he formula unit for the ionic compound, aluminum sulfide, consists of which of the following?

Question

? 2 Al3+ ions and 3 S2- ions
? 3 Al2+ ions and 2 S3- ions
? 3 Al+ ions and 3 S- ions
? 2 Al3+ ions and 2 S- ions
? 2 Al3- ions and 3 S2+ ions

Answer 1

The correct formula unit for aluminum sulfide is composed of aluminum ions and sulfide ions. Aluminum typically forms a \(3+\) ion (\(Al^{3+}\)), and sulfur typically forms a \(2-\) ion (\(S^{2-}\)).

To balance the charges in the compound, you need:

• 2 aluminum ions (\(Al^{3+}\)), which contribute a total charge of \(2 \times +3 = +6\)
• 3 sulfide ions (\(S^{2-}\)), which contribute a total charge of \(3 \times -2 = -6\)

Since the total positive charge from the aluminum ions equals the total negative charge from the sulfide ions, the formula unit for aluminum sulfide is \(Al_2S_3\).

Thus, the correct choice is:

• 2 Al\(^{3+}\) ions and 3 S\(^{2-}\) ions.