Physical Chemistry Heteroatomic Molecular Orbitals Page 2
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2Example 2: hydrogen fluoride
Example 2: hydrogen fluoride
Finding ground configuration
Bond-order
10 electrons
1 is a
nonbonding orbital
Fill molecular orbitals in order
2 is a
nonbonding orbital
2
2
2
4
1
2
3
1
1 is a
nonbonding orbital
3 is a
bonding orbital
Eigenvalues with respect to operations
= 0 (all shells filled)
Consider only bonding and antibonding
S = 0 (all shells filled)
electrons
Even under reflection in vertical plane
Term symbol
1
BO
2 (
) 0
1
1
HF
2
Example 3: hydrogen fluoride
Example 4: Nitric oxide, NO
Excited configuration found by promoting a single
Fifteen (15) electrons
electron
Use heteroatomic filling order
2
2
2
3
1
1
2
3
1
4
2
2
2
2
4
2
1
Eigenvalues of operators
1
2
3
4
1
5 (
)
2 (
)
Treat 3 electrons like 1 electron
“The state of a hole is the state of an electron.”
Leads to term
= 1
S = ½
S = 0, 1 (either paired or unpaired)
Terms that arise from this configuration
Results ground-state term
1
3
2
Summary
Heteroatomic molecules are analyzed in a
manner similar to homoatomic molecules
Must know MOs
Must know filling order
MOs are more complex
Must involve atomic orbitals of similar energy and
symmetry
Energies calculated by computer
Hartree-Fock calculation relatively straightforward
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