Chapter 10, Problem 10.83P

Interpretation Introduction

Interpretation:

Resonance structure of ${\text{N}}_3^{-}$ molecule is to be drawn, and also on the basis of resonance structure, the equal bond length of $\text{N}-\text{N}$ bond in ${\text{N}}_3^{-}$ but not in ${\text{HN}}_3$ is to be explained.

Concept introduction:

When bonds in a molecule can be expressed by different Lewis structures then resonance structures are used to depict the bonding in that molecule. These resonance structures have the same placement of atoms but different locations of bonding and lone pairs of electrons also one resonance form can be converted into another by moving lone pairs to bonding positions, and vice versa.

More important resonance structure selected as follows:

1. Always prefer smaller formal charge over the larger formal charge.

2. Always prefer the different non zero formal charge on adjacent atoms instead of the same non zero formal charge.

3. A more negative formal charge must be located on the most electronegative atom.

Formula to calculate the formal charge of the atom is as follows:

  $\text{Formal}\text{charge}=\left(\begin{array}{l}\text{number}\text{of}\\ \text{valence}\\ \text{electrons}\end{array}\right)-\left(\left(\begin{array}{l}\text{number}\text{of}\\ \text{non-bonding}\\ \text{electrons}\end{array}\right)+\left(\frac{1}{2}\right)\left(\begin{array}{l}\text{number}\text{of}\\ \text{bonding}\\ \text{electrons}\end{array}\right)\right)$        (1)