Facts About Iodine

Iodine is an essential element needed for life. It is best known for the vital role it plays in thyroid hormone production in humans as well as in all vertebrates. Iodine deficiency can lead to serious health problems, including goiter (enlarged thyroid gland), intellectual disability and cretinism.

As a pure element, iodine is a lustrous purple-black nonmetal that is solid under standard conditions. It sublimes (changes from a solid to a gaseous state while bypassing a liquid form) easily and gives off a purple vapor. Although it is technically a non-metal, it exhibits some metallic qualities. 

Iodine is classified as a halogen — a subset of very chemically reactive elements (Group 17 on the periodic table) that exist in the environment as compounds rather than as pure elements. The other halogens include fluorine (F), chlorine (Cl), bromine (Br) and astatine (At). The term halogen means "salt-producing." When these elements react with metals, they produce a wide variety of salts, such as calcium fluoride, sodium chloride (common table salt), silver bromide and potassium iodide.

Iodine is the least reactive of the halogens as well as the most electropositive, meaning it tends to lose electrons and form positive ions during chemical reactions. It is also the heaviest and the least abundant of the stable halogens. There are 30 known isotopes of iodine, but only one is naturally occurring (I-127). 

Iodine has several commercial applications and can be found in a variety of pharmaceuticals, disinfectants, inks and dyes, catalysts, photography chemicals and animal feed supplements. It plays a particularly prominent role in medicine. For example, iodine compounds are commonly used as sterilizing and wound-cleansing solutions and as internal contrasting agents in imaging techniques such as computed tomography (CT) scans, radiography and fluoroscopy. The radioactive isotope iodine-131 is also used to treat cancer in the thyroid glaAbout 99.6 percent of the Earth's mass is a mixture of 32 chemical elements, according to the World Iodine Association (WIA). The remaining 0.4 percent is divided among 64 elements — all of these in trace amounts. Iodine is the 61st element in terms of abundance, making it not only one of the least abundant nonmetallic elements on Earth but also one of the rarest elements needed for life.

Although iodine is not particularly abundant, it can be found in trace amounts nearly everywhere: water, soil, rocks, plants, animals and humans. Seawater is the largest reserve of iodine, holding about 34.5 million tons. But the concentrations are so low — averaging between 50 to 60 parts per billion (ppb) — that direct extraction is not feasible. Rivers contain less iodine, at approximately 5 ppb, according to Lenntech Water Treatment Solutions of Denmark. 

Most of the world's industrial iodine is obtained from brines (water strongly saturated in salt) associated with gas wells in Japan and from caliche ore mined in the Atacama Desert of northern Chile. In the United States, iodine is derived from deep well brines in northern Oklahoma.

Original Article on Scienceplaza