Question
What do you meant by formal charge? Explain with example.
✓
Answer
The formal charge of an atom of a polyatomic molecule or ion is equal to the difference between total number of valence electrons in its melted state (i.e. free atomic state) and the number of electrons assigned to that atom in Lewis structure.
Formal charge can be calculated by following formula :
Formal charge on atom $=$
$
\left[\begin{array}{l}
\text { Total no. of } \\
\text { valence electrons } \\
\text { in free atom }
\end{array}\right]-\left[\begin{array}{l}
\text { Total no. of } \\
\text { l.p electrons }
\end{array}\right]-\frac{1}{2}\left[\begin{array}{l}
\text { Total no. of } \\
\text { b.p electrons }
\end{array}\right]
Example : $O _3$ (Ozone)
Formal charge on atom (1) $( F . C )=.6-4-\frac{1}{2}(4)=0$
Formal charge on atom $(2)=6-2-\frac{1}{2}(6)=1$
Formal charge on atom $(3)=6-6-\frac{1}{2}(2)=-1$
hence
Formal charge can be calculated by following formula :
Formal charge on atom $=$
$
\left[\begin{array}{l}
\text { Total no. of } \\
\text { valence electrons } \\
\text { in free atom }
\end{array}\right]-\left[\begin{array}{l}
\text { Total no. of } \\
\text { l.p electrons }
\end{array}\right]-\frac{1}{2}\left[\begin{array}{l}
\text { Total no. of } \\
\text { b.p electrons }
\end{array}\right]
Example : $O _3$ (Ozone)
Formal charge on atom (1) $( F . C )=.6-4-\frac{1}{2}(4)=0$
Formal charge on atom $(2)=6-2-\frac{1}{2}(6)=1$
Formal charge on atom $(3)=6-6-\frac{1}{2}(2)=-1$
hence
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