ion
The name of a monatomic cation is simply the name of the element followed by the word ion. Thus, Na+ is the sodium ion, Al3+ is the aluminum ion, Ca2+ is the calcium ion, and so forth. We have seen that some elements lose different numbers of electrons, producing ions of different charges Figure 3.3 "Predicting Ionic Charges" . Iron, for example, can form two cations, each of which, when combined with the same anion, makes a different compound with unique physical and chemical properties. Thus, we need a different name for each iron ion to distinguish Fe2+ from Fe3+. The same issue arises for other ions with more than one possible charge. There are two ways to make this distinction. In the simpler, more modern approach, called the Stock system, an ions positive charge is indicated by a roman numeral in parentheses after the element name, followed by the word ion. Thus, Fe2+ is called the iron II ion, while Fe3+ is called the iron III ion. This system is used only for elements that form more than one common positive ion. We do not call the Na+ ion the sodium I ion because I is unnecessary. Sodium forms only a 1+ ion, so there is no ambiguity about the name sodium ion. The second system, called the common system, is not conventional but is still prevalent and used in the health sciences. This system recognizes that many metals have two common cations. The common system uses two suffixes -ic and -ous that are appended to the stem of the element name. The -ic suffix represents the greater of the two cation charges, and the -ous suffix represents the lower one. In many cases, the stem of the element name comes from the Latin name of the element. Table 3.2 "The Common System of Cation Names" lists the elements that use the common system, along with their respective cation names. Table 3.2 The Common System of Cation Names.