Formal charge

Formal charge is an electron-counting assignment that distributes bonding electrons equally between bonded atoms in a Lewis structure. It helps compare structures but does not measure an atom’s actual charge.

Lewis structure: A diagram showing bonds and lone electron pairs in a molecule or ion. Formal charge is calculated atom by atom from the bonds and lone pairs drawn in this representation.
Resonance: The representation of a molecule or ion by multiple Lewis structures differing in electron placement. Formal-charge patterns help compare resonance contributors without implying atoms move between structures.
Octet rule: The guideline that many main-group atoms form bonds until surrounded by eight valence electrons. Formal charge often helps select structures that satisfy octets, though the two criteria are distinct.
Partial charge: A fractional charge assigned to an atom to represent uneven electron distribution in a molecule. Partial charge reflects polarity, whereas formal charge follows equal sharing in Lewis bookkeeping.
Valence electron: An electron in an atom’s outer shell that can participate in chemical bonding. The atom’s neutral valence-electron count is the starting value in the formal-charge calculation.
Nitrate ion: The polyatomic ion NO₃⁻, with three equivalent N–O bonds in its resonance hybrid. Its Lewis contributors place a positive formal charge on nitrogen and negative charges on two oxygens.
Electronegativity: A measure of an atom’s tendency to attract shared electrons in a chemical bond. Formal charge treats bonding electrons equally, unlike electronegativity-based descriptions of electron distribution.
Atomic charge: The net electric charge associated with an atom, arising from its protons and electrons. Formal charge is a structural assignment and need not equal an atom’s physical charge.
Lone pair: A pair of valence electrons localized on one atom rather than shared in a bond. Each nonbonding electron assigned to an atom lowers its formal charge by one relative to the starting count.
Carbon monoxide: A diatomic molecule consisting of one carbon atom bonded to one oxygen atom. Its common Lewis structure assigns a negative formal charge to carbon and a positive one to oxygen.

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