc. Editrice Esculapio Bologna E. Giamello, L. Battezzati, V. Bolis, B. Fubini ATOMI, MOLECOLE, MATERIALI Loescher Ed. L. Palmisano, M. Schiavello ELEMENTI DI CHIMICA EdiSES


You may find useful material material at http://didattica-online.polito.it Enter the section Chimica For copyright reasons some movies require USENAME : studente (student) PASSWORD: na6021023


Exam: two parts a) written test: basically a quiz (multiple entry questions), but also open questions and exercises b) If the written test is passed with a mark greater than (or equal to) 17/30, the student is admitted to the oral part


Example of written text (in Italian for the moment)


Ignorance is not admitted of: • the nomenclature (both Italian and English) • the chemical formula of the most common chemical compounds (e.g. nitric acid, sulphuric acid, etc)


Questions?


Introduction to Chemistry


Where chemistry comes from: • prehistory: discover of fire (combustion) • Neolithic: metallurgical processes • about 6000 years ago: pottery (ceramica), tissues, glass (vetro) • about 3000 b.C. : making of wine and beer • Greeks and Arabs: philosophical approach to the study of nature and composition of matter (theory of four elements: air, fire, water (acqua), earth)


• for 15 centuries, until the end of medieval ages: alchemy (search for the philosophical stone, able to convert any matter into gold!) • since 16th century chemistry as a science. Boyle (gas law) is considered the father of Chemistry. He wrote “The sceptical Chemist”

Nobody knows the origin of the word Chemistry: • some say CHINESE!!! • alchemy is the Arabic version


Chemistry today The study of the structure and properties of substances, and the reactions by which a substance turns into another Indeed this is a course on the Structure of Matter!


Basically an experimental science, developing independently from Physics up to the 30’s - in the 30’s, after the development of quantum mechanics (QM): understanding of laws of Chemistry on the basis of quantum mechanics


- now possible to solve Schroedinger equation for molecules even complex, i.e. to calculate via computers the structure and properties of compounds - even of non stable molecules (in the interstellar space!)


Still necessary to interpret data coming from computations with chemical concepts, discussed in this course!


Knowledge on isolated atoms is important, though they seldom exist alone! Chemistry is basically a reductionist science (the properties of the whole are inferred from those of the constituent parts) Example: the molecule H-Cl can be described by knowing the properties of the atoms H and Cl when isolated NB: not always so! Example: aromaticity in organic molecules is a collective phenomenon


Two main tools in discussing atomic properties:

- periodic table

- atomic orbitals


BASIC DEFINITIONS IN CHEMISTRY


Matter (Materia): what makes up the universe. Energy (energia): ability of doing work Up to Einstein (1905), two distinct concepts Now related one another through the famous formula:

EINSTEIN RELATIONSHIP

ΔE = Δm. c2


elementary substances PURE SUBSTANCES

compounds

Fixed chemical composition

MATTER (System) Homogeneous systems MIXTURES variable chemical composition

Heterogeous systems


System: System portion of space with matter and energy in it

Heterogenous (eterogeneo) system: as opposed to homogeneous (omogeneo) Homogeneous system: has the same physical and chemical properties everywhere, at a scale larger than 10-6 cm (dimensions of atoms‌)


Homogeneous system: brass (ottone), an alloy of copper and zinc (lega di rame e zinco)

Heteroge neous system: Granite rock (granito) (mixture of feldspat, mica, quartz)


Homogeneous system: constant composition? Yes: substance (sostanza) No: solution (soluzione) if liquid

If solid: alloy (lega)

Mild separation techniques: e.g. evaporation of solution


chemical compound Substance element Separation of components in a compound: requires strong physical methods (e.g. electrolysis) At the atomic level: Element: substance made up of atoms all equal Chemical compound: substance made up by different atoms with constant proportions!


Phase A pure substance may be found as a homogeneous system (monophasic: only one phase, e.g. liquid water) or as a heterogeneous system (polyphasic, e.g. coexisting liquid water and ice). The chemical nature of water is the same!

Some physical property is different: density!

