The empirical formula for aluminium selenide is AlSe.
This formula represents the simplest whole number ratio of the elements in the compound. Aluminium (Al) has a valency of +3, while selenium (Se) typically has a valency of -2. In order to balance the charges for a neutral compound, we require two aluminium ions to balance three selenide ions. Thus, the overall formula derived from these ratios is simplified to AlSe, which indicates one aluminium atom for every one selenium atom in the compound.