Chapter 9, Problem 9.40QE

(a)

Interpretation Introduction

Interpretation:

The Lewis structure of ${\text{CN}}^{-}$ has to be determined.

Concept Introduction:

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.

A polar bond is a type of chemical bond where pair of electrons are unequally shared between two atoms. Polar molecules must contain polar bonds that form due to difference in electronegativity between the bonded atoms. The larger difference in electronegativity accounts for the more polar bond.

(b)

Interpretation Introduction

Interpretation:

The Lewis structure of ${\text{C}}_2{\text{F}}_4$ has to be determined.

Concept Introduction:

Refer to part (a).

(c)

Interpretation Introduction

Interpretation:

The Lewis structure of ${\text{CH}}_2\text{CHCN}$ has to be determined.

Concept Introduction:

Refer to part (a)