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How Are Multivalent Ionic Compounds Named?

Atoms are neutrally charged due to an even number of electrons and protons. The gain or loss of electrons can create negatively or positively charged atoms called ions. Ionic compounds are created when a charged atom attracts an oppositely charged atom. Ionic compounds can have only one possible charge or more than one possible charge. In the latter case, they're called multivalent ionic compounds. Learning to name multivalent ionic compounds based on their chemical formula is most easily done with an example compound, such as Cu3PO3.

Identifying the Cation
- Identify the cation based on the knowledge that metals form cations and nonmetals form anions. Cations are also written first in chemical formulas. In the example Cu3PO3, the cation is copper (Cu). Look at the periodic table to determine whether copper has more than one possible charge. Because it does, write an open parenthesis after it with the possible charges, which in this case are +1 and +2: copper (1, 2).
Identifying the Anion
- Identify the anion based on the metal/nonmetal rule but also take into account polyatomic ionic ions, which are compounds that are treated as a single unit. Put a parenthesis around the polyatomic ion in the original chemical formula: Cu3(PO3). PO3 is phosphite, which has a charge of 3 -. Rewrite the formula with the charge outside the parenthesis: Cu3(PO3)3 -.
Applying Math
- At this point, the known information is copper (1, 2) phosphite or Cu3(PO3)3 -. Multiply the anion's charge (here, 3-) by the subscript of the anion. Because the phosphite is polyatomic, the 3 subscript on the oxygen is not what gets used. The subscript would appear on the exterior of the parenthesis. Since there is nothing there, it is treated as 1 and 1 * 3 = 3. Divide this value by the subscript of the cation, copper: 3 / 3 = 1.
Name the Multivalent Ionic Compound
- Write the result of the subscript division as a Roman numeral following the cation, within parenthesis: copper (I). Follow that with the name of the anion: copper (I) phosphite. Because copper (I) is also written as cuprous, the final name could be written as cuprous phosphite.

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