Symbol

I

Atomic Number

53

Atomic Mass

126.9045

Family

Group 17 (Viia) Halogen Pronunciation

EYE-uh-dine

Overview

Iodine is the heaviest of the commonly occurring halogens. The halogens are in Group 17 (VIIA) of the periodic table. The periodic table is a chart that shows how chemical elements are related to each other. Iodine's chemical properties are similar to the lighter halogens above it, fluorine, chlorine, and bromine. But its physical appearance is very different. It is a steel-gray solid that changes into beautiful purple vapors when heated.

Iodine was discovered in 1811 by French chemist Bernard Courtois (1777-1838). The element occurs primarily in seawater and in solids formed when seawater evaporates. Its single most important property may be the ability to kill germs. It is used in antiseptics, germicides (products that kill germs), and other medical applications. However, it has a great many other less common, but important, commercial applications.

Discovery and Naming