Ice is less dense than water, so it floats‌


AGGREGATION STATES OF SUBSTANCES

IODINE (IODIO)

BROMINE (BROMO) CHLORINE (CLORO)


The aggregation state of a substance depends on the physical parameters (pression, temperature)

SOLID

LIQUID

GASEOUS


Some phase transitions (transizioni di fase) SÆ L LÆS

melting (fusione) solidification

SÆV

sublimation

VÆ S

condensation

LÆ V

evaporation

VÆ L

liquefaction

S = solid L = liquid V = vapour (English) Vapor (American)


Element: as the word implies, a substance which cannot be transformed into others… Each element has a SYMBOL A one or two-letter symbol is enough to denote the element How many the elements? about one hundred…

Why? A fist big question…


Sodium is Na (Latin Natrium), Potassium is K (Latin Kalium) Iron is Fe (Latin Ferrum, Italian Ferro) Nitrogen is N (Italian Azoto) Copper is Cu (Italian Rame) Tin is Sn (Latin Stannum, Italian Stagno) Lead is Pb (Latin Plumbum, Italian Piombo) Mercury is Hg (Latin Hydrargyrium) Pay attention to “false friends”: Carbon is C and not Ca (Calcium) Silicon is Si (Italian Silicio, not silicone, a family of polymers…) Phosphor is P (Italian Fosforo)


Elemento

% peso

1 H 1 4 He 2

71 27 1.8 0.2

C,N,O,Ne Tutti gli altri

98

C,N,O,Ne 1,8%

Tutti gli altri 0,2%

He 27,0% H He

Chemical composition of the Universe

C,N,O,Ne Tutti gli altri H 71,0%


Composi tion of the earth crust


Composition of the earth crust 99,5 % of the earth crust is given by 12 elements, not comprising C and N, on which is based the organic chemistry and biochemical compounds 99,95 % is given by 24 elements All others (ca. 68) are 0.05%


Masses for a body about 70 kg

Composition of the human body


ATOM: smallest portion of an element still having the same properties. From the Greek “atomos�: not cleavable

Indeed: cleaved under very energetic conditions, typical of nuclear reactions!


Atoms are the basic unit forming the substances, the elementary bricks of matter. Each ELEMENT gives rise to distinct atoms. About 90 elements are natural and about 19 artificial, to a total of about 109 elements, i.e. to about 109 different types of atoms Isolated atoms are spherical and very small. Typical dimension of atoms: 10 -10 meter (1 Ă…, Angstrom ) or 0.1 nanometres or 100 picometers. Chemists use Angstroms!!


Three constituents in atoms: - Protons (positive charge) at the nucleus - Neutrons (charge-less) at the nucleus - Electrons (negative charge) around the nucleus


Protons and Neutrons are also called nucleons, because they stay at the nucleus


The mass is basically concentrated in the nucleus (with positive charge). The rest is filled with negative charge. Atoms are basically empty: Nuclear radius ≅ 10-5 atomic radius (nuclear volume ≅ 10-15 atomic volume). If an atom was the size of a football pitch (campo da calcio), the nucleus would be the size of the ball!!


ELEMENTARY PARTICLES IN ATOMS Nucleus: PROTONS and NEUTRONS The volume outside the nucleus is occupied by ELECTRONS

This is 4He


NB: this is a pictorial description Elementary particles are no balls‌ Elementary particles (in particular electrons) are both waves and particles‌


The electron is 1840 times lighter than the proton! This much lower mass explains why they span a much larger space! (like planets around the Sun…)

Neutrons held the protons together in the nucleus: “strong” nuclear force overcoming electrostatic repulsion…


How do we know about the structure of atoms?


Electric discharges in rarefied gases: the electron

All gases yield the same “cathodic� rays: the ratio e/m is measured when a magnetic field is applied


Electric discharges in rarefied gases: the electron With a bored cathode the positive counterparts are revealed


The measurement of e, the charge of the electron (Millikan experiment)


The discovery of the atomic nucleus (Rutherford)

Deflexions observed are compatible only with a model implying the mass of the atom concentrated in a very small volume, the nucleus. Comparison between the mass of the nucleus and its charge lead to hypothesing the existence of neutrons, observed years after.


Îą particles deflection (atoms are basically empty!)


MASS AND CHARGE OF ELEMENTARY PARTICLES

Massa (Kg)

Carica ©

Massa (u) Carica (e)

PROTONE

1.67262 10-27 1.60218 10-19 1.00728

+1

NEUTRONE

1.67493 10-27 0

0

1.00866

ELETTRONE 9.10939 10-31 -1.60218 10-19 0.00055

-1


ATOMIC NUMBER, MASS NUMBER, ISOTOPES ATOMIC NUMBER Z : number of protons of an atom An element is designated by Z: all atoms of the same element have the same Z. However, elements are usually designated not by Z but by a one-two letter symbol Sy. MASS NUMBER A: the sum of protons and neutrons A – Z is the number of neutrons: not fixed given a value of Z! Atoms with same Z (same element) with different A are ISOTOPES


An atom is characterised by both Z and A. The complete notation is:

A

ZSy

Usually Z is omitted (not necessary). A indicated only if required.


