The chemical formaula for ammonium sulfide would be ammonium (NH₄⁺) plus sulfur (S⁺²). So now what we would do is figure out how to balance the charges (to create a stable molecule) using our knowledge of valence electrons. Or we can use a shortcut and switch the subscripts of the two atoms so it looks like this: (NH₄)₂S.
(We used a shortcut, but essentially what we did was figure out how many of each atom/ion we would need to create a balanced molecule.)
