Iodine.

ETYM Greek iodes violetlike; ion a violet + eidos form: cf. French iode, iodine. The name was given from the violet color of its vapor. Related to Violet, Idyl.
A nonmetallic element belonging to the halogens; used especially in medicine and photography and in dyes; occurs naturally only in combination in small quantities (as in sea water or rocks); SYN. iodin, I, atomic number 53.
Grayish-black nonmetallic element, symbol I, atomic number 53, atomic weight 126.9044. It is a member of the halogen group. Its crystals give off, when heated, a violet vapor with an irritating odor resembling that of chlorine. It only occurs in combination with other elements. Its salts are known as iodides, which are found in sea water. As a mineral nutrient it is vital to the proper functioning of the thyroid gland, where it occurs in trace amounts as part of the hormone thyroxine. Absence of iodine from the diet leads to goiter. Iodine is used in photography, in medicine as an antiseptic, and in making dyes.
Its radioactive isotope 131I (half-life of eight days) is a dangerous fission product from nuclear explosions and from the nuclear reactors in power plants, since, if ingested, it can be taken up by the thyroid and damage it. It was discovered 1811 by French chemist B Courtois (1777–1838). + prikaži više