5 Steps to a 5 AP Chemistry

Binary Compounds

Binary compounds are compounds that consist of only two elements. Some binary com-

pounds have special names, and these special names supersede any of the rules given below.

H 2 O is water, NH 3 is ammonia, and CH 4 is methane. All other binary compounds have

a name with a suffix ide. Binary compounds may be subdivided into metal type, nonmetal

type, and acid type.

(a) Metal typeThese binary compounds begin with metals. The metal is given first in the

formula. In general, metals are the elements on the left-hand side of the periodic table,

and the nonmetals are on the right-hand side. Hydrogen, a nonmetal, is an exception

to this generalization.

First name the metal, then name the nonmetal with the suffix ide.Examples:

Formula Name

Na 2 O sodium oxide

MgCl 2 magnesium chloride

The ammonium ion (NH 4 +) is often treated as a metal, and its compounds are

named under this rule. Thus, NH 4 Cl is named ammonium chloride.

(b) Nonmetal typeThese binary compounds have formulas that begin with a nonmetal.

Prefixes are used to indicate the number of each atom present. No prefixes are used for

hydrogen. Naming the compounds can best be explained using the following examples:

Formula Name

CO carbon monoxide

SO 3 sulfur trioxide

P 4 O 10 tetraphosphorus decoxide

Carbon monoxide is one of the very few cases where the prefix mono is used.

In general, you should not use monoin any other compound.

Some of the prefixes used to denote the numbers of atoms in a compound are listed

below:

Number of atoms Prefix

1 mono

2di

3 tri

4 tetra

5 penta

6 hexa

7 hepta

8 octa

9 nona

10 deca

On many occasions the terminal aor ois dropped for oxides, so they read as

pentoxide, heptoxide, or monoxide.

In normal nomenclature, the nonmetal prefixes are not used if a metal is present.

One of the few exceptions to this is MnO 2 , sometimes called manganese dioxide.

(c) Acid type These binary compounds have formulas that begin with hydrogen.

If the compound is not in solution, the naming is similar to that of the metal type.

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