Naming Simple Cations

The monoatomic cations bear the same names of the elements with the addition of the word 'ion'. For example, Na⁺ is called the sodium ion and Ca²⁺ is called the calcium ion. What do you call a Na²⁺ ion, or a Ca⁺ ion? Well, Na²⁺ and Ca⁺ are not stable ions in solids or solutions. Therefore, whenever one mentions a sodium ion, we know that it is always Na⁺ and a calcium ion is always Ca²⁺. Some of the cations that have only one stable form are listed in Table I. Notice that if you refer to the periodic chart, with no exception, all the Group IA metals (they are called alkali metals) have a +1 charge and the Group IIA metals (alkaline earth metals) have a +2 charge. This is due to the ground-state electron configurations of these elements, a topic you will learn in the Chem 111A lectures in the near future. Other common metal cations that have only one stable oxidation state are: Al³⁺, Ga³⁺, Ni²⁺, Zn²⁺, Cd²⁺, and Ag⁺.

Some metals, especially the transition metals, can form more than one type of cation, such as Fe²⁺ and Fe³⁺ or Cu⁺ and Cu²⁺. To distinguish between these ions, there are two naming systems. The old style system has different suffixes in their names, e.g. Fe²⁺ is called the ferrous ion, Fe³⁺ is called the ferric ion and Cu⁺ is the cuprous ion, Cu²⁺ is the cupric ion. Notice that the ion with the lesser charge ends with –ous and the one with greater charges ends with –ic. The systematic naming method used today indicates the charge of the ion with a Roman numeral in parentheses (called the Stock number) immediately following the ion's name. Thus, Fe²⁺ is an iron(II) ion and Pb⁴⁺ is a lead(IV) ion. Ca²⁺ is just calcium ion, not calcium(II) ion, because calcium only has one kind of stable cation. The names of some simple cations are listed in Table II.

* Despite the +2 charges, each Hg in the Hg₂²⁺ ion only carries a charge of +1 (the oxidation number is +1). This is why it is called mercury(I) ion.