Question

Determine the formal charge of each element in the following:

(a) \({{\rm{H}}_{\rm{3}}}{{\rm{O}}^{\rm{ + }}}\)

(b) \({\rm{SO}}_{\rm{4}}^{{\rm{2 - }}}\)

(c) \({\rm{N}}{{\rm{H}}_{\rm{3}}}\)

(d) \({\rm{O}}_{\rm{2}}^{{\rm{2 - }}}\)

(e) \({{\rm{H}}_{\rm{2}}}{{\rm{O}}_{\rm{2}}}\)

Short answer

(a) The formal charge of \({\rm{H}}\) and \({\rm{O}}\)in the compound\({{\rm{H}}_{\rm{3}}}{{\rm{O}}^{\rm{ + }}}\)is\(0\) and\({\rm{ + 1}}\) respectively.

(b) The formal charge of \({\rm{S}}\)and\({\rm{O}}\)in the compound \({\rm{SO}}_{\rm{4}}^{{\rm{2 - }}}\) is \({\rm{ + 2}}\) and\({\rm{ - 1}}\)respectively.

(c) The formal charge of \({\rm{N}}\) and \({\rm{H}}\) in the compound \({\rm{N}}{{\rm{H}}_{\rm{3}}}\) is \(0\).

(d) The formal charge of\({\rm{O}}\) in the compound\({\rm{O}}_{\rm{2}}^{{\rm{2 - }}}\) is \({\rm{ - 1}}\).

(e) The formal charge of \({\rm{H}}\)and \({\rm{O}}\) in the compound \({{\rm{H}}_{\rm{2}}}{{\rm{O}}_{\rm{2}}}\) is \(0\).

Step-by-step solution

Concept Introduction

A formal charge is attributed to an atom/molecule in the covalent bonding, assuming that electrons in all chemical bonds are shared equally among atoms, irrespective of relative electronegativity.

Formal Charge of Hydronium

(a)

To find the Formal charge use the formula –

Formal Charge\({\rm{ = }}\) \({\rm{(}}\)Number of valence electrons on atom) \({\rm{ - }}\) (non-bonded electrons \({\rm{ + }}\) Bonding electrons\({\rm{)}}\).

Formal Charge for \({\rm{H}}\) is:

\(\begin{aligned}&= \left( {\rm{1}} \right){\rm{ - }}\left( {{\rm{0 + 1}}} \right)\\&= 0\end{aligned}\)

Formal Charge for \({\rm{O}}\) is:

\(\begin{aligned}&= \left( 6 \right){\rm{ - }}\left( {{\rm{2 + 3}}} \right)\\&= +1\end{aligned}\)

The formal charge for \({{\rm{H}}_{\rm{3}}}{{\rm{O}}^{\rm{ + }}}\) is found below –

Element	Bonding Electrons	Non-bonded Electrons	Valence Electrons	Formal Charge
\({\rm{H}}\)	\(1\)	\(0\)	\(1\)	\(0\)
\({\rm{O}}\)	\(3\)	\(2\)	\(6\)	\({\rm{ + 1}}\)

Therefore, the formal charge for \({\rm{H}}\) and \({\rm{O}}\) is \(0\) and \({\rm{ + 1}}\) respectively.

Formal Charge of Sulphate

(b)

To find the Formal charge use the formula –

Formal Charge \({\rm{ = }}\) \({\rm{(}}\)Number of valence electrons on atom)\({\rm{ - }}\) (non-bonded electrons\({\rm{ + }}\) Bonding electrons\({\rm{)}}\).

