Fred J' Grieman

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Fred J. Grieman
Atomic properties to consider when forming
molecules Measurement of atomic orbital
energies Periodic Properties Prediction based
on Coulombic Interactions Ionization
energy Electron affinity Atom size
Electronegativity
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Measurement of orbital energies First Remember
photoelectric effect light absorbed by metal
ejects electrons
Vary light energy E h? No e- until e h?o ?
(work function/
binding energy) Increase light energy E
h? gt ? Ek(e-) h? - ? Increase energy of
light increase Ek(e-) Apply to atoms
except Many binding energies energy of
orbitals Use fixed energy of light
Ek
E
h?
Work function
h?o
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Measurement of orbital energies Photoelectron
Spectroscopy
Measurement of orbital energies Photoelectron
Spectroscopy
Measurement of orbital energies Photoelectron
Spectroscopy
ionization region
Know E h? exactly Measure Ek (e-) Orbital
energy h? - Ek (e-) (Binding Energy ?)
different Ek (e-)
orbital energy
h?
2p
2s
E
?Esubshell 2 Ry
?Eshell 60 Ry
1s
1s 2s

2p
Example Ne h?
? es (1s) (2s) (2p)
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Fig. 17-5
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• Periodic properties
• Basis
• Ep (q1q2)/r12 Coulombs Law
• Ep (-e)(Ze)/r -Ze2/r H-like atom
• Ep (-e) (Zeffe)/r -Zeffe2/r e- in
  multi-electron atom
• Ep (-e)(-e)/r e2/r e- - e- repulsion
• Actual Properties
• Ionization energy
• Electron affinity
• Atom size
• Electronegativity

charges
distance between charges
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First Ionization Energy A(g) energy (IE1) ?
A(g) e-
Second Ionization Energy A(g) energy (IE2) ?
A2(g) e- (Fig. 17-6)
IE ? as Z ? e- ? r from nucleus
Predictions across period
down group change period
IE ?, Z ?, but r ? e- screened
IE ? dramatically, r ? greatly
Small changes?
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Fig. 17-6
Z increases, but e-/e- repulsion
2s22p3 ? 2s22p4
Z increases, but E(2p)gtE2s
2s2 ? 2s22p1
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Electron Affinity Attraction of e- to neutral
atom A(g) e- ? A-(g) energy (Electron
attachment energy) (exothermic) ?75 atoms exo
?25 endo Electron Affinity EA - (Electron
attachment energy)
Predictions across period
More exothermic as Z ? so EA increases across
period
Why?
Exceptions Be (EA lt 0), N (EA lt 0) and P
EA for nobel gases? EA lt 0 (endothermic)
np3 ? np4 e-/e- repulsion
2s2 ? 2s22p1 E(2p) gt E(2s)
EA(Cl) gt EA(F) ? Small F atom, greater
e repulsion
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Atom and Ion Size Important b/c atom size affects
structure of solids, polarizability
Atomic radius Metals metallic radius Nonmetals
covalent radius Ions ionic radius All
estimates
Predictions Group Period
r? as n?
r? as Z ?
Ionic Radii r(Na).98Å r(Na)1.91Å r(F-)1.36Å
r(F)0.64Å Na ? K ? Rb .98Å ? 1.31Å
? 1.45Å ?r .33Å .14Å ?r decreases due to
filling d orbitals
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Electronegativity
Measure of shared electron attraction to atom
in molecular bond
Mulliken-Jaffe Scale Based on atomic
properties EN constant (IE1EA) (EN
electronegativity)
Pauling Scale
Based on molecular properties BE(AB)
(BE bond energy)
BE(AA).BE(BB)1/2 96.48(EN(A) EN(B)2
shared electron ionic
part of bond Assumptions ionic part increases
BE and is due to
electronegativity difference Set
EN(F) 4.0 (Actually, 3.98)
O (3.4) F (3.9) S (2.7) Cl (3.1)
Br (3.0)
O (3.5) F (4.0) S (2.5) Cl (3.0) Br (2.8)
Pauling Scale preferred
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Increasing Electronnegativity
Next apply atomic properties to the formation
of molecules
Electronegativity Predictions? Across period Down
group
EN ? as Z ?
EN ? as n ?
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Exam next Wednesday (Mon. Lab reports due
Thurs.) Chapters 15, 16, 17-1 QA Session
Monday 815 945