Halogen

A halogen is a group-17 element, such as fluorine, chlorine, bromine, or iodine. These elements commonly form singly charged halide ions and also form covalent compounds.

Their molecular elemental forms and their halide salts have different properties. Across the group, changing atomic size and electronic structure alters bond strengths, polarizability, and redox behavior rather than producing one universal reactivity ranking for every reaction.

Iodine is the chemical element with atomic number 53 and symbol $\mathrm{I}$. It is a halogen. Elemental iodine consists of ${\mathrm{I}}_2$ molecules and forms a dark molecular solid near room temperature. Iodide is the reduced anion ${\mathrm{I}}^{-}$; the different forms can interconvert in redox chemistry and have different spectroscopic behavior.^[ref]

Historical pharmaceutical preparation; its composition and clinical use must be identified by edition. ^[ref]

Historical pharmaceutical preparation; its composition and clinical use must be identified by edition. ^[ref]

Historical pharmaceutical preparation; its composition and clinical use must be identified by edition. ^[ref]

The mineral-rich residue historically obtained by burning collected seaweeds and leached as a source of iodine-bearing salts.

Iodate is the oxyanion $\mathrm{I}{\mathrm{O}}_3^{-}$, with iodine formally in oxidation state +5. It differs from iodide, in which iodine has oxidation state −1.

Reduction can convert iodate into lower-oxidation-state iodine species. Iodate occurs in some natural deposits and industrial feedstocks, connecting iodine extraction with oxidation-reduction chemistry.

The potassium salt of iodate, formed together with potassium iodide in the reaction of iodine with hot potassium hydroxide.

Triiodide is the anion ${\mathrm{I}}_3^{-}$, formed in the equilibrium ${\mathrm{I}}_2+{\mathrm{I}}^{-}\rightleftharpoons {\mathrm{I}}_3^{-}$. Formation of triiodide can increase the amount of iodine accommodated in an aqueous iodide-containing solution.

The total dissolved iodine inventory therefore need not equal the concentration of free molecular iodine. Interpreting an optical or titration measurement requires the relevant species balance.