halogenen

Halogens are a group of six chemical elements in Group 17 of the periodic table: fluorine, chlorine, bromine, iodine, astatine, and the synthetic element tennessine. They are highly reactive nonmetals, characterized by high electronegativity and a tendency to gain one electron to achieve a stable octet. In aqueous solutions they form halide ions (F-, Cl-, Br-, I-, At-). Elemental halogens, except astatine and tennessine, exist as diatomic molecules F2, Cl2, Br2, and I2; fluorine and chlorine are gases at room temperature, bromine is a liquid, and iodine is a solid. Astatine is rare and radioactive, and tennessine is synthetically produced and short-lived.

Chemically, halogens commonly form compounds with hydrogen to give hydrohalic acids (HF, HCl, HBr, HI). Acidity increases down the group, with HI and HBr being strong acids in water, while HF is comparatively weak. They also form a wide range of interhalogen compounds (e.g., ClF, BrCl) and many metal halides. Their chemistry spans oxidation states from -1 to +7.

Halogens occur naturally in minerals and in seawater and sediments. They have numerous applications: chlorine for disinfection and synthetic chemistry; fluorides in dental products; iodine as an essential nutrient; bromine in flame retardants and photography; astatine mainly in research contexts; tennessine only in laboratories and studies of superheavy elements.

Environmental and safety notes: halogens can impact the atmosphere (chlorine and bromine catalysts in ozone depletion) and certain halide species can be toxic at high concentrations. Etymology: the name halogen derives from Greek halos, salt-producing.