If we are not interested in isotopes, then the atom is characterised by Z, the number of protons in the nucleus: Z is also the number of electrons of the neutral atom This latter definition is much more important in chemistry!


ISOTOPES PROTIUM

1H 1

DEUTERIUM

2H 1

TRITIUM

3H 1


Correlation between (A – Z) number of neutrons and Z, number of protons


Not all values of Z and A-Z are possible Nuclei are stable up to Z = 83 (Bismuth). For Z > 83, e.g. Po Z = 84, nuclei become unstable and undergo nuclear reactions The number of elements is finite because nuclei become unstable radioactive decay: unstable nuclei transform through emission of particles For light nuclei Z ~ A – Z (up to Z = 20)


how do we weight atoms?

Ionisation chamber

with MS, mass spectrometry • for the electron (e/m) • for atoms • also for molecules The particle, carrying a charge e and having a speed v, is deviated by the electromagnetic field

detector


MASS OF AN ATOM M One would expect additivity: M = Z mp + (A-Z) mn + Z me Instead: M < Z mp + (A-Z) mn + Z me Defect of mass!! Why? Relativistic Effect: mass defect measures the binding energy among nucleons EINSTEIN RELATIONSHIP

ΔE = Δm. c2


if we study the average binding energy per nucleon: ∆E = c2 ([Z mp + (A-Z) mn + Z me] – M)/A

∆E

A


56Fe

is the most stable nucleus is the divide between: - lighter nuclei which release energy by fusion (fusione), e.g. (4 H Ă&#x2020; He) as in stars - heavier nuclei which release energy by fission (scissione), e.g. Uranium as in the Hiroshima bomb


Because of the defect of mass, neither the mass of a proton or of a neutron can be the unit mass. Need for a common unit mass for atoms: amu

1amu is one twelfth of the mass of carbon 12 1 amu = 1.6605 10-27 Kg Close to, but smaller than mp and mn 1 gr/amu defines Avogadroâ&#x20AC;&#x2122;s number!


So far a single atom: from now on, a large setâ&#x20AC;Ś What mass must be attributed to atoms in a large set? An average valueâ&#x20AC;Ś


Atomic mass (or ATOMIC WEIGHT, peso atomico) is the average of the masses of the possible isotopes, weighed on NATURAL ABUNDANCES H

1H

= 99.985% 1.007825 u

2H

(D) = 0.015% 2.04102 u

Average atomic mass of H H = 0.99985 x 1.007825 + 0.00015 x 2.014102 amu = 1.00797 amu


Average atomic mass for C 12 C 6

98.89%; 136C 1.11% Over 10000 atoms, 9889 are 126C and 111 136C p.a. = 9889 .12 + 111 . 13 = 12.01 10000 Average atomic mass for Cl 35 Cl 17

75.53%; 3717Cl 24.47 p.a. = 7553 .35 + 2447 . 37 = 35.5 10000


35

17Cl

28

75.53%; 3717Cl 24.47%

14Si

92.21%; 2914Si 4.70%; 3014Si 3.09%


LIST OF SOME ATOMIC MASSES


What happens if I consider the mass in grams of different elements equal to its atomic weight? The same number of atoms is involved…

The MOLE is the unit of measure (in the S.I. system) of the amount of matter. A mole of objects (atoms, molecules…) is made up by an Avogadro’s number of objects (N = 6.02.1023 mol-1).


Pb

Hg S

Cr Al

Cu

Mg


Quite a general definition: one could speak of a mole of eggs… (dozens are more practical…) - An Avogadro’s number of photons is called one Einstein - An Avogadro’s number of electrons carries a charge called one Faraday


Let us consider the reaction:

H

1 atom 1.01 amu 1.69 . 10-24g

+

Cl

Ă&#x2020;

1 atom 35.5 amu 59.1 . 10-24g

HCl

1 molecule 36.5 amu 60.8 . 10-24g

1.69.10-24g. N =1.01 g 59.1.10-24g. N =35.5 g

Masses are additive

60.52.10-24g. N =36.5

Moles are not additive. In this case: 1 + 1 mole makes 1 mole


Chemistry polito  

Cintroduction to polito chemitry

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