CHEMICAL COMPOUNDS BASIC INFORMATION AND TUTORIALS

NAMES OF CHEMICAL COMPOUNDS

Ionic Compounds
Compounds with a metal and a nonmetal or with any polyatomic ion are named as ionic compounds. The name consists of the name of the positive ion, followed by that of the negative ion.

Monoatomic (one-atom) ions are named by the element from which they derive. In the case of negative ions, the suffix -ide is added to the stem of the name. The stem is the name without suffixes like -ine, -ogen, -ygen, or -ur. The ion corresponding to oxygen is the oxide ion: K2O is potassium oxide.

Many metals that are not from the main groups (and even a few that are) can take more than one charge. In these cases the charge, in the form of a Roman numeral, is added to the name of the element: Fe(NO3)2— iron(II) nitrate. Polyatomic ions (ions with more than one atom) have an irregular pattern of names.

Binary (Two-Element) Compounds of Nonmetals
The number of each atom in the formula is indicated by prefixes representing Greek numbers. Often mono- (one) is omitted. Before a vowel, the a- is omitted. The second element named gets an -ide suffix to the stem: for example, N2O5—dinitrogen pentoxide.

The number prefixes should not be used for ionic compounds, although sometimes they are in common names. Many binary compounds of nonmetals have wellestablished common names. H2O is called water, not dihydrogen oxide. NH3 is called ammonia.

number prefixes
1 mono-
2 di-
3 tri-
4 tetra-
5 penta-
6 hexa-
7 hepta-
8 octa-
9 nona-
10 deca-
11 undeca-
12 dodeca-

Acids
Compounds of hydrogen and a group 7A element have the annoying characteristic of having two names. In the absence of water, they are named as binary compounds of nonmetals. Anhydrous (no water) HCl is called hydrogen chloride.

When dissolved in water, they are named as hydroacids. They take the prefix hydro- followed by the stem of the group 7A element with an -ic acid suffix. Aqueous (in water) HCl is called hydrochloric acid.

Compounds that can be thought of as being the result of adding enough H+ ions to balance the charge on a polyatomic ion containing oxygen are called oxyacids. Oxyacids are named by changing the -ate suffix on the polyatomic ion to -ic acid. If the polyatomic ion has an -ite suffix it changes to -ous acid. NO3 − is nitrate ion; HNO3 is nitric acid.  SO3 2− is sulfite ion; H2SO3 is sulfurous acid (notice that we put the -ur suffix back on sulfur).