Iodine
Iodine is a halogen element with atomic number 53 and symbol I. Its dark, lustrous solid readily sublimes into violet vapor.
Halogens: Halogens are the Group 17 elements, a family of reactive nonmetals that includes fluorine, chlorine, bromine, and iodine. Iodine is the heaviest naturally occurring stable halogen and shares the family’s seven valence electrons.
Iodide: Iodide is the negatively charged iodine ion, I⁻, formed when iodine gains one electron. Iodine commonly converts to iodide in reactions and biological fluids.
Iodine deficiency: Iodine deficiency is inadequate iodine intake that limits thyroid hormone production and can impair growth and development. Dietary iodine prevents deficiency disorders, including goiter and developmental harm.
Bernard Courtois: Bernard Courtois was a French chemist who discovered iodine in 1811 while processing seaweed ash. His observation of violet vapors began iodine’s identification as a new element.
Bromine: Bromine is the halogen element with atomic number 35 and symbol Br; it is a volatile reddish-brown liquid at room temperature. Bromine is the only other halogen liquid near room temperature, unlike solid iodine.
Atomic number: Atomic number is the number of protons in an atom’s nucleus and defines the chemical element. Iodine’s atomic number, 53, fixes its identity and nuclear charge.
Iodine–starch test: The iodine–starch test is a color reaction in which iodine species produce a deep blue-black complex with starch. This test makes iodine a widely used indicator for detecting starch.
Thyroid hormone: Thyroid hormones are iodine-containing hormones that regulate metabolism, growth, and development. The thyroid gland incorporates iodine into thyroxine and triiodothyronine.
Joseph Louis Gay-Lussac: Joseph Louis Gay-Lussac was a French chemist who investigated iodine and established its elemental character. His work helped confirm iodine as an element and popularized its name.
Astatine: Astatine is the radioactive halogen element with atomic number 85 and symbol At. Astatine lies below iodine in Group 17 but is far rarer and less chemically characterized.