The Foundations of Chemistry

The oxoacid with the central element

in the highest oxidation state usually

contains more O atoms. Oxoacids

with their central elements in lower

oxidation states usually have fewer O

atoms.

4-12 Naming Ternary Acids and Their Salts 165

NAMING TERNARY ACIDS AND THEIR SALTS

A ternary compound consists of three elements. Ternary acids(oxoacids) are compounds
of hydrogen, oxygen, and (usually) a nonmetal. Nonmetals that exhibit more than one
oxidation state form more than one ternary acid. These ternary acids differ in the number
of oxygen atoms they contain. The suffixes “-ous” and “-ic” following the stem name of
the central element indicate lower and higher oxidation states, respectively. One common
ternary acid of each nonmetal is (somewhat arbitrarily) designated as the “-ic” acid. That
is, it is named by putting the element stem before the “-ic” suffix. The common ternary
“-ic acids” are shown in Table 4-16. It is important to learn the names and formulas of
these acids, because the names of all other ternary acids and salts are derived from them.
There are no common “-ic” ternary acids for the omitted nonmetals.
Acids containing one fewer oxygen atomper central atom are named in the same way
except that the “-ic” suffix is changed to “-ous.” The oxidation number of the central
element is lower by 2in the “-ous” acid than in the “-ic” acid.

4-12

Formula Ox. No. Name Formula Ox. No. Name

H 2 SO 3 
 4 sulfurousacid H 2 SO 4 
 6 sulfuricacid

HNO 2 
 3 nitrousacid HNO 3 
 5 nitricacid

H 2 SeO 3 
 4 selenousacid H 2 SeO 4 
 6 selenicacid

HBrO 2 
 3 bromousacid HBrO 3 
 5 bromicacid

TABLE 4-16 Formulas of Some “-ic” Acids

Periodic Group of Central Elements

IIA IVA VA VIA VIIA

H 3 BO 3 H 2 CO 3 HNO 3
boric acid carbonic acid nitric acid

H 4 SiO 4 H 3 PO 4 H 2 SO 4 HClO 3

silicic acid phosphoric acid sulfuric acid chloric acid

H 3 AsO 4 H 2 SeO 4 HBrO 3

arsenic acid selenic acid bromic acid

H 6 Te O 6 HIO 3

telluric acid iodic acid

Note that the oxidation state of the central atom is equal to its periodic group number, except for the halogens.

 3 
 4 
 5

 5 
 6 
 5

 5

 5

 6

 6

 5

 4