How can I write the formula for sodium sulfide?

1 Answer

The formula for sodium sulfide is #Na_2S#.

Since this is an ionic compound, you must balance the charges so that overall charge of the compound is neutral.

Sodium, an alkali metal, has a tendency to lose one electron.
As a result sodium normally carries a positive one charge.

Sulfur, a nonmetal, has a tendency to gain 2 electrons.
This results in an ion with a negative 2 charge. Nonmetal ions end in "ide".

To obtain a neutral charge, you need two sodium ions, which provides you with a plus 2 charge balance the negative 2 charge of sulfur.