Iodine CAS number: 12190-71-5 Iodide (I21-) (8CI,9CI)

Violet solid with a sharp, characteristic odor.
Iodine,I, is a nonmetallic element with an orthorhombic crystal structure, a violet to black color. This poisonous element sublimes readily and is easily purified in this manner. It is insoluble in water,but is soluble in common solvents such as alcohol, ether,and carbon tetrachloride. Iodine is used as a germicide, an antiseptic, in dyes,tinctures, and pharmaceuticals. It is also used in the production of vanadium metal in the McKechnie-Seybolt process, which is the reduction of vanadium pentoxide in the presence of iodine. Iodine is used in a similar manner in the production of high-purity zirconium.For many years, iodine tincture(3% to 7% dissolved in ethyl alcohol) has been an important antiseptic. The commercial tinctures also usually contain 5% potassium iodide to provide stability. This form produces a mild burning of the skin and stains both skin and fabrics. A milder preparation is available in which about 2% iodine is contained in an oil-water emulsion which also contains lecithin.
Heavy, grayish-black plates or granules having a metallic luster; characteristic odor. Readily sublimed having a violet vapor.Soluble in alcohol, carbon disulfide, chloroform, ether, carbon tetrachloride, glycerol, and alkaline iodide solutions; insoluble
Iodine was first discovered by Barnard Courtois, a French chemist in 1811 while extracting potassium and sodium from seaweed ash. When he accidentally added sulfuric acid, a violet colored cloud evolved from the mass. The resulting gas was condensed into dark crystals-the first occurrence of observed solid iodine.Courtois analyzed them and then gave some of them to a fellow chemist, Joseph Louis Gay-Lussac, for further study.Two years later, Gay-Lussac presented his study to the scientific community, announcing the discovery of a new element that he named "iodine," after the Greek word "ioeides" meaning violet colored.A Swiss physician by the name of J.F. Coindet had previously used burnt sponge and seaweed for the treatment of goiter (an enlargement of the thyroid gland). This treatment had been in use since 3600 B.C., when it appeared in Chinese medical writings, as well as writings by the Greek physician Hippocrates. Upon hearing of the work of Courtois and Gay-Lussac, Coindet suspected that iodine might be the active ingredient in seaweed that cured goiter. In 1819, he successfully tested a tincture of iodine on 150 patients, significantly reducing the size of their goiter within one week. As a result of these early studies, in the 1830s the medical community started advocating for iodine supplements to decrease the occurrence of goiter.
A dark-violet volatile solid element belonging to the halogens (group 17 of the periodic table). It occurs in seawater and is concentrated by various marine organisms in the form of iodides. Significant deposits also occur in the form of iodates. The element is conveniently prepared by the oxidation of iodides in acid solution (using MnO2). Industrial methods similarly use oxidation of iodides or reduction of iodates to iodides by sulfur(IV) oxide (sulfur dioxide) followed by oxidation, depending on the source of the raw materials. Iodine and its compounds are used in chemical synthesis, photography, pharmaceuticals, and dyestuffs manufacture.Iodine has the lowest electronegativity of the stable halogens and consequently is the least reactive. It combines only slowly with hydrogen to form hydroiodic acid, HI. Iodine also combines directly with many electropositive elements, but does so much more slowly than does bromine or chlorine. Because of the larger size of the iodine ion and the consequent low lattice energies, the iodides are generally more soluble than related bromides or chlorides. As with the other halides, iodides of Ag(I), Cu(I), Hg(I), and Pb(II) are insoluble unless complexing ions are present.Iodine also forms a range of covalent iodides with the metalloids and non-metallic elements (this includes a vast range of organic iodides) but these are generally less thermodynamically stable and are more readily hydrolyzed than chlorine or bromine analogs.