Dealing with multiple oxidation states

When the metal involved is a transition metal with more than one oxidation state  there can be more than one way to correctly name the compound, based on how you name the metal.

For example, suppose that you want to name the compound formed between the Fe³⁺ cation and the cyanide ion, CN^–. The preferred method is to use the metal name followed in parentheses by the ionic charge written as a roman numeral: iron (III). But an older naming method, which is still sometimes used (so it’s a good idea to know it), is to use -ous and -ic endings.

The ion with the lower oxidation state (lower numerical charge, ignoring the + or –) gets an -ous ending, and the ion with the higher oxidation state (higher numerical charge) gets an -ic ending. So because Fe³⁺ has a higher oxidation state than Fe²⁺, it’s called a ferric ion.

After you write the name of the metal, name the nonmetal. So the compound Fe(CN)₃ can be named

Fe(CN)₃: iron(III) cyanide, or ferric cyanide