Chapter 10.1, Problem 10.4BFP

Interpretation Introduction

Interpretation:

Resonance forms of thiocyanate ion, ${\text{SCN}}^{-}$ with the most important resonance form using formal charge, is to be determined.

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 resonances structure have the same placement of atoms but different locations of bonding and lone pairs of electrons also one resonance form can be converted intoanother 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)