The name of an ionic compound consists of the cation name plus the anion name. For example, Na₂S is made of a cation sodium and an anion sulfide, hence the name is sodium sulfide. In TiO₂ the cation is titanium (IV) and the anion is oxide, hence the name is titanium (IV) oxide. Ca₃N₂ is calcium nitride, and AlBr₃ is aluminum bromide.

Why do some cations require a roman numeral? Because they have more than one oxidation state (or charge), for example, Fe²⁺ and Fe³⁺, iron (II) and iron (III) respectively.

How do I know what metals have more than one oxidation state? Metals of Group IA, Group IIA and aluminum (and some other exceptions) have only one oxidation state. The rest of metals have many oxidation states.

Where are the metals in the Periodic Table? Below the B (Boron) - Po (Polonium) staircase, in the bottom left corner of the Periodic Table.