Q54E - Chemistry (OpenStax)

Question

Question: Calculate the formal charge of each element in the following compounds and ions: 

(a) \({{\rm{F}}_{\rm{2}}}{\rm{CO}}\) 

(b) \({\rm{N}}{{\rm{O}}^{\rm{ - }}}\) 

(c) \({\rm{BF}}_{\rm{4}}^{\rm{ - }}\) 

(d) \({\rm{SnCl}}_{\rm{3}}^{\rm{ - }}\) 

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

(f) \({\rm{Cl}}{{\rm{F}}_{\rm{3}}}\) 

(g) \({\rm{Se}}{{\rm{F}}_{\rm{6}}}\) 

(h) \({\rm{PO}}_{\rm{4}}^{{\rm{3 - }}}\)

Step-by-Step Solution

Answer

1. The formal charge of \({\rm{F,C}}\) and \({\rm{O}}\) in the compound \({{\rm{F}}_{\rm{2}}}{\rm{CO}}\) is \(0\).
2. The formal charge of \({\rm{N}}\) and \({\rm{O}}\) in the compound \({\rm{N}}{{\rm{O}}^{\rm{ - }}}\) is \({\rm{ - 1}}\) and \({\rm{0}}\) respectively.
3. The formal charge of \({\rm{B}}\) and \({\rm{F}}\) in the compound \({\rm{BF}}_{\rm{4}}^{\rm{ - }}\) is \({\rm{ - 1}}\) and \({\rm{0}}\) respectively.
4. The formal charge of \({\rm{Sn}}\) and \({\rm{Cl}}\) in the compound \({\rm{SnCl}}_{\rm{3}}^{\rm{ - }}\) is \({\rm{ - 1}}\) and \({\rm{0}}\) respectively.
5. The formal charge of \({\rm{C}}\) and \({\rm{H}}\) in the compound \({{\rm{H}}_{\rm{2}}}{\rm{CC}}{{\rm{H}}_{\rm{2}}}\) is \(0\).
6. The formal charge of \({\rm{Cl}}\) and \({\rm{F}}\) in the compound \({\rm{Cl}}{{\rm{F}}_{\rm{3}}}\) is \(0\).
7. The formal charge of \({\rm{Se}}\) and \({\rm{F}}\) in the compound \({\rm{Se}}{{\rm{F}}_{\rm{6}}}\) is \(0\).
8. The formal charge of \({\rm{H}}\) and \({\rm{O}}\) in the compound \({\rm{PO}}_{\rm{4}}^{{\rm{3 - }}}\) is \({\rm{ + 1}}\) and \({\rm{ - 1}}\) respectively.

Step 1: Concept Introduction

A formal charge (\({\rm{F}}{\rm{.C}}{\rm{.}}\) or \({\rm{q}}\)) is the charge on an atom within a molecule in covalent bonding, assumes that electrons in all chemical bonds are shared equally irrespective of relative electronegativity.

Step 2: Formal Charge of Carbonyl Fluoride

(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 \(F\) is: \(\begin{array}{l}{\rm{ = }}\left(7 \right){\rm{ - }}\left({{\rm{6 + 1}}} \right)\\{\rm{ = 0}}\end{array}\)

Formal Charge for \({\rm{C}}\) is: \(\begin{array}{l}{\rm{ = }}\left( 4 \right){\rm{ - }}\left( {{\rm{0 + 4}}} \right)\\{\rm{ = 0}}\end{array}\)

Formal Charge for \({\rm{O}}\) is: \(\begin{array}{l}{\rm{ = }}\left( 6 \right){\rm{ - }}\left( {{\rm{4 + 2}}} \right)\\{\rm{ = 0}}\end{array}\)

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

Element	Bonding Electrons	Non-bonded Electrons	Valence Electrons	Formal Charge
\({\rm{F}}\)	\(1\)	\(6\)	\(7\)	\(0\)
\({\rm{C}}\)	\(4\)	\(0\)	\(4\)	\(0\)
\({\rm{O}}\)	\(2\)	\(4\)	\(6\)	\(0\)

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

Step 3: Formal Charge of Nitrosonium

(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 \({\rm{N}}\) is: \(\begin{array}{l}{\rm{ = }}\left( {\rm{5}} \right){\rm{ - }}\left( {{\rm{4 + 2}}} \right)\\{\rm{ =  - 1}}\end{array}\)

Formal Charge for \({\rm{O}}\) is: \(\begin{array}{l}{\rm{ = }}\left( 6 \right){\rm{ - }}\left( {{\rm{4 + 2}}} \right)\\{\rm{ = 0}}\end{array}\)

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

Element	Bonding Electrons	Non-bonded Electrons	Valence Electrons	Formal Charge
\({\rm{N}}\)	\(2\)	\(4\)	\(5\)	\({\rm{ - 1}}\)
\({\rm{O}}\)	\(2\)	\(4\)	\(6\)	\({\rm{0}}\)

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

Step 4: Formal Charge of Tetrafluoroborate

(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 \({\rm{B}}\) is: \(\begin{array}{l}{\rm{ = }}\left( {\rm{3}} \right){\rm{ - }}\left( {{\rm{0 + 4}}} \right)\\{\rm{ =  - 1}}\end{array}\)

