BINARY COMPOUNDS OF NONMETALS

6.2. BINARY COMPOUNDS OF NONMETALS

The first compounds to be discussed will be compounds of two nonmetals. These binary compounds are named with the element to the left or below in the periodic table named first. The other element is then named, with its ending changed to -ide and a prefix added to denote the number of atoms of that element present. If there is more than one atom of the first element present, a prefix is used with the first element also. If one of the elements is to the left and the other below, the one to the left is named first unless that element is oxygen or fluorine, in which case it is named last. The same order of elements is used in writing formulas for these compounds. (The element with the lower electronegativity is usually named first; refer to Table 5-1.) The prefixes are presented in Table 6-2. The first six prefixes are the most important to memorize.

88 INORGANIC NOMENCLATURE

[ CHAP. 6

Table 6-2 Prefixes for Nonmetal-Nonmetal Compounds

Number of Number of Atoms

1 mono (or mon before names starting with a or o)

4 tetra (or tetr before names starting with a or o)

9 nona

5 penta (or pent before names starting with a or o)

10 deca

The systematic names presented for binary nonmetal-nonmetal compounds are not used for the hydrogen compounds of group III, IV, and V elements or for water. These compounds have common names which are used instead. Water and ammonia (NH 3 ) are the most important compounds in this class. See Sec. 6.4 for acid names.

EXAMPLE 6.1. Name and write the formula for a compound containing two atoms of oxygen and one atom of sulfur in each molecule.

Ans. This compound is a compound of two nonmetals. The sulfur is named first, since it lies below oxygen in the periodic table. Then the oxygen is named, with its ending changed to -ide and a prefix denoting the number of oxygen atoms

present. The name is sulfur dioxide and the formula is SO 2 . EXAMPLE 6.2. Name (a) CO and (b) CO 2 .

Ans. Both of these compounds are composed of two nonmetals. The carbon is named first, since it lies to the left of oxygen in the periodic table. Then the oxygen is named, with its ending changed to -ide and a prefix denoting the number of oxygen atoms present. (a) Carbon monoxide and (b) carbon dioxide.

EXAMPLE 6.3. Name and write formulas for (a) a compound with one sulfur atom and two fluorine atoms per molecule and (b) a compound with six fluorine atoms and one sulfur atom per molecule.

Ans.

(a) Sulfur difluoride SF 2 (b) Sulfur hexafluoride SF 6

Sulfur is named first, since it lies below and to the left of fluorine in the periodic table. (The element that is first in the name is also first in the formula.) The prefixes tell how many atoms of the second element there are in each molecule.

EXAMPLE 6.4. Name P 2 O 3 .

Ans. Phosphorus lies to the left and below oxygen in the periodic table, so it is named first. The number of atoms of the first element is specified because it is greater than one: diphosphorus trioxide.

EXAMPLE 6.5. Name a compound containing in each molecule (a) two oxygen atoms and a bromine atom and (b) one nitrogen atom and three chlorine atoms.

Ans. (a) Bromine dioxide and (b) nitrogen trichloride. In BrO 2 , O is above Br but to its left in the periodic table. In NCl 3 , N is above Cl and to its left. When this situation arises with oxygen or fluorine, that element is written last; any other such pair has the element to the left written first. That is the reason for the order of naming in BrO 2 and NCl 3 .

EXAMPLE 6.6. Name NH 3 .

Ans. Ammonia. The common name is used.