The Foundations of Chemistry

If you don’t already know them, you

should learn these common prefixes.

Number Prefix

2di

3 tri

4 tetra

5 penta

6 hexa

7 hepta

8 octa

9 nona

10 deca

4-11 Naming Binary Compounds 163

Some compounds contain polyatomic ions that behave much like monatomic anions.
Compounds that contain these ions are called pseudobinary ionic compounds.The
prefix “pseudo-” means “false”; these compounds are named as though they were binary
compounds. The common examples of such polyatomic anions are the hydroxide ion,
OH, and the cyanide ion, CN. The ammonium ion, NH 4
, is the common cation that
behaves like a simple metal cation.

Ox. No. Ox. No.
Formula of Metal Name Formula of Metal Name

CuCl 
 1 cuprous chloride SnF 2 
 2 stannous fluoride

CuCl 2 
 2 cupric chloride SnF 4 
 4 stannic fluoride

FeO 
 2 ferrous oxide Hg 2 Cl 2 
 1 mercurous chloride

FeBr 3 
 3 ferric bromide HgCl 2 
 2 mercuric chloride

Formula Name Formula Name

NH 4 I ammonium iodide NH 4 CN ammonium cyanide

Ca(CN) 2 calcium cyanide Cu(OH) 2 copper(II) hydroxide or cupric hydroxide
NaOH sodium hydroxide Fe(OH) 3 iron(III) hydroxide or ferric hydroxide

A list of common cations and anions appears in Table 4-15. It will enable you to name
many of the ionic compounds you encounter.
Nearly all binary molecular compoundsinvolve two nonmetalsbonded together.
Although many nonmetals can exhibit different oxidation numbers, their oxidation
numbers are notproperly indicated by Roman numerals or suffixes. Instead, elemental
proportions in binary covalent compounds are indicated by using a prefixsystem for
both elements. The Greek and Latin prefixes for one through ten are mono, di, tri, tetra,
penta, hexa, hepta, octa, nona, and deca. The prefix “mono-” is omitted for both ele-
ments except in the common name for CO, carbon monoxide. We use the minimum
number of prefixes needed to name a compound unambiguously. The final “a” in a prefix
is omitted when the nonmetal stem begins with the letter “o”; we write “heptoxide,” not
“heptaoxide.”

Formula Name Formula Name

SO 2 sulfur dioxide Cl 2 O 7 dichlorine heptoxide

SO 3 sulfur trioxide CS 2 carbon disulfide

N 2 O 4 dinitrogen tetroxide SF 4 sulfur tetrafluoride

As 4 O 6 tetraarsenic hexoxide SF 6 sulfur hexafluoride

Binary acidsare compounds in which H is bonded to a Group VIA element other
than O or to a Group VIIA element; they act as acids when dissolved in water. The pure
compounds are named as typical binary compounds.Their aqueous solutions are named by
modifying the characteristic stem of the nonmetal with the prefix “hydro-” and the suffix
“-ic” followed by the word “acid.” The stem for sulfur in this instance is “sulfur” rather
than “sulf.”