When elements from the far left of the periodic table (metals) react, they tend to loose electrons to form positive ions or cations. When elements from the right react with metals, they gobble up these electrons to form negative ions, or anions. Compounds formed between metals and nonmetals where this takes place are called ionic compounds and they are named from the ions that compose them.

Cations formed from metals have the same name as the metal. If the metal can form more than one different positive ion, the charge state of the metal is put in roman numerals within parenthesis following the metal name. Sometimes an older naming scheme is used: when only two ions can be formed from a given metal, an -ous ending is given to the Latin name of the metal for the lower charged (less positive) ion and and -ic ending is given for the higher charged ion. Cations formed from non-metals are given an -ium ending.

 

Monoatomic anions are named by shortening the name of the element ad adding an -ide ending. Some simple polyatomic anions are also given the -ide ending (like hydroxide). Many polyatomic anions contain oxygen and these are called oxyanions. Usually, these anions come in groups that have the same charge but different numbers of oxygen atoms. The names of these species have the root derived from the non-oxygen atom, and the most common ion is given the -ate ending. Names for the ion with more and fewer oxygen atoms are given different suffixes and sometimes prefixes.

 

Oxyanaions that can combine with hydrogen ions (H+), are given the prefix hydrogen or dihydrogen, or in the older literature the prefix bi-. Knowing how to name compounds is important so that when we refer to specific compounds, we don't need to say "that one" or "this one" but we can call them by name.

 

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Topic 3