56
Chapter 4 Valence-Bond Structures for some Diatomic and related Molecules
Figure 4-1: Schematic contours for σ2p, σ*2p, x

and
*
x
 molecular orbitals.
Figure 4-2: Energy levels for n = 2 homonuclear molecular orbitals.
bond structure for a doubly-occupied bonding molecular orbital (cf. Eqn. 3-5),
which is equivalent to the covalent-ionic resonance formulation A•─•A ↔
(-) A‫׃‬ A
(+) ↔
(+) A ‫׃‬A
(-) .
Table 4-1: Molecular orbital configurations and valence-bond structures for diatomic molecule ground-states, and an 2
O excited state (
*
2
O ). (For
*
2
O , 2
O
 and 2
O
 , degenerate configurations are not reported here, see also Figure 4-3).
σ2s
σ*2s
x

y

σ2p
*
x

*
y

σ*2p
n
2
Li
2
1
Li—Li
2
Be
2
2
0
:Be Be:
2
B
2
2
1
1
1
X
X
:B B:
2
C
2
2
2
2
2
:C C:

2
N
2
2
2
2
2
3
:N N:

2
O
2
2
2
2
2
1
1
2
X O X
O
X
X
:O — O:
*
2
O
2
2
2
2
2
2
2
:O O:

 
2
2
O
 , 2
F
2
2
2
2
2
2
2
1
( )
( )
:O— O:, :F — F:


   
 
 
2
O

2
2
2
2
2
1
2.5
1
1
2
2
(
) (
)
X O X
: O
O :



2
O

2
2
2
2
2
2
1
1.5
1
1
2
2
(
)
(
)
O
X
X
: O — O :



