View source for Iodine

== Introduction ==
Iodine is a [[Chemical element|chemical element]] with the symbol I and atomic number 53. It is a member of the [[Halogens|halogen]] group that can be found in various states of matter such as solid, liquid, and gas. Iodine and its compounds are primarily used in nutrition, and industrially in the production of acetic acid and certain polymers.

== Characteristics ==
Iodine is a dark-gray/purple-black, lustrous, solid element at standard conditions that sublimes readily to form a violet gas. Its properties are mostly intermediate between those of [[Chlorine|chlorine]] and [[Bromine|bromine]]. It is less reactive than the other halogens, which include fluorine, chlorine, and bromine. Iodine exhibits significant nonmetallic character and is a relatively good insulator and a weak conductor of electricity.

== History ==
Iodine was discovered by French chemist [[Bernard Courtois]] in 1811. He was extracting sodium and potassium compounds from seaweed ash, and once these were removed, he added sulfuric acid to further process the ash. He observed a violet vapor that crystallized on cold surfaces, which he subsequently identified as a new element.

== Occurrence and Production ==
Iodine is the heaviest essential element utilized widely by life in biological functions. It is primarily obtained from seawater, oil well brines, and nitrate deposits. The world's largest iodine producers are Chile and Japan, where it is obtained from iodate solutions found in natural gas fields and brine water.

== Applications ==
The largest use of iodine is in the production of [[Acetic acid|acetic acid]]. It is also widely used in medical treatments and industrial processes. Iodine is used as a test for starch and to make solutions for antiseptics. In medicine, radioactive isotopes of iodine can be used to treat thyroid cancer.

== Biological Role and Health Effects ==
Iodine is an essential trace element; the thyroid hormones thyroxine and triiodothyronine contain iodine. In areas where there is little iodine in the diet, typically remote inland areas where no marine foods are eaten, iodine deficiency gives rise to goiter, and in severe cases can lead to cretinism in children, which is a disorder of severely stunted physical and mental growth.

== Environmental Impact ==
Iodine plays a crucial role in the environment as it cycles between the atmosphere, lithosphere, and hydrosphere in various forms. It is both a primary nutrient and a significant pollutant, particularly in the form of iodine-131, a radioactive isotope.

== See Also ==
* [[Halogens]]
* [[Chemical element]]
* [[Bernard Courtois]]
* [[Acetic acid]]
* [[Thyroid cancer]]

[[Category:Chemical elements]]
[[Category:Halogens]]
[[Category:Essential trace elements]]

[[Image:Detail-71771.jpg|thumb|center|A close-up image of iodine crystals. The crystals should be dark-gray/purple-black and lustrous. The image should be taken in a controlled environment, such as a laboratory.|class=only_on_mobile]]
[[Image:Detail-71772.jpg|thumb|center|A close-up image of iodine crystals. The crystals should be dark-gray/purple-black and lustrous. The image should be taken in a controlled environment, such as a laboratory.|class=only_on_desktop]]