I2

I2 denotes the diatomic molecule of the chemical element iodine, the form in which elemental iodine is most commonly encountered in laboratory and natural contexts. At room temperature I2 appears as a shiny violet-black solid that sublimes to a violet gas. Its melting point is 113.7°C and its boiling point is 184.3°C. The molecule has a single I–I bond and a molecular weight of about 253.8 g/mol.

In the gas phase and in solution, I2 participates in redox chemistry and forms polyiodide species such as I3– in the presence of iodide. The I–I bond length is about 2.66 Å. As a halogen, I2 is a moderate oxidizer and readily reacts with many organic and inorganic substrates to form iodides and related compounds.

Occurrence and production: Iodine is relatively abundant in nature, notably in seaweed and brines. Industrial iodine is extracted by oxidation of iodide from brines or caliche ores, followed by purification and crystallization. Iodine storage typically minimizes sublimation and exposure to reducing agents.

Uses: I2 is employed as a disinfectant and antiseptic, a reagent in organic synthesis (for iodination), and a common standard in iodometric titrations and starch-iodine tests. In biology and medicine, iodine and its radioisotopes are used for imaging and therapy, and I2 is a reference source for some analytical procedures.

Safety and history: Iodine vapors are irritants and iodine compounds can be toxic; exposure can affect the thyroid and respiratory system. The element was discovered in 1811 by Bernard Courtois and named from Greek eidos, meaning violet-colored.