What is the formal charge of { NO }_{ 2 }^{ - }?

To determine the formal charge of a molecule or ion, we need to compare the number of valence electrons in the neutral atom or molecule to the number of electrons assigned to it in the Lewis structure. The Lewis structure of nitrite ion, NO2-, can be represented as follows:

O
||
N=O
||
O-

In this structure, the nitrogen (N) atom is bonded to two oxygen (O) atoms, with one of the oxygen atoms carrying a negative charge. The oxygen atoms have a lone pair of electrons.

To calculate the formal charge, we use the formula:

Formal Charge = Valence Electrons - Assigned Electrons

For nitrogen (N):
Valence Electrons = 5 (group 15 element)
Assigned Electrons = 3 (1 bond with each oxygen)

Formal Charge on N = 5 - 3 = +2

For the oxygen atoms (O):
Valence Electrons = 6 (group 16 element)
Assigned Electrons = 4 (2 bonds + 2 lone pair electrons)

Formal Charge on each O = 6 - 4 = -2

Therefore, the formal charge of the nitrite ion, NO2-, is +2 on the nitrogen atom and -2 on each oxygen atom.