An Etymological Dictionary of Astronomy and Astrophysics
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A member of a group of five chemical elements having closely related and similar properties. The halogens are: fluorine, chlorine, iodine, bromine, and astatine. They make up Group 17 of the → periodic table and can be found on the left-hand side of the → noble gases.

From Gk. halo- prefix from Gk. hals "salt" + → -gen.

A class of molecules that contain at least one → halogen atom bonded to → carbon. Organohalogens are abundant on the Earth where they are mainly produced through industrial and biological processes. They have been proposed as → biomarkers in the search for life on → exoplanets. Simple halogen hydrides have been detected in → interstellar medium sources and in → comets. → Methyl chloride (CH₃Cl), the most abundant organohalogen in the Earth's atmosphere, has both → natural and → synthetic production pathways (Fayolle et al., 2017, Nature Astronomy 1, 703).

From organo-, → organ, + → halogen.