What is the chemical formula for ferric sulfide?

The chemical formula for ferric sulfide is Fe2S3. The suffix -ic in ferric indicates that the oxidation state of the iron is +3; sulfur normally has a charge of -2, so the chemical formula for ferric sulfide is Fe2S3.

There are two major oxidation states of iron: (II) and (III). Binary compounds must have a balanced charge, so the number of ions in the compound must be neutral. Because the cation has charge +3 and the anion has charge -2, the cation must have two atoms and the anion must have three atoms so that the total charge is +6 and -6, giving a net charge of zero.