The charge an atom would have if bonding electrons were shared equally; helps pick the best Lewis structure.
Practise Bonding & Molecular Structure All Bonding & Molecular Structure topics
Formal charge is a bookkeeping value assigned to each atom in a Lewis structure, calculated as valence electrons minus non-bonding electrons minus half the bonding electrons. It assumes that bonding electrons are shared equally, so it is a tool for comparing structures rather than a measure of the true charge distribution. Among possible Lewis structures, the preferred one has formal charges close to zero, places negative charges on the most electronegative atoms and keeps like charges on adjacent atoms apart. The formal charges of all atoms always sum to the overall charge of the species.
Key ideas: Formula: FC equals valence electrons minus nonbonding electrons minus half the bonding electrons. Check with the sum equal to the species charge. Choose the structure with the smallest magnitudes, negative on the more electronegative atom. For sulfate, a structure with S=O double bonds gives zero formal charges on sulfur but needs an expanded octet.
Common mistakes and connections: Do not confuse formal charge with oxidation state or real partial charge: in CO the oxygen carries the formal plus even though it is more electronegative, and the real polarity is the opposite. Another error is forgetting to use half of the bonding electrons. Connects to resonance weighting and Lewis structure selection.
In CO the best Lewis structure is a triple bond with a lone pair on each atom, giving formal charges of -1 on carbon and +1 on oxygen even though oxygen is more electronegative. The interactive lesson shows this as a live animation or chart.
In carbon monoxide the structure with a C-O triple bond gives carbon a formal charge of -1 and oxygen +1, which is the preferred bookkeeping.
The charge an atom would have if bonding electrons were shared equally; helps pick the best Lewis structure.
Formal Charge is a intermediate topic in Bonding & Molecular Structure. It builds on the vocabulary of beginner topics in this area.
Study these earlier topics in Bonding & Molecular Structure first: Lewis Structures, Single Double and Triple Bonds, Lone Pairs.
The next topics in Bonding & Molecular Structure are Resonance and Resonance Hybrid.
Yes. The interactive lesson includes a self-check question on Formal Charge, and the Bonding & Molecular Structure quiz draws on every topic in this area.
Formal Charge is topic 11 of 104 in Bonding & Molecular Structure.