halogjene

Halogens are a group of elements in the periodic table, consisting of fluorine, chlorine, bromine, iodine, astatine, and tennessine. They occupy group 17 (VIIA) and are nonmetals with seven valence electrons. They are highly reactive and readily form compounds with many elements, especially alkali and alkaline earth metals, to produce salts. In elemental form, they are diatomic molecules.

They have high electronegativity and electron affinity; reactivity generally decreases down the group. Fluorine is the most reactive, while astatine is least studied due to its radioactivity. They form hydrogen halides (HF, HCl, HBr, HI) when bonded to hydrogen, which are weak to strong acids depending on the halogen. In compounds they predominantly exhibit the -1 oxidation state as halides.

Halogens occur in minerals and seawater. Industrially, chlorine is used to produce PVC and disinfect water; fluorine forms many fluorinated polymers such as PTFE; bromine is used in flame retardants; iodine is essential in nutrition and used in antiseptics. Astatine is extremely rare; tennessine is synthetic and short‑lived.

Biologically, chloride and iodide are essential nutrients; fluoride is used to prevent dental decay in small amounts, but excessive exposure can be harmful. Halogens are highly reactive and corrosive, requiring proper handling and storage.

The term halogen comes from Greek halos, salt, and genes, meaning “salt former.” The group was identified in the 19th century through the work of several chemists.