Formal Charge for \({\rm{S}}\)is:

\(\begin{aligned}&= \left( {\rm{6}} \right){\rm{ - }}\left( {{\rm{0 + 4}}} \right)\\&= +2\end{aligned}\)

Formal Charge for \({\rm{O}}\)is:

\(\begin{aligned}&= \left( 6 \right){\rm{ - }}\left( {{\rm{6 + 1}}} \right)\\& = -1\end{aligned}\)

The formal charge for\({\rm{SO}}_{\rm{4}}^{{\rm{2 - }}}\)is found below –

Element	Bonding Electrons	Non-bonded Electrons	Valence Electrons	Formal Charge
\({\rm{S}}\)	\(4\)	\(0\)	\(6\)	\({\rm{ + 2}}\)
\({\rm{O}}\)	\(1\)	\(6\)	\(6\)	\({\rm{ - 1}}\)

Therefore, the formal charge for\({\rm{S}}\) and\({\rm{O}}\) is \({\rm{ + 2}}\) and \({\rm{ - 1}}\) respectively.

Formal Charge of Ammonia

c)

To find the Formal charge use the formula –

Formal Charge\({\rm{ = }}\) \({\rm{(}}\)Number of valence electrons on atom)\({\rm{ - }}\)(non-bonded electrons\({\rm{ + }}\) Bonding electrons\({\rm{)}}\).

Formal Charge for \({\rm{N}}\) is:

\(\begin{aligned}&= \left( {\rm{5}} \right){\rm{ - }}\left( {{\rm{2 + 3}}} \right)\\&= 0\end{aligned}\)

Formal Charge for \({\rm{H}}\)is:

\(\begin{aligned}&= \left( 1 \right){\rm{ - }}\left( {{\rm{0 + 1}}} \right)\\&= 0\end{aligned}\)

The formal charge for \({\rm{N}}{{\rm{H}}_{\rm{3}}}\) is found below –

Element	Bonding Electrons	Non-bonded Electrons	Valence Electrons	Formal Charge
\({\rm{N}}\)	\(3\)	\(2\)	\(5\)	\(0\)
\({\rm{H}}\)	\(1\)	\(0\)	\(1\)	\(0\)

Therefore, the formal charge for \({\rm{N}}\) and \({\rm{H}}\) is \(0\).

Formal Charge of Peroxide

(d)

To find the Formal charge use the formula –

Formal Charge \({\rm{ = }}\) \({\rm{(}}\)Number of valence electrons on atom) \({\rm{ - }}\) (non-bonded electrons\({\rm{ + }}\)Bonding electrons\({\rm{)}}\).

Formal Charge for \({\rm{O}}\)is:

\(\begin{aligned}&= \left( 6 \right){\rm{ - }}\left( {{\rm{6 + 1}}} \right)\\& = -1\end{aligned}\)

The formal charge for\({\rm{O}}_{\rm{2}}^{{\rm{2 - }}}\)is found below –

Element	Bonding Electrons	Non-bonded Electrons	Valence Electrons	Formal Charge
\({\rm{O}}\)	\(1\)	\(6\)	\(6\)	\({\rm{ - 1}}\)

Therefore, the formal charge for \({\rm{O}}\) is \({\rm{ - 1}}\).

Formal Charge of Hydrogen Peroxide

(e)

To find the Formal charge use the formula –

Formal Charge\({\rm{ = }}\) \({\rm{(}}\)Number of valence electrons on atom)\({\rm{ - }}\)(non-bonded electrons\({\rm{ + }}\)Bonding electrons\({\rm{)}}\).

Formal Charge for\({\rm{H}}\)is:

\(\begin{aligned}&= \left( {\rm{1}} \right){\rm{ - }}\left( {{\rm{0 + 1}}} \right)\\&= 0\end{aligned}\)

Formal Charge for\({\rm{O}}\)is:

\(\begin{aligned}&= \left( 6 \right){\rm{ - }}\left( {{\rm{4 + 2}}} \right)\\&= 0\end{aligned}\)

The formal charge for\({{\rm{H}}_{\rm{2}}}{{\rm{O}}_{\rm{2}}}\)is found below –

Element	Bonding Electrons	Non-bonded Electrons	Valence Electrons	Formal Charge
\({\rm{H}}\)	\(1\)	\(0\)	\(1\)	\(0\)
\({\rm{O}}\)	\(2\)	\(4\)	\(6\)	\(0\)

Therefore, the formal charge for\({\rm{H}}\)and\({\rm{O}}\)is\(0\).