Question

Question: What is the formal charge on the O atom in each of the following species that contains a multiple bond to O?

a.

b.

c.

Short answer

Answer

1. The formal charge on the oxygen atom is +1.
2. The formal charge on the oxygen atom is +1.
3. The formal charge on the oxygen atom is 0.

Step-by-step solution

Step-by-Step Solution Step 1: Formal charge

The charges are allotted to an atom in a molecule by assuming that the chemical bonds between the atoms are formed by equal distribution of electrons.

The relative electronegativities of the atoms are not taken into consideration.

Formula used to calculate formal charges 

The formula used to calculate the formal charges on the atoms is provided below:

$\mathrm{Formal}\mathrm{charge}=\mathrm{V}-\mathrm{N}-\frac{\mathrm{B}}{2}$

• V represents the total number of valence electrons of the atom.
• N represents the number of nonbonding electrons.
• B represents the number of bonding electrons.

Formal charges on the oxygen atoms

The electrons present in the atom’s valence/outermost shell are valence electrons. The number of valence electrons in an oxygen atom is six.

1. The oxygen atom in ‘a’ forms three bonds, and each bond has two electrons.

Thus, the total count of bonding electrons is six.

The oxygen atom bears a lone pair of electrons (two nonbonding electrons).

$\begin{array}{rcl}\mathrm{Formal}\mathrm{charge}\mathrm{on}\mathrm{oxygen}& =& 6-2-\frac{6}{2}\\ & =& 4-3\\ & =& 1\end{array}$

The formal charge on the given oxygen atom is +1.

b. In the case of b, the oxygen atom forms three bonds and contains a lone pair of electrons.

The total count of bonding electrons is six.

The total count of nonbonding electrons is two.

$\begin{array}{rcl}\mathrm{Formal}\mathrm{charge}\mathrm{on}\mathrm{oxygen}& =& 6-2-\frac{6}{2}\\ & =& 4-3\\ & =& 1\end{array}$

The formal charge on the given oxygen atom is +1.

c. The oxygen atom in structure c consists of two bond pairs and two lone pairs.

The total number of bonding electrons is four.

The total number of nonbonding electrons is four.

$\begin{array}{rcl}\mathrm{Formal}\mathrm{charge}\mathrm{on}\mathrm{oxygen}& =& 6-4-\frac{4}{2}\\ & =& 2-2\\ & =& 0\end{array}$

Therefore, the formal charge on the oxygen atom is zero.