Naming Inorganic Compounds

Binary Molecular Compounds

When a pair of elements form more than one type of covalent compound, Greek prefixes are used to indicate how many of each element are in a compound. The more electronegative element is written last and its ending is changed to –ide.

Examples

(Q) How do you know which element goes first?

(A) The element that comes first in the following list "goes" first (is less electronegative).

B, Si, C, Sb, As, P, N, H, Te, Se, S, I, Br, Cl, O, F

Some of the Greek prefixes are given below:

Some additional rules

Examples

Finally, H2O, which according to the rules should be called dihydrogen monoxide is always called water, and NH3, or nitrogen trihydride, is always called ammonia.


Ionic compounds

Let’s review some of the features of ionic compounds

When we name an ionic compound, we write

(1) The name of the cation comes first followed by the name of the anion, changing the name of the anion to end in –ide for monotomic anions. The names of polyatomic anions are not altered.

Examples

(2) In those cases where the metal can form cations of differing charges the positive charge is given by a roman numeral in parentheses


Oxyanions

Oxyanions are those polyatomic anions containing oxygen. There are a large number of oxyanions, which makes it difficult to remember all of their names. Fortunately there is a set of rules that makes this task much easier. The rules for naming oxyanions and the names for the most important oxyanions are given below.

(1) The ending -ate is used for the most common oxyanion of a given element.

(2) The ending -ite is used for the oxyanion with the same charge, but one less oxygen than the -ate oxyanion.

(3) The prefix per- is used if there is an oxyanion with the same charge but one more oxygen than the -ate oxyanion, while the prefix hypo- is used if there is an oxyanion with the same charge but one less oxygen than the -ite oxyanion.


Acids

We constantly encounter acids in everyday life, from citric acid and ascorbic acid (vitamin C) to acetic acid (vinegar) and hydrochloric acid. We will consider acids in more detail in the next two chapters, but before we can do that we must be able to name common acids.

A simplistic definition of an acid is a compound that dissolves in water to release H+ ions. The most common acids are those which result when we add enough H+ ions to an oxyanion to balance its charge. The rules for naming simple acids are based on the names of the anions, they are given below.

(1) When the anion ends in -ide, change the ending to -ic and add the prefix hydro- to derive the name of the acid.

(2) When the anion ends in -ate, change the ending to -ic to derive the name of the acid.

(3) When the anion ends in -ite, change the ending to -ous to derive the name of the acid.