Transcript AP Review Unit 1

Review Unit 1
Atomic Theory, Atomic Structure,
Quantum Mechanics,
and Periodicity
Copyright 2004 - John Sayles
1
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
2
– MASS relationshipCopyright 2004 - John Sayles
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

Copyright 2004 - John Sayles
3
Atomic Structure

Atoms made of p+, n, e– p+ ~ 1amu

n ~ 1amu
e- ~ 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 eCopyright 2004 - John Sayles
4
Quantum Mechanics
Wave<-->Particle duality leads us to treat eas 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

Copyright 2004 - John Sayles
5
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

ml = magnetic spin QN = gives specific orbital
– Restricted to -l,…,0,…+l

ms = spin QN = allows only 2 e- per orbital
– Restricted to +1/2 or -1/2
Copyright 2004 - John Sayles
6
QM - Aufbau Principles

Fill lowest energy orbitals first
– 2nd 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
Copyright 2004 - John Sayles
7
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 eCopyright 2004 - John Sayles
8
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
Copyright 2004 - John Sayles
9
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 2s1, Na is 3s1, K is 4s1, Rb is 5s1, etc…

Valence is repeated in the same way
– All alkali metals are +1
Copyright 2004 - John Sayles
10
Atomic radius
The father of all periodic properties
 In explaining the other trends, you’ll always
get back to radius and Coulomb

– Fes attraction = k Q1Q2/r2
Def’n: distance from nucleus to outermost e Trends:

– increases down family (no surprise)
– Decreases across period (¿que?)
Copyright 2004 - John Sayles
11
Explaining Atomic Radius
Vertical trend is easy; adding entire shell of e Horizontal trend is trickier

– Shielding: Inner shell e- shield the valence efrom 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
Copyright 2004 - John Sayles
12
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
Copyright 2004 - John Sayles
13
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
Copyright 2004 - John Sayles
14
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
Copyright 2004 - John Sayles
15
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
Copyright 2004 - John Sayles
16