Question

Azide ion $\left(N_3{}^{-}\right)$ exhibits on $N-N$ bond order of 2 and may be represented by resonance structures I, II and III given below.
$:\stackrel{-}{\underset{..}{N}}=\stackrel{+}{N}=\stackrel{-}{\underset{..}{N}}:⟷{}^{2-}:\ddot{\underset{..}{N}}-\stackrel{+}{N}\equiv N:⟷:N\equiv \stackrel{+}{N}-\ddot{\underset{..}{N}}{:}^{2-}$
I II III
Select correct statements.

• A. Structures I and II make greater contributions than III
• B. Structures II and III make smaller contributions than I
• C. Structures I and II make greater contributions than II
• D. All the three structures make equal contributions

Answer 1

Answer: (B)

Structures II and III make smaller contributions than I

In the resonance structures of the azide ion, structures II and III make smaller contributions than I.
Resonance structure I has just one unit of formal charge on each nitrogen.
Resonance structures II and III have large formal charge of -2 on one of the nitrogens.
Such a large charge on a small atom like nitrogen makes structures II and III less favorable.
And count less to the "true" representation of the azide anion, than resonance structure I.