Valence Bond and Molecular Orbital theories

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Valence Bond and Molecular Orbital theories

• Chem. 562
• Spring, 2004
• UW, Madison

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Potential energy curve
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Potential energy curves are important
Excited electronic states
Ground electronic state
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Valence Bond Theory
Many electron w.f. in terms of atomic orbitals
(A.O.) Pairing electrons in overlapping A.O. of
appropriate symmetry
Linus Carl Pauling (1901-1994) Nobel prizes
1954, 1962
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VB wavefunctionof H2
2
1
z
a
b
z1z2
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VB energies of H2
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sp2 Hybrid atomic orbitals
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sp3 Hybrid atomic orbitals
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sp Hybrid atomic orbitals
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Multiple bonds with VB
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Multiple bonds with VB
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Molecular Orbital Theory
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Molecular Orbitals
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The He dimer
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The Li dimer
s2s
2sA
2sB
s2s
s1s
1sA
1sB
s1s
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Molecular Orbitals from p A.O.s
NOTE Symmetry is important in forming M.O. from
A.O.s (LCAO)
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Molecular Orbitals from p A.O.s
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Electron configurations for diatoms
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Electron configurations for diatoms
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M.O.s from O2
s1s
s1s
s2s
s2s
p2p
s2p
p2p
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Heteronuclear diatomics
x
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Heteronuclear diatomics
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Heteronuclear diatomics
LiH
CH
HF
CH
HF
CH
HF
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Polyatomic molecules
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More complicated molecules
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Modern MO calculations
W. Kohn (1923-)
J. A. Pople (1925-2004)
Nobel prize in Chemistry 1998