Calculating Formal Charge from a Lewis Structure

Calculating an atom's formal charge means subtracting its lone-pair electrons plus half its bonding electrons from its number of valence electrons.

For the central sulfur in SO2, drawn with one single bond, one double bond, and one lone pair, first name the quantities before substituting: sulfur contributes six valence electrons, two lone-pair electrons sit directly on sulfur, and six bonding electrons are shared across the single and double bonds, of which half, three bonding-pair electrons, count toward sulfur. Substituting these into the formula, formal charge equals six valence electrons minus two lone-pair electrons minus three bonding-pair electrons, all counted in electrons, giving six minus two minus three, or +1. A result of +1 is a small whole-number charge, the physically sensible size for a central atom in a stable, mostly-neutral molecule, not a large or fractional value that would flag an arithmetic slip.