Watch video 2.7.2 When you have a metal and a nonmetal, you have an ionic bond, and use the principle of charge neutrality, and use the lowest whole number ratio.
Between two nonmetals there is no charge, and you use greek prefixes to indicate how many of each is in the atom.
Between two metals, you have an alloy, and use common names, like bronze, brass. But even then, the ratios change. We are not covering that in this class.