Many metallic elements have only one possible valence. The names for the cations formed by these metals are given the name of the element. For example, Na+1 is called sodium ion; Ca+2 is called calcium ion. Other metallic elements, however, may have more than one valence. Since valence is a measure of combining power, these elements may form more than one compound with the same anion. Therefore, we must have some way to differentiate between the varying valences when we name them. There are two common method s for doing this.
The first method uses a root word from the name of the element (or the Latin name for the element) with a suffix to indicate the valence state. The suffix --ous indicates the lower valence; the suffix -ic indicates the higher valence. For example, Hg+1 is called mercurous ion, but Hg+1 is called mercuric ion.
- Al+3 is called an aluminum ion.
- Fe+2 is called ferrous ion.
- Fe+3 is a is called a ferric ion.
- K+1 is called a potassium ion.
- Cu+1 is called a cuprous ion.
- Cu+2 is a cupric ion.
- Ba+2 is a barium ion.
The second method for naming metallic cations uses the name of the element followed by a roman numeral in parentheses to indicate the valence. For example, Cu+1 is written as copper (I) and Cu+2 is written as copper (II). Remember, these methods for specifying valence need be used only when there is more than one valence possible.
- Fe+2 is written iron (II) (ferrous).
- Fe+3 is written iron (III) (ferric).
- Mg+2 is wrtten magnesium.
- Hg+1 is written mercury (I) (mercurous).
- Ag+1 is written silver.
- Pb+4 is written lead (IV) (plumbic).