jodium

Jodium, known in English as iodine, is a chemical element with the symbol I and atomic number 53. It is the heaviest stable halogen and occurs mainly in seawater and in certain minerals as iodide compounds. Industrially, jodium is obtained from kelp ash, brines, and iodide-rich sources, then purified for use in chemistry and medicine.

At room temperature jodium forms a dark violet solid that sublimes easily to violet vapor. Its melting point is 113.7 °C and its boiling point is 184.3 °C. It forms diatomic molecules (I2) and readily forms salts with metals to give iodides. It participates in halogen chemistry and in the formation of polyiodides.

Biologically, jodium is an essential micronutrient for humans and other organisms. It is required for synthesis of thyroid hormones (thyroxine, T4, and triiodothyronine, T3), which regulate development and metabolism. Inadequate intake can cause goiter and neurodevelopmental deficits; adequate iodization of salt and other sources helps prevent these conditions. Excess jodium can disrupt thyroid function in some people.

Industrial and medical uses include antiseptic solutions (povidone-iodine, Lugol's solution), disinfection, and the production of iodinated contrast agents for imaging. Radioactive isotopes such as iodine-131 are used in diagnosis and treatment of thyroid disease.

Historical note: jodium was identified in 1811 by Bernard Courtois in France from seaweed ash, and its name derives from the Greek word for violet, referencing its distinctive color.