Question 52 E - Chemistry (OpenStax)

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

Step-by-Step Solution

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 1: 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.

Step 2: 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.

Step 3: 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.

 

Step 4: 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 \(0\).

Step 5: 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 \({\rm{ - 1}}\).

Step 6: 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 \(0\).