1. Determine the charges of the ions:
* Potassium (K) is in Group 1 of the periodic table, so it forms a +1 ion (K⁺).
* Sulfur (S) is in Group 16 of the periodic table, so it forms a -2 ion (S²⁻).
2. Balance the charges:
To have a neutral compound, the total positive charge must equal the total negative charge. We need two potassium ions (2 x +1 = +2) to balance the charge of one sulfide ion (-2).
3. Write the formula:
The formula of the ionic compound is K₂S.
