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Iodine

. Iodine, symbol I, chemically reactive element, a blue-black solid at room temperature. In group 17 (or VIIa) of the periodic table , iodine is one of the halogens . Its atomic number is 53. Iodine was first isolated from seaweed residues in 1811 by Bernard Courtois, a French manufacturer of saltpeter. The discovery was confirmed and announced by the French chemists Charles Desormes and Nicholas ClĂ©ment. The nature of the element was further established in 1813 by the French chemist Joseph Louis Gay-Lussac , who also gave iodine its name. PROPERTIES AND OCCURRENCE The atomic weight of iodine is 126.905. Unlike the lighter halogens, iodine is a crystalline solid at room temperature. The lustrous, blue-black, soft substance sublimes when heated, giving off a violet vapor with a stinging odor like that of chlorine. The vapor rapidly condenses again on a cold surface. Iodine melts at 113.6° C (236° F) and boils at 185° C (365° F). The only isotope that occurs in nature is stable, but seve