Formal Charge for \({\rm{F}}\) is: \(\begin{array}{l}{\rm{ = }}\left( 7 \right){\rm{ - }}\left( {{\rm{6 + 1}}} \right)\\{\rm{ = 0}}\end{array}\)

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

Element	Bonding Electrons	Non-bonded Electrons	Valence Electrons	Formal Charge
\({\rm{B}}\)	\(4\)	\(0\)	\(3\)	\({\rm{ - 1}}\)
\({\rm{F}}\)	\(1\)	\(6\)	\(7\)	\(0\)

Therefore, the formal charge for \({\rm{B}}\) and \({\rm{F}}\) is \({\rm{ - 1}}\) and \(0\) respectively.

Step 5: Formal Charge of Tin Chloride

(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 \({\rm{Sn}}\) is: \(\begin{array}{l}{\rm{ = }}\left( {\rm{4}} \right]{\rm{ - }}\left( {{\rm{2 + 3}}} \right)\\{\rm{ =  - 1}}\end{array}\)

Formal Charge for \({\rm{Cl}}\) is: \(\begin{array}{l}{\rm{ = }}\left( 7 \right){\rm{ - }}\left( {{\rm{6 + 1}}} \right)\\{\rm{ = 0}}\end{array}\)

The formal charge for \({\rm{SnCl}}_{\rm{3}}^{\rm{ - }}\) is found below –

Element	Bonding Electrons	Non-bonded Electrons	Valence Electrons	Formal Charge
\({\rm{Sn}}\)	\(3\)	\(2\)	\(4\)	\({\rm{ - 1}}\)
\({\rm{Cl}}\)	\(1\)	\(6\)	\(7\)	\(0\)

Therefore, the formal charge for \({\rm{Sn}}\) and \({\rm{Cl}}\) is \({\rm{ - 1}}\) and \(0\) respectively.

Step 6: Formal Charge of Ethene

(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 \({\rm{C}}\) is: \(\begin{array}{l}{\rm{ = }}\left( {\rm{4}} \right){\rm{ - }}\left( {{\rm{0 + 4}}} \right)\\{\rm{ = 0}}\end{array}\)

Formal Charge for \({\rm{H}}\) is: \(\begin{array}{l}{\rm{ = }}\left( 1 \right){\rm{ - }}\left( {{\rm{0 + 1}}} \right)\\{\rm{ = 0}}\end{array}\)

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

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

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

Step 7: Formal Charge of Chlorine Trifluoride

(f)

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 \({\rm{Cl}}\) is: \(\begin{array}{l}{\rm{ = }}\left( {\rm{7}} \right){\rm{ - }}\left( {{\rm{4 + 3}}} \right)\\{\rm{ = 0}}\end{array}\)

Formal Charge for \({\rm{F}}\) is: \(\begin{array}{l}{\rm{ = }}\left( 7 \right){\rm{ - }}\left( {{\rm{6 + 1}}} \right)\\{\rm{ = 0}}\end{array}\)

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

Element	Bonding Electrons	Non-bonded Electrons	Valence Electrons	Formal Charge
\({\rm{Cl}}\)	\(3\)	\(4\)	\(7\)	\(0\)
\({\rm{F}}\)	\(1\)	\(6\)	\(7\)	\(0\)

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

Step 8: Formal Charge of Selenium Hexafluoride

(g)

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 \({\rm{Se}}\) is: \(\begin{array}{l}{\rm{ = }}\left( {\rm{6}} \right){\rm{ - }}\left( {{\rm{0 + 6}}} \right)\\{\rm{ = 0}}\end{array}\)

Formal Charge for \({\rm{F}}\) is: \(\begin{array}{l}{\rm{ = }}\left( 7 \right){\rm{ - }}\left( {{\rm{6 + 1}}} \right)\\{\rm{ = 0}}\end{array}\)

The formal charge for \({\rm{Se}}{{\rm{F}}_{\rm{6}}}\) is found below –

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

Therefore, the formal charge for \({\rm{Se}}\) and \({\rm{F}}\) is \(0\)and \({\rm{ - 1}}\) respectively.

Step 9: Formal Charge of Phosphate

(h)

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: \(\begin{array}{l}{\rm{ = }}\left( {\rm{5}} \right){\rm{ - }}\left( {{\rm{0 + 4}}} \right)\\{\rm{ = 0}}\end{array}\)

Formal Charge for \({\rm{O}}\) is: \(\begin{array}{l}{\rm{ = }}\left( 6 \right){\rm{ - }}\left( {{\rm{6 + 1}}} \right)\\{\rm{ = 0}}\end{array}\)

The formal charge for \({\rm{PO}}_{\rm{4}}^{{\rm{3 - }}}\) is found below –

Element	Bonding Electrons	Non-bonded Electrons	Valence Electrons	Formal Charge
\({\rm{P}}\)	\(4\)	\(0\)	\(5\)	\({\rm{ + 1}}\)
\({\rm{O}}\)	\(1\)	\(6\)	\(6\)	\({\rm{ - 1}}\)

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