Chapter 1, Problem 46P

Each of the following species will be encountered at some point in this text. They all have the same number of electrons binding the same number of atoms and the same arrangement of bonds; they are isoelectronic. Specify which atoms, if any, bear a formal charge in the Lewis formula given and the net charge for each species.

$\text{:N}\equiv \text{N:}$

$\text{:C}\equiv \text{N:}$

$\text{:C}\equiv \text{C:}$

$\text{:N}\equiv \text{O:}$

$\text{:C}\equiv \text{O:}$

Interpretation Introduction

Interpretation:

For the given isoelectronic species, the formal charge on the atoms and the net charge on each species is to be determined.

Concept introduction:

Formula to calculate the formal charge on an atom:

$\text{Formal charge}=\text{Group number}-\text{electron count}$

$\text{Electron}\text{count}\text{=}\frac{\text{1}}{\text{2}}\text{(}\text{number}\text{of}\text{bonded}\text{electrons)}\text{+}\text{(number}\text{of}\text{unshared}\text{electrons)}$

In a molecule, the charge that is assigned to an atom is called the formal charge.

Answer to Problem 46P

Solution:

The formal charge is $0$.

The net charge on the species is $0.$

The formal charge on $\text{N}$ is $0$ and on $\text{C}$ is $-1$.

The net charge on the species is $-1.$

The formal charge on $\text{C}$ is $-1$.

The net charge on the species is $-2.$

The formal charge on $\text{N}$ is $0$ and on $\text{O}$ is $+1$.

The net charge on the species is $+1$.

The formal charge on $\text{C}$ is $-1$ and on $\text{O}$ is $+1$. The net charge on the species is $0$.

Explanation of Solution

(a) $\text{: N}\equiv \text{N :}$

Nitrogen belongs to Group $5\text{A}$ elements, thus the group number to be used for calculation is $5$. Each nitrogen atom has shared six electrons. There is one unshared electron pair on each nitrogen atom.

$\text{Electron}\text{count}\text{=}\frac{\text{1}}{\text{2}}\text{(6)}\text{+}\text{2}\text{=}\text{3}\text{+}\text{2=}\text{5}$

$\text{Formal}\text{charge}\text{=}\text{5}-\text{5}\text{=}\text{0}$

Since, both the nitrogen atoms have zero formal charge on them, the net charge of the species is also zero.

(b) $\text{: C}\equiv \text{N :}$

Carbon belongs to Group $4\text{A}$ while nitrogen belongs to Group $5\text{A}$ in the periodic table. The carbon and nitrogen atoms both have shared six electrons. There is one unshared electron pair on carbon and nitrogen atom.

For carbon atom,

$\text{Electron}\text{count}\text{=}\frac{\text{1}}{\text{2}}\text{(6)}\text{+}\text{2}\text{=}\text{3}\text{+}\text{2}\text{=}\text{5}$

$\text{Formal}\text{charge}\text{=}\text{4}-\text{5}\text{=}-\text{1}$

Hence, the formal charge on the carbon atom is $-1$.

For nitrogen atom,

$\text{Electron}\text{count}\text{=}\frac{\text{1}}{\text{2}}\text{(6)}\text{+}\text{2}\text{=}\text{3}\text{+}\text{2=}\text{5}$

$\text{Formal}\text{charge}\text{=}\text{5}-\text{5}\text{=}\text{0}$

Hence, the formal charge on nitrogen is $0$.

Therefore, the net charge on the species is $-\text{1}\text{+}\text{0}\text{=}-\text{1}$.

(c) $\text{: C}\equiv \text{C :}$

Carbon belongs to Group $4\text{A}$ in the periodic table. Each carbon atom has shared six electrons. There is one unshared electron pair on the carbon atom.

$\text{Electron}\text{count}\text{=}\frac{\text{1}}{\text{2}}\text{(6)}\text{+}\text{2=}\text{3}\text{+}\text{2}\text{=}\text{5}$

$\text{Formal}\text{charge}\text{=}\text{4}-\text{5}\text{=}-\text{1}$

Hence, the formal charge on each carbon atom is $-1$.

Therefore, the net charge on the species is $-1+(-1)=-2$.

(d) $\text{: N}\equiv \text{O :}$

Nitrogen belongs to Group $5\text{A}$ while oxygen belongs to Group $6\text{A}$ in the periodic table. The nitrogen and oxygen atoms have shared six electrons each. There is one unshared electron pair on nitrogen and oxygen atom.

For nitrogen atom,

$\text{Electron}\text{count}\text{=}\frac{\text{1}}{\text{2}}\text{(6)}\text{+}\text{2}\text{=}\text{3}\text{+}\text{2=}\text{5}$

$\text{Formal}\text{charge}\text{=}\text{5}-\text{5}\text{=}\text{0}$

Hence, the formal charge on nitrogen is $0$.

For oxygen atom,

$\text{Electron}\text{count}\text{=}\frac{\text{1}}{\text{2}}\text{(6)}\text{+}\text{2}\text{=}\text{3+}\text{2}\text{=}\text{5}$

$\text{Formal}\text{charge}\text{=}\text{6}-\text{5}\text{=}\text{+1}$

Hence, the formal charge on oxygen is $+1$.

Therefore, the net charge on the species is $0+(+1)=+1$.

(d) $\text{: C}\equiv \text{O :}$

Carbon belongs to Group $4\text{A}$ while oxygen belongs to Group $6\text{A}$ in the periodic table. The carbon and oxygen atoms have shared six electrons each. There is one unshared electron pair on carbon and oxygen atom.

For carbon atom,

$\text{Electron}\text{count}\text{=}\frac{\text{1}}{\text{2}}\text{(6)}\text{+}\text{2}\text{=}\text{3}\text{+}\text{2}\text{=}\text{5}$

$\text{Formal}\text{charge}\text{=}\text{4}-\text{5}\text{=}-\text{1}$

Hence, the formal charge on the carbon atom is $-1$.

For oxygen atom,

$\text{Electron}\text{count}\text{=}\frac{\text{1}}{\text{2}}\text{(6)}\text{+}\text{2}\text{=}\text{3}\text{+}\text{2=}\text{5}$

$\text{Formal}\text{charge}\text{=}6-\text{5}\text{=}+1$

Hence, the formal charge on oxygen is $+1$.

Therefore, the net charge on the species is $\text{-1}\text{+}(+1)\text{=}0$.