http://www.ck12.org Chapter 7. Chemical Nomenclature
The crisscross method first yields Pb 2 O 4 for the formula, but that must be reduced to PbO 2 , which is the correct
formula.
Ternary Ionic Compounds
Writing a formula for a ternary ionic compound involves the same steps as for a binary ionic compound. Write the
symbol and charge of the cation followed by the symbol and charge of the anion. Use the crisscross method to ensure
that the final formula is neutral. For example, calcium nitrate is composed of calcium cations and nitrate anions.
The charge is balanced by the presence of two nitrate ions and one calcium ion. Parentheses are used around the
nitrate ion because more than one of the polyatomic ion is needed. If only one polyatomic ion is present in a formula,
parentheses are not used. For example, the formula for calcium carbonate is CaCO 3. The carbonate ion carries a 2−
charge, so it exactly balances the 2+ charge of the calcium ion.
Lesson Summary
- Ionic compounds are composed of cations and anions, which combine in a ratio that makes the overall
compound electrically neutral. - Ionic compounds are named by writing the name of the cation followed by the name of the anion.
- Monatomic cations have the same name as their parent element, whereas monatomic anions end in -ide.
- For main group elements, the charges of monatomic cations and anions can be determined by looking at which
group the element belongs to on the periodic table.