CK-12-Chemistry Intermediate

http://www.ck12.org Chapter 7. Chemical Nomenclature

than two common oxoanions, such as chlorine:

• ClO−, hypochlorite


• ClO 2 −, chlorite


• ClO 3 −, chlorate


• ClO 4 −, perchlorate

For larger families of oxoanions, the ion with one more oxygen atom than the–ateanion is given aper-prefix, and
the ion with one fewer oxygen atom than the–iteanion is given ahypo-prefix.

Naming Ternary Ionic Compounds

As in the case of binary ionic compounds, ternary ionic compounds can be named by writing the name of the cation
followed by the name of the anion. Some examples are listed below (Table7.6):

TABLE7.6: Examples of Ternary Ionic Compounds

Formula Name

NaNO 3 sodium nitrate

NH 4 Cl ammmonium chloride

Fe(OH) 3 iron(III) hydroxide

When more than one polyatomic ion is present in a compound, the formula of the entire ion is placed in parentheses,
and a subscript outside of the parentheses indicates how many of those ions are in the compound. In the last example
above, there is one Fe^3 +cation present for every three OH−anions.

Writing Formulas for 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. 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 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.

Note that there are two polyatomic ions that produce unusual formulas. The Hg 22 +ion is called either the dimercury
ion or, preferably, the mercury(I) ion. When combined with an anion that has a 1−charge, such as chloride, the
formula is Hg 2 Cl 2. Because the cation consists of two Hg atoms bonded together, this formula isnot reduced to