Britannica Sources used in this answer

How is FeCl2 named using the charge of its iron ion?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Two diagrams show the three-dimensional structure of a methane molecule: panel A uses a ball-and-stick model with a central carbon atom connected to four hydrogen atoms in a tetrahedral arrangement, while panel B illustrates the bond angle of 109.5 degrees and bond length of 1.09 angstroms between carbon and hydrogen atoms. — chemical compound Methane, in which four hydrogen atoms are bound to a single carbon atom, is an example of a basic chemical compound. The structures of chemical compounds are influenced by complex factors, such as bond angles and bond length.

The chemical compound ${FeCl}_{2}$ is named iron(II) chloride because it contains the ${Fe}^{2 +}$ ion.1

In chemistry, when a metal can form more than one type of cation, the charge of the specific ion must be indicated in the compound's name using a Roman numeral in parentheses. Because iron can exist as either ${Fe}^{2 +}$ or ${Fe}^{3 +}$ , the numeral (II) is used to specify the presence of the ${Fe}^{2 +}$ ion.1

Alternatively, an older nomenclature system uses the suffix -ous for the ion with the lower charge and -ic for the ion with the higher charge. Under this system, ${FeCl}_{2}$ is referred to as ferrous chloride, while ${FeCl}_{3}$ is known as ferric chloride.12