iodo

Iodo is the term used in several languages for the chemical element iodine. In the periodic table its symbol is I and its atomic number is 53. Iodine is a nonmetal and a halogen. At room temperature it appears as a dark violet-black solid that sublimates easily to a violet vapor.

Occurrence and production: Iodine occurs mainly in seawater and in certain mineral deposits. It is relatively rare in the earth's crust and is typically recovered from brines, iodide-containing minerals, or iodized seaweed products. Industrial production often involves oxidizing iodide to elemental iodine and refining it from brine concentrates or brine-derived salts.

Chemistry: Iodine forms diatomic I2 molecules. It forms iodide ions (I−) in salts such as sodium iodide (NaI) and potassium iodide (KI). In solution, iodine can form triiodide (I3−). Iodine is less reactive than chlorine or bromine but still acts as an oxidizing agent and participates in interhalogen compounds such as iodine monochloride (ICl).

Biology and health: Iodine is essential for vertebrates, required for the synthesis of thyroid hormones thyroxine (T4) and triiodothyronine (T3). Iodine deficiency can cause goiter and developmental problems; iodized salt is a widespread public health measure. Excess iodine can disrupt thyroid function or irritate tissues. Iodine has several radioactive isotopes, with 131I used in medicine and 129I as a long-lived tracer; naturally occurring stable isotope is 127I.

Uses and history: Iodine is used as a disinfectant (tincture of iodine) and in iodophors for skin antisepsis. It is employed as a contrast agent in radiography and in various organic synthesis methods as a source of iodide. Iodine was discovered in 1811 by Bernard Courtois and named from the Greek word for violet, due to the color of its vapor.