Chapter 9, Problem 9.105QE

Interpretation Introduction

Interpretation:

The Lewis structure of ${\text{N}}_{\text{2}}\text{O}$ and ${\text{NO}}_2$ has to be drawn. Also, the structure that has unpaired electrons and shorter $\text{NO}$ bond has to be determined.

Concept Introduction:

A covalent bond is a bond that is formed from the mutual sharing of electrons between atoms. Lewis structures are representations of the covalent bond. In this, Lewis symbols show how the valence electrons are present in the molecule.

Steps to write Lewis structures are as follows:

1. The skeleton structure with single bonds between all bonded atoms has to be written

2. Sum the valence electrons of the atoms in the molecule.

(a) For cations, one electron is subtracted for each positive charge.

(b) For anions, one electron is added for each negative charge.

3. Subtract two electrons from total number of valence electrons for each bond in the skeleton structure.

4. Count the number of electrons required to satisfy the octet rule for each atom in the structure. If the number of electrons needed is less than the number remaining, add one bond for every two electrons needed between atoms to attain an octet.

5. The remaining electrons are placed as lone pairs on atoms that need them to satisfy the octet rule.

The formula to calculate formal charge of atom is,

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

Some molecules do not have only one Lewis structure. The Lewis structures that differ only in the arrangement of multiple bonds are called resonance structures.

Resonance structure comprises of two or more Lewis Structures that describes the arrangement of bond of a single species and include fractional bonds and fractional charges.