In the nitrite ion (NO₂^–), a single covalent bond connects one oxygen (O) atom with the nitrogen (N) atom. Another oxygen atom is bonded to the nitrogen by a double covalent bond. There are two resonance structures.

O^–-N=O ↔ O=N-O^–

Let us calculate the formal charges on the atoms and determine the formal charge of NO₂^–.

i. O^–-N=O

Nitrogen

V = 5, N = 2, B = 6

Therefore,

q_f = 5 – 2 – 6/2 = 0

Oxygen 1

V = 6, N = 6, B = 2

Therefore,

q_f = 6 – 6 – 2/2 = -1

Oxygen 2

V = 6, N = 4, B = 4

Therefore,

q_f = 6 – 4 – 4/2 = 0

The net formal charge is: 0 -1 + 0 = -1

ii. O=N-O^–

Nitrogen

V = 5, N = 2, B = 6

Therefore,

q_f = 5 – 2 – 6/2 = 0

Oxygen 1

V = 6, N = 4, B = 4

Therefore,

q_f = 6 – 4 – 4/2 = 0

Oxygen 2

V = 6, N = 6, B = 2

Therefore,

q_f = 6 – 6 – 2/2 = -1

The net formal charge is: 0 + 0 – 1 = -1

The two resonance structures of the nitrite ion form a hybrid with formal charge equal to -1.