Question

For what type(s) of the compound do we use Roman numerals in the name?

Short answer

Names of the compounds which contain elements that can form more than one ion include Roman numerals within parenthesis immediately after the metal ion’s name to indicate its ionic charge or oxidation number.

Step-by-step solution

Step 1:Explanation

Names of the compounds which contain elements that can form more than one ion (such as transition elements), include Roman numerals within parenthesis immediately after the metal ion’s name to indicate its ionic charge or oxidation number.

Step 2:Example

Iron can form ${\mathbf{Fe}}^{\mathbf{2}\mathbf{+}}\mathbf{}{\mathbf{Fe}}^{\mathbf{3}\mathbf{+}}$ions.

The two compounds that iron forms with chlorine are ${\mathbf{FeCI}}_{\mathbf{2}}\mathbf{}\mathbf{}{\mathbf{FeCI}}_{\mathbf{3}}$named iron (II) chloride and iron (III) chloride respectively.