IODiin

Iodine is a chemical element with the symbol I and atomic number 53. It is a halogen and occurs as a dark violet-black solid at room temperature that readily sublimes to a violet gas. In nature it primarily forms diatomic molecules (I2) and forms a range of iodide compounds with metals and organic groups. The English name iodine has Greek origins related to its violet color.

Iodine is a trace element in seawater and rocks, and is concentrated commercially from brines and kelp-based sources. It is extracted from iodide- or iodate-containing minerals, then purified by oxidation and distillation to yield elemental iodine. The element has many radioisotopes; the most useful in medicine are 123I and 131I, while 129I is long-lived.

Iodine plays a critical biological role as a constituent of thyroid hormones, thyroxine (T4) and triiodothyronine (T3). It is required in the diet; deficiency can cause goiter and developmental disorders. Common dietary sources include seafood and iodized salt. The recommended daily intake varies by age and physiology.

Applications include antiseptics such as povidone-iodine, diagnostic imaging using iodinated contrast media, and nuclear medicine therapy with radioactive iodine for thyroid conditions. Safety concerns include thyroid disruption at improper doses, skin or mucous membrane irritation, and environmental concerns regarding radioactive isotopes. The spelling iodiin may appear in some texts as a variant of iodine, but the standard English name is iodine.