Question 51 E - Chemistry (OpenStax)

Question

Determine the formal charge of each element in the following: 

(a) \({\rm{HCl}}\) 

(b) \({\rm{C}}{{\rm{F}}_{\rm{4}}}\) 

(c) \({\rm{PC}}{{\rm{l}}_{\rm{3}}}\) 

(d) \({\rm{P}}{{\rm{F}}_{\rm{5}}}\)

Step-by-Step Solution

Answer

(a) The formal charge of \({\rm{H}}\) and \({\rm{Cl}}\) in the compound \({\rm{HCl}}\) is \(0\).

(b) The formal charge of \({\rm{C}}\)and \({\rm{F}}\) in the compound \({\rm{C}}{{\rm{F}}_{\rm{4}}}\) is \(0\).

(c) The formal charge of \({\rm{P}}\) and \({\rm{Cl}}\) in the compound \({\rm{PC}}{{\rm{l}}_{\rm{3}}}\) is \(0\).

(d) The formal charge of \({\rm{P}}\)and \({\rm{F}}\) in the compound \({\rm{P}}{{\rm{F}}_{\rm{5}}}\) is \(0\).

Step 1: Concept Introduction

A formal charge (\({\rm{F}}{\rm{.C}}{\rm{.}}\) or \({\rm{q}}\)) is the charge attributed to an atom in a molecule in the covalent perspective of bonding, assuming that electrons in all chemical bonds are shared equally among atoms, regardless of relative electronegativity.

Step 2: Formal Charge of Hydrogen Chloride

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 \({\rm{Cl}}\) is:

 \(\begin{aligned}&= \left( 7 \right){\rm{ - }}\left( {{\rm{6 + 1}}} \right)\\&= 0 \end{aligned}\)

The formal charge for \({\rm{HCl}}\) is found below –

Element	Bonding Electrons	Non-bonded Electrons	Valence Electrons	Formal Charge
\({\rm{H}}\)	\(1\)	\(0\)	\(1\)	\(0\)
\({\rm{Cl}}\)	\(1\)	\(6\)	\(7\)	\(0\)

 

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

Step 3: Formal Charge of Carbon Tetrafluoride

(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 \({\rm{C}}\) is: 

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

Formal Charge for \({\rm{F}}\) is: 

\(\begin{aligned}&= \left( 7 \right){\rm{ - }}\left( {{\rm{6 + 1}}} \right)\\&= 0\end{aligned}\)

The formal charge for \({\rm{C}}{{\rm{F}}_{\rm{4}}}\) is found below –

Element	Bonding Electrons	Non-bonded Electrons	Valence Electrons	Formal Charge
\({\rm{C}}\)	\(4\)	\(0\)	\(4\)	\(0\)
\({\rm{F}}\)	\(1\)	\(6\)	\(7\)	\(0\)

 

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

 

Step 4: Formal Charge of Phosphorus Trichloride

(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 \({\rm{P}}\) is: 

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

Formal Charge for \({\rm{Cl}}\) is:

 \(\begin{aligned}&= \left( 7 \right){\rm{ - }}\left( {{\rm{6 + 1}}} \right)\\&= 0\end{aligned}\)

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

Element	Bonding Electrons	Non-bonded Electrons	Valence Electrons	Formal Charge
\({\rm{P}}\)	\(3\)	\(2\)	\(5\)	\(0\)
\({\rm{Cl}}\)	\(1\)	\(6\)	\(7\)	\(0\)

 

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

Step 5: Formal Charge of Phosphorus Pentafluoride

(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 \({\rm{P}}\) is:

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

Formal Charge for \({\rm{F}}\) is: 

\(\begin{aligned}&= \left( 7 \right){\rm{ - }}\left( {{\rm{6 + 1}}} \right)\\&= 0\end{aligned}\)

The formal charge for \({\rm{P}}{{\rm{F}}_{\rm{5}}}\) is found below –

Element	Bonding Electrons	Non-bonded Electrons	Valence Electrons	Formal Charge
\({\rm{P}}\)	\(5\)	\(0\)	\(5\)	\(0\)
\({\rm{F}}\)	\(1\)	\(6\)	\(7\)	\(0\)

 

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