The Foundations of Chemistry

NAMING BINARY COMPOUNDS

Binary compounds consist of two elements; they may be either ionic or molecular. The

rule is to name the more metallic element first and the less metallic element second. The

less metallic element is named by adding an “-ide” suffix to the element’s unambiguous

stem. Stems for the nonmetals follow.

4-11

The stem for each element is derived
from the name of the element.

162 CHAPTER 4: Some Types of Chemical Reactions

IIIA IVA VA VIA VIIA

H hydr

B bor C carb N nitr O ox F fluor

Si silic P phosph S sulf Cl chlor

As arsen Se selen Br brom

Sb antimon Te tellur I iod

Formula Name Formula Name

KBr potassium bromide Rb 2 S rubidium sulfide

CaCl 2 calcium chloride Ba 3 N 2 barium nitride

NaH sodium hydride SrO strontium oxide

Binary ionic compoundscontain metal cations and nonmetal anions. The cation is

named first and the anion second.

The preceding method is sufficient for naming binary ionic compounds containing

metals that exhibit only one oxidation numberother than zero (Section 4-4). Most transi-

tion metals and the metals of Groups IIIA (except Al), IVA, and VA, exhibit more than

one oxidation number. These metals may form two or more binary compounds with the

same nonmetal. To distinguish among all the possibilities, the oxidation number of the

metal is indicated by a Roman numeral in parentheses following its name. This method

can be applied to any binary compound of a metal and a nonmetal.

The advantage of the IUPAC system is that if you know the formula you can write the

exact and unambiguous name; if you are given the name you can write the formula at

once. An older method, still in use but not recommended by the IUPAC, uses “-ous” and

“-ic” suffixes to indicate lower and higher oxidation numbers, respectively. This system

can distinguish between only two different oxidation numbers for a metal. It is therefore

not as useful as the Roman numeral system.

Ox. No. Ox. No.

Formula of Metal Name Formula of Metal Name

Cu 2 O 
 1 copper(I) oxide SnCl 2 
 2 tin(II) chloride

CuF 2 
 2 copper(II) fluoride SnCl 4 
 4 tin(IV) chloride

FeS 
 2 iron(II) sulfide PbO 
 2 lead(II) oxide

Fe 2 O 3 
 3 iron(III) oxide PbO 2 
 4 lead(lV) oxide

Familiarity with the older system is
still necessary. It is still widely used
in many scientific, engineering, and
medical fields.

Roman numerals are notnecessary for
metals that commonly exhibit only one
oxidation number in their compounds.