Naming polyatomic ions and acids Definition Polyatomic ions are similar to monatomic ions in that they both have an ionic charge (+ or -). Polyatomic ions are made of two or more atoms that act as a unit Examples ? Naming compounds with polyatomic ions Nitrate ion NO3-1 Phosphate ion PO4-3 Sulfate ion SO4-2 Ammonium ion NH4+1 Naming polyatomic ions The name of the ion usually ends in either -ite or -ate. The -ite ending indicates a low oxidation state (NO-2 ion - nitrite ion). The -ate ending indicates a high oxidation state (NO-3 ion - nitrate ion). Naming polyatomic ions Prefixes also can be used. The prefix hypo- indicates the very lowest oxidation state. (ClO- ion - hypochlorite ion)