Chapter 5, Problem 2E

Interpretation Introduction

Interpretation: The Lewis structure of below $-1$ anionic species should be completed. Also, all the important resonance structures for $-1$ anionic species should be drawn.

  

Concept introduction: Lewis structure is representation of molecule in which dots are shown to represent unshared electrons and lines are shown to represent bonds. These lines and dots represent distribution of electrons in the molecule.

When one single structure is unable to describe all the properties of single molecule, a phenomenon called resonance comes into play. This arises when two or more than two Lewis structures are possible for one molecule. All such structures are called resonating structures and have same placement of atoms in them but these have different locations of bond pairs and lone pairs. The resonating structures are inter-convertible with each other. The resultant of all the resonating or contributing structures is called the resonance hybrid.

Rules to form resonance structure are as follows:

1. Use arrow types 1 and 2 for resonance structure of anions in movement of negative charge.

2. Use only arrow type 3 to move a positive charge for resonance structure of cations.

3. The sigma bond should not be broken. Any atom must not move from its place and total number of electrons must be same in all resonance structures.