Editing Period 5 element (section)

===Iodine===
{{main|Iodine}}
'''Iodine''' is a [[chemical element]] with the symbol '''I''' and [[atomic number]] 53. The name is from [[Ancient Greek|Greek]] {{lang|grc|ἰοειδής}} ''ioeidēs'', meaning violet or purple, due to the color of elemental iodine vapor.<ref>Online Etymology Dictionary, s.v. [http://www.etymonline.com/index.php?term=iodine ''iodine'']. Retrieved 2012-02-07.</ref>

Iodine and its compounds are primarily used in [[nutrition]], and industrially in the production of [[acetic acid]] and certain polymers. Iodine's relatively high atomic number, low toxicity, and ease of attachment to organic compounds have made it a part of many [[radiocontrast|X-ray contrast]] materials in modern medicine. Iodine has only one [[stable isotope]]. A number of iodine radioisotopes are also used in medical applications.

Iodine is found on Earth mainly as the highly water-soluble iodide I<sup>−</sup>, which concentrates it in oceans and brine pools. Like the other [[halogen]]s, free iodine occurs mainly as a [[diatomic]] molecule I<sub>2</sub>, and then only momentarily after being oxidized from iodide by an oxidant like free oxygen.  In the universe and on Earth, iodine's high atomic number makes it a relatively [[Abundance of the chemical elements|rare element]]. However, its presence in ocean water has given it a role in biology (see below).