Formal Charge and Alternative Lewis Structures

To calculate the formal charge on any atom in a Lewis structure, we assign electrons to the atom as follows  

All unshared (nonbonding) electrons are assigned to the atom on which they are found. 

For any bond—single, double, or triple—half of the bonding electrons are assigned to each atom in the bond. 

The formal charge of each atom is calculated by subtracting the number of electrons assigned to the atom from the number of valence electrons in the neutral atom. 

Let s practice by calculating the formal charges in the cyanide ion, CN , which has the Lewis structure 

Formal charge = valence electrons — j (bonding electrons) — nonbonding electrons [8.11] 

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