Question

Question: Assign formal charges to each N and O atom in the given molecules. All lone pairs have been drawn in.

a.

b.

c.

d.

Short answer

Answer

a. -1

b. -1, +1, -1 (from left to right)

c. +1

d. 0, 0 (N and O, respectively)

Step-by-step solution

Step-by-Step Solution Step 1:  Determination of formal charge  

The determination of formal charge is completed by using the given formula:

$\mathbf{Formal}\mathbf{}\mathbf{charge}\mathbf{}\mathbf{=}\mathbf{}\left(\mathrm{valence}{e}^{-}\right)\mathbf{-}\left(\mathrm{lone}\mathrm{pair}\mathrm{of}{e}^{-}\right)\mathbf{-}\left(\frac{1}{2}\times \mathrm{bonding}\mathrm{pair}\mathrm{of}{e}^{-}\right)$

Calculation of formal charge

. The calculation of the formal charge of N is as follows:

• The total number of valence electrons of nitrogen is five.
• The lone pair of electrons is four.
• The bonding pair of the electrons is four as all the N electrons are used.

Therefore,

$\begin{array}{rcl}\mathrm{Formal}\mathrm{charge}\mathrm{of}\mathrm{N}& =& 5-4-\frac{1}{2}\times 4\\ & =& 5-4-2\\ & =& -1\end{array}$

Hence, the formal charge of N is -1.

b. The calculation of the formal charge for N (extreme left) is as follows:

• The total number of valence electrons of N is five.
• The lone pair of electrons is four.
• The bonding pair of the electrons is four as all the N electrons are used.

Therefore,

$\begin{array}{rcl}\mathrm{Formal}\mathrm{charge}\mathrm{of}\mathrm{N}& =& 5-4-\frac{1}{2}\times 4\\ & =& 5-4-2\\ & =& -1\end{array}$

Hence, the formal charge of N is -1.

The calculation of the formal charge for N (middle) is as follows:

• The total number of valence electrons of N is five.
• The lone pair of electrons is zero.
• The bonding pair of the electrons is eight as all the N electrons are used.

Therefore,

$\begin{array}{rcl}\mathrm{Formal}\mathrm{charge}\mathrm{of}\mathrm{N}& =& 5-0-\frac{1}{2}\times 8\\ & =& 5-0-4\\ & =& 1\end{array}$

Hence, the formal charge of N is +1.

The calculation of the formal charge for N (extreme right) is as follows:

• The total number of valence electrons of N is five.
• The lone pair of electrons is four.
• The bonding pair of the electrons is four as all the N electrons are used.

Therefore,

$\begin{array}{rcl}\mathrm{Formal}\mathrm{charge}\mathrm{of}\mathrm{N}& =& 5-4-\frac{1}{2}\times 4\\ & =& 5-4-2\\ & =& -1\end{array}$

Hence, the formal charge of N is -1.

c. The calculation of the formal charge for O is as follows:

• The total valence electrons of O are six.
• The lone pair of electrons is two.
• The bonding pair of the electrons is six as all the O electrons are used.

Therefore,

role="math" localid="1648442107315" $\begin{array}{rcl}\mathrm{Formal}\mathrm{charge}\mathrm{of}\mathrm{O}& =& 6-2-\frac{1}{2}\times 6\\ & =& 6-2-3\\ & =& +1\end{array}$

Hence, the formal charge of O is +1.

d. The calculation of the formal charge for N is as follows:

• The total valence electrons of N are five.
• The lone pair of electrons is two.
• The bonding pair of the electrons is six as all the N electrons are used.

Therefore,

$\begin{array}{rcl}\mathrm{Formal}\mathrm{charge}\mathrm{of}\mathrm{N}& =& 5-2-\frac{1}{2}\times 6\\ & =& 5-2-5\\ & =& 0\end{array}$

Hence, the formal charge of N is zero.

The calculation of the formal charge for O is as follows:

• The total valence electrons of O are six.
• The lone pair of electrons is four.
• The bonding pair of electrons is four as all the N electrons are used.

Therefore,

role="math" localid="1648442126978" $\begin{array}{rcl}\mathrm{Formal}\mathrm{charge}\mathrm{of}\mathrm{O}& =& 6-4-\frac{1}{2}\times 4\\ & =& 6-4-2\\ & =& 0\end{array}$

Hence, the formal charge of O is zero.