Formal charge

In chemistry, a formal charge (FC) on an atom in a molecule is defined as:

Related Topics:
Chemistry - Atom - Molecule

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FC = number of valence electrons of the atom - number of Lone pair electrons on this atom - half the total number of electrons participating in covalent bonds with this atom.

Related Topics:
Valence electron - Lone pair - Covalent bond

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When determining the correct Lewis structure (or predominant resonance structure) for a molecule, the structure is chosen such that the formal charge on each of the atoms is minimized.

Related Topics:
Lewis structure - Resonance structure

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Examples:

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• carbon in methane

FC = 4 - 0 - 8/2 = 0

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• Nitrogen in NO₂^-

FC = 5 - 2 - 6/2 = 0

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• double bonded oxygen in NO₂^-

FC = 6 - 4 - 4/2 = 0

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• single bonded oxygen in NO₂^-

FC = 6 - 6 - 2/2 = -1

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