1. Copyright 2004 - John Sayles1 Review Unit 1 Atomic Theory, Atomic Structure, Quantum Mechanics, and Periodicity

2. Copyright 2004 - John Sayles 2 Evidence for Atoms Law of Constant Composition –Water is always 8 grams O for every 1 gram H –MASS relationship Law of Conservation of Mass –Mass of products = Mass of reactants –MASS relationship –Not obeyed in nuclear processes Law of Multiple Proportions –Mass ratio of C/O in carbon monoxide divided by mass ratio of C/O in carbon dioxide is a small whole number –Ratio of mass ratios is a small whole number –MASS relationship

3. Copyright 2004 - John Sayles 3 Postulates of Atomic Theory Matter is composed of atoms. –Formerly thought to be indivisible Elements are composed of only one type of atom. Compounds are composed of 2 or more types of atoms chemically combined. Chemical reaction is a rearrangement of atoms

4. Copyright 2004 - John Sayles 4 Atomic Structure Atoms made of p +, n, e - –p + ~ 1amun ~ 1amue - ~ 0 amu e - are the most important component –Arranged in shells, as per QM History of atomic models –Dalton: indivisible atom; meteorological data –Thompsen: plum-pudding model with e - ; Crooke’s tube –Rutherford: planetary model; Gold foil exp’t –Bohr: quantized atom; based on Spectro data –Schrodinger: QM; applied wave physics to the e-

5. Copyright 2004 - John Sayles 5 Quantum Mechanics Wave Particle duality leads us to treat e - as waves, not as particles with trajectory Each e - has wave eq’n, , built by considering all PE’s and KE’s of the e -   2 gives probability density = orbital picture  H  gives Energy of the e -   gives rise to 4 quantum numbers

6. Copyright 2004 - John Sayles 6 Quantum Numbers n = principal QN = gives energy level –Restricted to 1,2,3 … l = angular momentum QN = gives orbital –Restricted to 0,1,2 … n-1 m l = magnetic spin QN = gives specific orbital –Restricted to -l,…,0,…+l m s = spin QN = allows only 2 e - per orbital –Restricted to +1/2 or -1/2

7. Copyright 2004 - John Sayles 7 QM - Aufbau Principles Fill lowest energy orbitals first –2 nd law of Thermodynamics e - spread out among degenerate orbitals –Hund’s Rule of Maximum Multiplicity –Like to have lots of unpaired e - ’s with parallel spins Only 2 e - ’s per orbital –Pauli Exclusion Principle says you can’t have identical e - ’s in an atom –Having two diff. spins allows the 2 e - ’s in an orbital to be non-identical

8. Copyright 2004 - John Sayles 8 QM Miscellaneous Heisenberg Uncertainty Principle –Determining the position of an e - changes its momentum and vice-versa –Mathematically,(∆x)(∆p)=h/(4π) Magnetic properties –Ferromagnetism is conventional magnetism –Paramagnetism is caused by unpaired e - with parallel spins –Diamagnetism is due to the absence of unpaired e -

9. Copyright 2004 - John Sayles 9 Periodicity Periodic Law: when elements are arranged in order of increasing atomic number, many of their properties repeat in a periodic manner (Dmitri Mendeleev) For each periodic property, we need –Definition –Trends down family/group and across period –Explanation of both trends

10. Copyright 2004 - John Sayles 10 Electron Configuration (Valence) Electron config is the mother of all periodic properties Every 2,8,18,32 elements we get another element with the same e - config –Li is 2s 1, Na is 3s 1, K is 4s 1, Rb is 5s 1, etc… Valence is repeated in the same way –All alkali metals are +1

11. Copyright 2004 - John Sayles 11 Atomic radius The father of all periodic properties In explaining the other trends, you’ll always get back to radius and Coulomb –F es attraction = k Q 1 Q 2 /r 2 Def’n: distance from nucleus to outermost e - Trends: –increases down family (no surprise) –Decreases across period (¿que?)

12. Copyright 2004 - John Sayles 12 Explaining Atomic Radius Vertical trend is easy; adding entire shell of e - Horizontal trend is trickier –Shielding: Inner shell e - shield the valence e - from the pull of the nucleus –Effective Nuclear Charge: the pull the valence e - ’s feel is the actual nuclear charge - # of shielding e - –Effective nuclear charge increases across a period, therefore radius decreases

13. Copyright 2004 - John Sayles 13 Ionization Energy Def’n: Energy needed to remove outermost e - Trends: –Decreases down family –Increases across period Explanation –Outer e - in large atom is farther away and therefore less tightly held –Fr has lowest IE (biggest r); F has ~ highest

14. Copyright 2004 - John Sayles 14 Electron Affinity Def’n: Energy released when an atom gains an e - –Opposite of IE Trends: –Decreases down family –Increases across period Explanation –Smaller radius atoms grab e - more tightly

15. Copyright 2004 - John Sayles 15 Electronegativity Def’n: scale created to indicate an atoms ability to attract e - Similar to electron affinity Trends and explanation same as for EA Useful later for predicting –Whether ionic or covalent bonds will form and –How polar a covalent bond will be

16. Copyright 2004 - John Sayles 16 Mettalic Character Def’n: metals are –Shiny (have luster) –Conduct heat and electricity –Are malleable and ductile (opposite of brittle) –React by losing e - ’s Trends –MC increases down family –MC decreases across period –Metals are at lower left of the staircase Explanation: large atoms lose e - ’s better