* Aluminum (Al) is a metal in group 3 of the periodic table. It has a +3 charge when it forms ions.
* Chlorine (Cl) is a nonmetal in group 17 of the periodic table. It has a -1 charge when it forms ions.
To form a neutral compound, the charges of the ions must balance. This means we need three chloride ions (3 x -1 = -3) to balance the +3 charge of one aluminum ion.
