Here's how it breaks down:

* NH₄⁺: Ammonium is a positively charged ion (cation) formed from the combination of one nitrogen atom and four hydrogen atoms.

* S²⁻: Sulfide is a negatively charged ion (anion) formed from a sulfur atom.

Since ammonium has a +1 charge and sulfide has a -2 charge, two ammonium ions are needed to balance the charge of one sulfide ion, resulting in the formula (NH₄)₂S.