The first step in writing formulas for ionic compounds is by writing the symbol for the metal cation and its charge followed by the symbol for the nonmetal anion and its charge. Obtain charges from the element's group number in the periodic table. If polyatomic cations or polyatomic anions are involved, then look up their formulas and charges. Next, adjust the subscript on each cation and anion to balance the overall charge. Finally, check that the sum of the charges of the cations equals the sum of the charges of the anions.
Work Step by Step
Remember that the sum of the negative and positive charges should match for a net neutral charge; You are essentially finding the smallest whole number ratio of ions that allows for this.