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

Copyright 2004 - John Sayles 1

Review Unit 1Review Unit 1

Atomic Theory, Atomic Structure,

Quantum Mechanics,

and Periodicity


Evidence for AtomsEvidence 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


Postulates of Atomic TheoryPostulates 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


Atomic StructureAtomic 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 e-


Quantum MechanicsQuantum 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


Quantum NumbersQuantum 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


QM - Aufbau PrinciplesQM - 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


QM MiscellaneousQM 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-


PeriodicityPeriodicity

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


Electron Configuration (Valence)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


Atomic radiusAtomic radius

The father of all periodic propertiesIn 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?)


Explaining Atomic RadiusExplaining 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


Ionization EnergyIonization 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


Electron AffinityElectron 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


ElectronegativityElectronegativity

Def’n: scale created to indicate an atoms ability to attract e-

Similar to electron affinityTrends and explanation same as for EAUseful later for predicting

– Whether ionic or covalent bonds will form and– How polar a covalent bond will be


Mettalic CharacterMettalic 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

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