5 Steps to a 5 AP Chemistry

written with a two-headed arrow (↔) between them. Figure 11.11 shows the three resonance
forms of the nitrate ion.

Again, let us emphasize that the actual structure of the nitrate is not any of the three
shown. Neither is it flipping back and forth among the three. It is an average of all three.
All the bonds are the same, intermediate between single bonds and double bonds in
strength and length.

Bonding  157

Increasing Energy

Atomic

Orbital

of O

Atomic

Orbital

of O

2 p

2 s 2 s

2 p

Molecular

Orbital

of O 2

σ

ππ

σ∗

σ∗

π∗ π∗

σ

Figure 11.10 Molecular orbital diagram of valence-shell electrons of O 2.

O O

O

N

−

O O

O

N

−

O O

O

N

−

Figure 11.11 Resonance structures of the nitrate ion, NO 3 −.