halogeene

Halogeene, or halogens, are the elements of Group 17 in the periodic table: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). Tennessine (Ts) is a synthetic member that is extremely unstable and has no practical uses. Halogens are nonmetals with very high electronegativity and reactivity. In their elemental state they form diatomic molecules (F2, Cl2, Br2, I2); astatine and tennessine are not observed as stable diatomic species under normal conditions.

Reactivity and periodic trends are marked by high reactivity, especially for fluorine and chlorine. Reactivity generally decreases down the group. Halogens form compounds with almost every other element and commonly appear in the –1 oxidation state in many salts and in hydrogen halides (HX). Hydrogen fluoride (HF) is a comparatively weak acid in water, whereas HCl, HBr, and HI are strong acids. The elements also form interhalogen compounds (such as ClF, BrF) and a wide variety of halides with metals.

Natural occurrence and compounds: halogens occur mainly as halide minerals and salts in the environment. Fluorine is found in minerals like fluorite (CaF2); chloride, bromide, and iodide ions are abundant in seawater and various rocks. Halogens form essential and industrially important compounds, including hydrogen halides, interhalogen species, and a broad set of organic and inorganic halides.

Uses and significance: fluorine and fluoride compounds are used in toothpaste and electronics; chlorine is widely used for water disinfection and in the production of plastics such as PVC; bromine has applications in flame retardants and certain pharmaceuticals; iodine is essential for thyroid function and used in medical imaging and antiseptics. Astatine is mainly studied in research contexts; tennessine has no practical applications due to instability.

Naming: the term halogen derives from Greek halo-, salt, and gen-, forming or producing.