F. J. Grieman

1
F. J. Grieman
Molecular Theory 2 Chemical Bonding (1) Atom
Review Lowest energy from multiple
interaction Ionic bond Covalent bond Polar
covalent Ionic character Electronegativity and
type of bond Bonding Model Requirements
2
Atomic Structure Review
electron interference ?
wavefunctions
H.U.P Quantized Energy ?
probability
Orbitals
Energy, shape, direction, nodes, phase, squares
give probability n l ml
n, ml ,- P ?2 x Volume
Multielectron Atom
3 interactions
e nuc e-e spin
Energy f(? Q.s)
f(n, l)

• E large when change n noble gas stability
• small when change l

Pauli and Hund ? electron configuration
Periodic Table table ? atomic electronic
structure metals give off es easily
nonmetals accepts es easily periodic
properties explained by orbital occupation
3
Molecules
Model formed from atoms that maintain identity
Molecules properties can be very different than
atoms
How?
Interactions
e-nuc
e - e
nuc - nuc
intraatom
interatom
spin
Why do systems seek lowest energy?
Lowest energy is our guide
Understand from thermodynamics

• ball on hill

Energy released to surroundings
Organized energy
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Molecule
A B ? AB enough energy to
fall apart AB ? AB energy to
surroundings (disorganized)
(stable molecule formed) AB energy
(organized) ? AB ? A B
(minimum energy required Bond Dissociation
Energy) Equilibrium A B ? AB
energy Possible ways to
form molecules
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ionic combine IE, EA, Coulombic
Attraction energy Na(g) ? Na(g) e-
IE1 495 kJ/mol Cl(g)
e- ? Cl-(g) energy -EA
-349 kJ/mol --------------------------------------
--------------------------------------------- Na(g
) Cl(g) ? Na(g) Cl-(g) E
146 kJ/mol (endothermic!) Na(g)
Cl-(g) ? NaCl- (molecule)
Coulombic Attraction E (2.31 x 10-19
Jnm/molecule) Q1Q2/r(nm)
(1.39 x 102
kJnm/mol) Q1Q2/r(nm) r(Na) r(Cl-) .095
.181 .276 nm (solid)
r .251 nm (gas) E(Coulomb)
-554kJ/mol BE(NaCl) (-554) (146)
-408 kJ/mol Graph Interaction In 1986, the
Nobel Prize in Chemistry was shared by three
physical chemists. Two were Americans, Dudley R.
Herschbach, Yuan T. Lee, John C. Polanyi were
awarded for discoveries that helped to
explain the physical dynamics of chemical
reactions. harpoon mechanism
D. R. Herschbach, Reactive scattering in
molecular beams, Adv. Chem. Phys.,


VOL 10, pp. 319-393,
1966. See also this link.
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Cl2 ?? Cl energy ? Cl e-
1255 kJ/mol IE1 Cl e- ? Cl-
energy -349 kJ/mol -EA --------------------
--------------------------------------- Cl Cl
? Cl Cl- 906 kJ/mol
!!!!!! Coulombic Energy r(Cl2) .151 nm just to
break even !! But r(Cl-) .181 nm !!!! Cl
would have to be inside Cl- !!!!! Must be
something else Covalent bonding electron
sharing somehow Must let lowest Ep be our
guide right now (Economics Analogy Demonstration
and Graph)
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hetero molecules somewhere between covalent
and ionic Ionic ? Polar covalent ?
covalent Polar?? From dipole (two poles)

-
Dipole moment ? (e?)R (e?) amount of
charge separated by distance R Measure in Debye
3.336 x 10-30 Cm
Measure of extent of ionic bonding Calculate
?(calc) for complete charge transfer e.g.,
NaCl- ?(actual)/?(calc) x 100 Ionic
character NaCl ?(actual) 9.00 D ?(calc)
(1.60 x10-19 C)(2.51 x 10-10 m)/3.336 x 10-30
Cm/D) 12.0 D e?
R conversion Ionic
Character 9.00/12.0 (100) 75
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• (Cl2) 0 further evidence that covalent
• Ionic gt 50 considered ionic compound
• Electronegativity (EN) indicator of ionic
  extent
• The greater ?EN, the more ionic
• Molecule Cl-Cl HCl NaCl
• EN 3.0/3.0
  2.1/3.0 0.9/3.0
• ?EN 0 0.9 2.1
• covalent polar ionic
• Polar covalent example HCl (gas phase!!!)
• ? H?Cl ?- ?(actual) 1.11 D r(HCl)
  0.1275 nm
• ?(calc) 6.12 D Ionic Character
  (1.11/6.12)100 18.2
• polar covalent

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• Bonding Model should explain and/or predict
• Which molecules are stable
• Relative strengths of bonds
• Relative Bond lengths
• Ionic/covalent nature of bonds
• Polyatomic structure

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Fridays Lecture in another room to be
determined. Exam Wednesday Closed book bring
calculator pencils Memorization En, Ry ao
size and energy
of atoms Energy of
Light, de Broglie Wavelength Chapters 15
(except 15-4), 16, 17-1 Conceptual as well as
working problems Short answer or fill in to
show you understand concepts can apply
them QA Session tonight, Seaver N Aud. 815
945