Page 102 - Theory and Problems of BEGINNING CHEMISTRY

CHAP. 6] INORGANIC NOMENCLATURE 91

EXAMPLE 6.10. What is the charge on (a) the sulfide ion, (b) the nitride ion, and (c) the fluoride ion?
Ans. (a) Sulfur is in group VI (16), and so the charge is 6 − 8 =−2 (or 16 − 18 =−2).
(b) Nitrogen is in group V (15), and so the charge is 5 − 8 =−3.
(c) Fluorine is in group VII (17), and so the charge is 7 − 8 =−1.

Oxyanions
Oxyanions consist of an atom of an element plus some number of atoms of oxygen covalently bonded to
it. The name of the anion is given by the name of the element with its ending changed to either -ate or -ite.In
some cases, it is also necessary to add the prefix per-or hypo- to distinguish all the possible oxyanions from one
another. For example, there are four oxyanions of chlorine, which are named as follows:
−
ClO 4 perchlorate ion
−
ClO 3 chlorate ion
−
ClO 2 chlorite ion
ClO − hypochlorite ion
One may think of the -ite ending as meaning “one fewer oxygen atom.” The per- and hypo- prefixes then mean
“one more oxygen atom” and “still one fewer oxygen atom,” respectively. Thus, perchlorate means one more
oxygen atom than chlorate has. Hypochlorite means still one fewer oxygen atom than chlorite has. Note that
all four oxyanions have the same central atom (Cl) and the same charge (1−). The only difference in their
constitutions is the number of oxygen atoms.
Other elements have similar sets of oxyanions, but not all have four different oxyanions. You should learn the
names of the seven ions ending in -ate for the most common elements. These are the most important oxyanions.
Use the rules given above for remembering the others. These ions are all presented in Table 6-5. Note that the
ones with central atoms in odd periodic groups have odd charges and that those in even periodic groups have
even charges.

Table 6-5 Common Oxyanions

ClO − Hypochlorite ClO 2 − Chlorite ClO 3 − Chlorate ClO 4 − Perchlorate
BrO − Hypobromite BrO 2 − Bromite BrO 3 − Bromate BrO 4 − Perbromate
IO − Hypoiodite IO 2 − Iodite IO 3 − Iodate IO 4 − Periodate
− −
NO 2 Nitrite NO 3 Nitrate
3− 3− 3−
PO 2 Hypophosphite PO 3 Phosphite PO 4 Phosphate
2− 2−
SO 3 Sulfite SO 4 Sulfate
2−
CO 3 Carbonate
Note that not all the possible oxyanions of these elements exist. If the name and formula are not given in
Table 6-5, the ion is not known. If you learn the seven ions that end in -ate plus the meaning of the ending -ite
and the prefixes, you will be able to write formulas for 20 oxyanions. You may double this number of names by
learning an additional rule in Sec. 6.4. Note from Table 6-5 that for each central element, all the ions present
have the same charge.

−
−
EXAMPLE 6.11. Name the following ions without consulting Table 6-5: (a)PO 3 ,(b) ClO 4 , and (c)IO .
3−
Ans. (a) Remembering that phosphate is PO 4 , we note that this ion has one fewer oxygen atom. It is the phosphite
3−
ion. (b) Remembering that chlorate is ClO 3 , we note that this ion has one more oxygen atom. This ion is the
−
perchlorate ion. (c) Remembering that iodate is IO 3 , we note that this ion has two fewer oxygen atoms. It is the
−
hypoiodite ion.