Nowadays, there is a formula for aluminum fluoride. Aluminum is also a metal with active properties. Fluoride is a halogen element with strong properties. The two combine to form aluminum fluoride.

The valence of aluminum is often positive trivalent, and the valence of fluorine is always negative monovalent. According to the sum of the valence algebras in the compound is zero, the formula of aluminum fluoride is $AlF_ {3} $. To cover one atom of aluminum, three fluorine atoms are required to balance the valence. In this way, the formula of aluminum fluoride is obtained.