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Unit 1
Elements of Chemical Structure and Inorganic Nomenclature

1-11. NAMING BINARY AND TERNARY ACIDS

All acids have hydrogen as the only cation. Binary acids are those acids that are composed of only two elements; that is, they consist of hydrogen in combination with some elemental anion.  Usually the anion is a halide (F, Cl, Br, I), but binary acids with other anions also occur.

  • The names for the binary acids are formed by using the prefix hydro-, the root name for the anion, and the suffix -ic, followed by the word acid. For example, HCl is called hydrochloric acid.
  • An exception to this rule is hydrocyanic acid which has the formula HCN. Although this is a ternary acid, the cyanide radical (CN-1) is usually treated like a halide ion when naming its compounds.
  • The binary acids are really covalent compounds which act as acids only when they are in solution, especially in water. When you know that one of the binary acids is by itself, you can properly name it in a similar manner to the salts; thus, HCl as a pure gas would be called hydrogen chloride.

Examples

  • HBr is hydrobromic acid
  • HI is hydriodic acid
  • H2S is hydrosulfuric acid
  • HF gas is called hydrogen fluoride

The ternary acids generally are made of hydrogen ion combined with one of the radicals that contain oxygen. F or this reason, they are often referred to as "oxyacids."

When naming the ternary acids, the suffixes on the names of the radicals are changed and followed by the word "acid" to show the presence of the hydrogen. Radicals ending in -ate change their suffix to -ic; radicals ending in -ite change their suffix to -ous. The prefixes, if there are any, are not changed. Occasionally, an extra syllable is added in the middle of the name for pronunciation purposes--these do not follow any pattern and must be learned. Here are some examples of naming ternary acids from the radicals:

RADICAL NAME OF RADICAL ACID NAME OF ACID
SO4-2 Sulfate H2SO4 Sulfuric acid
SO3-2 Sulfite H2SO3 Sulfurous acid
ClO-1 Hypochlorite HClO Hypochlorous acid

Examples