Question

How many resonance structures does N3- have?

Answer 1

I find three. But the one marjed with "*" below is more stable because it avouds putting two formal charges on either nitrogen atom.

Explanation:

`:N\equivN-N:`

`:N=N=N:` *

`:N-N\equivN:`

Carbon dioxide has a similar set of resononce structures. In both cases the delocalization makes each bond more stable than an isolated double bond between the same two atoms would be.