halogen hăl´əjĕn , any kind of of the chemically active elements discovered in team 17 the the regular table; the name applies especially to fluorine (symbol F), chlorine (Cl), bromine (Br), and iodine (I). Astatine (At), previously known together alabamine, is a radioactive element additionally classed together a halogen; its many stable isotope (which go not occur in nature) has a half-life of much less than 8 1⁄2 hr. The chemical and also physical properties of astatine are not well known; that is believed to resemble iodine. The halogens are the best-defined family members of chemistry elements. Chemically they closely resemble one another; they space nonmetallic and type monovalent an unfavorable ions. They likewise exhibit an nearly perfect gradation of physics properties. Fluorine, a pale yellow gas, is the the very least dense and also chemically the many active, displacing the other halogens from their compounds and even displacing oxygen indigenous water. Chlorine, a yellow-green gas, is much more dense and also less reactive than fluorine. Bromine is a dark red liquid. Iodine is a grayish black color solid and also is the the very least chemically active of the four; however, amongst the nonmetals only oxygen is much more reactive than iodine. Pure halogens exist together diatomic molecules, e.g., Cl2; they form interhalogen compounds, i.e., compounds in between two halogens. The halogens type numerous link with various other elements. Through hydrogen they form hydrogen halides, who water options are dubbed hydrohalic acids, e.g., the water equipment of hydrogen chloride is dubbed hydrochloric acid. They type numerous steel halides, or salts, e.g., salt chloride, typical table salt. They also form halocarbons, compounds with carbon and also often other aspects such together hydrogen and also oxygen. Chloroform, iodoform, and carbon tetrachloride space halocarbons. Some various other halogen compounds space calomel (mercurous chloride), fluorite, sal ammoniac (ammonium chloride), corrosive sublimate (mercuric chloride), and also chlorine bleaches.

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