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Inchemistry, ahalide (rarelyhalogenide[1]) is abinary chemical compound, of which one part is ahalogenatom and the other part is anelement orradical that is lesselectronegative (or more electropositive) than the halogen, to make afluoride,chloride,bromide,iodide,astatide, or theoreticallytennesside compound. Thealkali metals combine directly with halogens under appropriate conditions forming halides of the general formula, MX (X = F, Cl, Br or I). Manysalts are halides; thehal- syllable inhalide andhalite reflectsthis correlation.[2]
Ahalide ion is a halogen atom bearing a negative charge. The common halideanions arefluoride (F−),chloride (Cl−),bromide (Br−), andiodide (I−). Such ions are present in manyionic halide salts.Halide minerals contain halides. All these halide anions are colorless. Halides also form covalent bonds, examples being colorlessTiF4, colorlessTiCl4, orangeTiBr4, and brownTiI4. The heavier members TiCl4, TiBr4, TiI4 can be distilled readily because they are molecular. The outlier is TiF4,m.p. 284 °C, because it has a polymeric structure. Fluorides often differ from the heavier halides.[3]
Halides cannot be reduced under the usual laboratory conditions, but they all can be oxidized to the parent halogens, which arediatomic. Especially for iodide and less so for the lighter halides, intermediates can be observed and isolated. Best characterized istriiodide. Many related species are known, including a host ofpolyiodides.
Halides are conjugate bases ofhydrogen halides, which are all gases. When the protonation is conducted in aqueous solution,hydrohalic acids are produced.
Halide salts such asKCl,KBr andKI are highly soluble in water to give colorless solutions. The solutions react readily with a solution ofsilver nitrateAgNO3. These three halides form solidprecipitates:[4]
Similar but slower reactions occur withalkyl halides in place of alkali metal halides, as described in theBeilstein test.
Metal halides are used inhigh-intensity discharge lamps calledmetal halide lamps, such as those used in modernstreet lights. These are moreenergy-efficient thanmercury-vapor lamps, and have much bettercolour rendition thanorangehigh-pressure sodium lamps. Metal halide lamps are also commonly used ingreenhouses or in rainy climates to supplement naturalsunlight.
Silver halides are used inphotographic films andpapers. When the film isdeveloped, the silver halides which have been exposed to light are reduced to metallic silver, forming an image.
Halides are also used insolder paste, commonly as a Cl or Br equivalent.[5]
Syntheticorganic chemistry often incorporates halogens intoorganohalide compounds.
