Chapter 2, Problem 2.2E

Interpretation Introduction

Interpretation:

Three Lewis structures of ${\text{OCN}}^{-}$ that follow octet rule has to be drawn and structure that is most important has to be identified.

Concept Introduction:

Lewis structures represent covalent bonds and describe valence electrons configuration of atoms. The covalent bonds are depicted by lines and unshared electron pairs by pairs of dots. The sequence to write Lewis structure of some molecule is given as follows:

• The central atom is identified and various other atoms are arranged around it. This central atom so chosen is often the least electronegative.
• Total valence electrons is estimated.
• single bond is first placed between each atom pair.
• The electrons left can be allocated as unshared electron pairs or as multiple bonds around the right symbol of the element to satisfy the octet (or duplet) for each atom.
• Add charge on the overall structure in case of polyatomic cation or anion.

The formal charge on each atom in the Lewis structure can be calculated from the equation written as follows:

    $\text{Formal charge}=\left[V-L-\frac{1}{2}B\right]$

Here,

$V$ denotes valence electrons in free atom.

$L$ denotes electrons present as lone pairs.

$B$ denotes electrons present as bond pairs.