Rule:
1. The name of the cation (positive ion) is written first, followed by the name of the anion (negative ion).
2. The oxidation state of the cation is indicated by a Roman numeral in parentheses immediately after the cation's name.
3. If the anion is a polyatomic ion, its name ends with the suffix "-ide."
Examples:
- Iron(II) chloride (FeCl2): The iron cation has a +2 oxidation state, so it is named as "iron(II)." The anion is chloride, so the compound name becomes "iron(II) chloride."
- Copper(I) oxide (Cu2O): The copper cation has a +1 oxidation state, so it is named as "copper(I)." The anion is oxide, so the compound name becomes "copper(I) oxide."
- Chromium(III) sulfate (Cr2(SO4)3): The chromium cation has a +3 oxidation state, so it is named as "chromium(III)." The anion is sulfate, so the compound name becomes "chromium(III) sulfate."
