=== A binary ionic compound is composed of ions of two different elements - one of which is a metal, and the other a nonmetal. For example, sodium iodide, NaI, is composed of sodium ions, Na+ (elemental sodium is a metal), and iodide ions, I- (elemental iodine is a nonmetal).
Rule 1. The cation is written first in the name; the anion is written second in the name.
Rule 2. The name of the cation is the same as the (neutral) element from which it is derived (e.g., Na+ = "sodium").
Rule 3. The anion is named by adding the suffix -ide to the root of the element name (e.g., I- = "iodide").
Note: Greek prefixes are not used to indicate the number of atoms of each element in the formula unit for the compound (e.g., Na2O is named "sodium oxide" not "disodium oxide", or "disodium monoxide"). ===