How many resonance structures does N−3 have?

The N−3 ion, also known as nitride ion, has a total of two resonance structures. The nitride ion has a triple bond between the nitrogen atom (N) and the three valence electrons. The two resonance structures arise due to the delocalization of the lone pair of electrons on the nitrogen atom.

In one resonance structure, the lone pair is localized on one of the nitrogen atoms, while in the other resonance structure, the lone pair is delocalized over all three nitrogen atoms. The two resonance structures can be represented as follows:

Resonance Structure 1:
:N≡N: ⇌ [N−3]

Resonance Structure 2:
:N≡N: ⇌ [N−3]

The actual structure of the nitride ion is a resonance hybrid of these two contributing structures, with the electrons delocalized over the entire ion.