Formal Charge

Formal charge is the difference in valence electrons assigned to an isolated atom and the number of electrons assigned to that atom in a Lewis structure.

_{FC = (# valence electrons) – (# non-bonding electrons) – ½ (# bonding electrons)}

In an isolated atom:

• The number of electrons associated with that atom is essentially the number of valence electrons.

In a molecule:

• The electrons associated with the atom are:
• The nonbonding electrons
• The electrons in the bonding pair(s) between different atoms
• Since these electrons are shared to form a bond, we have to divide the electrons in a bonding pair equally between the atoms.

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