Question

Consider the possible structures of the N ion shown below + N=N=N-NEN 2 :N-NEN-NEN NEN-N-NEN N-N=N=N=N 5 NEN-N-N-N N=N-NEN-N: Based on formal charges, which structure ( #2 or #3) is the less likely arrangement of the electrons? Based on formal charges, which structure (#5 or #6 ) is a more likely arrangement of the electrons? What is the formal charge on the central nitrogen atom in structure 1? How many of the structures above represent likely arrangements for the electrons in Ng?

Answer 1

Formula of formal charge:

F.C = Number of electron N should have ( = 5) - [2 x no. of lone pairs + no. of bond pairs]

Based on the formula, we can get the forrmal charges of all N atom present here (numbering from left),

Structure	F.C (N1)	F.C (N2)	F.C (N3)	F.C (N4)	F.C (N5)
1	-1	+1	0	+1	0
2	-2	+1	+1	+1	0
3	0	+1	-1	+1	0
4	-1	+1	+1	+1	-1
5	0	+1	0	+1	-1
6	0	+1	+1	+1	-2

The idea is, more distributed the formal charge is, the more is the contribution of the resonating structure. Also the most likely structures are those, which have less number of formal charge in distributive manner.

• Among 2 and 3, since in 3 the F.C is more distributed, so, 2 is less likely.
• Among 5 and 6, since in 5 the F.C is more distributed, so, 5 is more likely.
• From the table we get the F.C of N3 for structure 1 is 0.
• The structures having less number of F.C but more distributed F.C are, 1,3 and 5. So, the number of such structures are 3.