Nomenclature - Fundamentals of Chemistry - page 177

classical group number minus 8, and the charge on each
third-through fifth-period oxoanion is equal to the classi-
cal group number minus 8, just as for the monatomic an-
ions. The names of most familiar oxoanions end in - ate or
- ite, depending on the relative number of oxygen atoms
per ion. Ions with more oxygen atoms than those whose
names end in - ate have the prefix per - added to the name;
ions with fewer oxygen atoms than those whose names
end in - ite have the prefix hypo - added to the name.
Names of other anions must be learned based on periodic
table relationships or individually.
A Roman numeral in parentheses in the name of the
compound designates the charge on a cation and an Arabic
numeral as a subscript in the formula designates the num-
ber of atoms or ions. The charges enable us to deduce the
numbers of ions, and vice versa, but the Roman numerals
and the Arabic numerals do not represent the same quanti-
ties. (Section 6.2)

Acids can be recognized by the fact that the ionizable
hydrogen atoms are written first in their formulas. The word
“hydrogen” does not appear in their names; the word “acid”
implies the presence of the hydrogen. Name oxoacids like
the corresponding oxoanions, with the ending - ate changed
to - ic acid or the ending - ite changed to - ous acid . Names of
binary acids have the ending - ide of the corresponding
anion changed to - ic acid and the prefix hydro - added. For
example, is chloride; is hydrochloric acid.
Name acid salts as ionic compounds, but put the
word “hydrogen” in the name of the anion (perhaps with
a prefix) to indicate that at least one ionizable hydrogen
atom is still present. For example,

Cl HCl

NaHCO 3 is sodium

hydrogen carbonate. (Section 6.3)
Name hydrates with a prefix from Table 6.1 before
the word “hydrate,” to indicate the number of water mol-
ecules. For example, CuSO 4 # 5H 2 O

is named copper(II)

sulfate pentahydrate. (Section 6.4)

Items for Special Attention

The following list summarizes the types of compounds and
ions we have learned to name in this chapter:
Binary nonmetal-nonmetal compounds
Ionic compounds
Cations
Monatomic cations
Variable charge
Constant charge
Polyatomic cations
Anions
Monatomic anions
Oxoanions
Special anions
Acids
Acid salts
Hydrates

All monatomic anions have names ending in - ide, but not
all anions with names ending in - ide are monatomic. Hy-
droxide ion, and cyanide ion, are important
examples of diatomic ions with names ending in - ide .

■ ■

OH , CN ,

Parentheses are used when two or more polyatomic ions
are present in a given formula, as in The sub-
script after the parentheses indicates the number of these
ions present. In certain cases, the parentheses also distin-
guish between familiar ions, such as the

■

Mg(ClO) 2 .

ClO ions in

ClO 2 Mg(ClO) 2 and the ion in KClO 2 .

That hydrogen is present in an acid is implied in the name
by the word “acid,” not by the word “hydrogen”. For ex-
ample, is hydrochloric acid . The word “hydrogen” is
used in names of acid salts, such as sodium hydrogen car-
bonate,

■

HCl

NaHCO 3 .

In naming the binary compounds of hydrogen in which
hydrogen is written first in the formula, name the com-
pound as if hydrogen were an alkali metal (despite the fact
that it is not, and that the compound is covalent). For ex-
ample, is named hydrogen chloride and is named
hydrogen sulfide. [These compounds do form ions to a
greater or lesser extent when they are dissolved in water.
(Section 8.4)]

■

The prefixes in Table 6.1 are used only for naming binary
nonmetal-nonmetal compounds, acid salts, and hydrates.

■

It is critical to specify the charges in formulas for ions and to
include the word “ion” if the name without that word means
something else, such as sodium ion or hydrogen sulfide ion.

■

HCl H 2 S

Roman numerals in names stand for charges, and sub-
scripts in formulas represent numbers of atoms.

■

Answers to Snapshot Reviews

6.3 A. (a) Phosphorous acid (b) Hypochlorous acid

6.1 A. (a) Dichlorine monoxide (b) Silicon tetrafluoride

(c) Nitrous acid
B. (a) (b)
6.4 A. Barium iodide dihydrate
B. CrPO 4 # 2H 2 O

B. (a) (b)
6.2 A. (a) Calcium chloride

IF 5 P 2 S 3

H 2 SO 4 NaH 2 PO 3

(b) Nickel(II) chloride

(c) Ammonium sulfite
B. (a) Pb(ClO) 2 (b) Mg 3 N 2 (c) AlPO 3