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A halide is a binary phase, of which one part is a halogen atom and the other part is an element or radical that is less electronegative (or more electropositive) than the halogen, to make a fluoride, chloride, bromide, iodide, astatide, or theoretically tennesside compound. The alkali metals combine directly with halogens under appropriate conditions forming halides of the general formula, MX (X = F, Cl, Br or I). Many salts are halides; the hal- syllable in halide and halite reflects this correlation. All Group 1 metals form halides that are white solids at room temperature.
A halide ion is a halogen atom bearing a negative charge. The halide anions are fluoride (F−), chloride (Cl−), bromide (Br−), iodide (I−) and astatide (At−). Such ions are present in all ionic halide salts. Halide minerals contain halides.
All these halides are colourless, high melting crystalline solids having high negative enthalpies of formation.
For organic compounds containing halides, the Beilstein test is used.
Metal halides are used in high-intensity discharge lamps called metal halide lamps, such as those used in modern street lights. These are more energy-efficient than mercury-vapor lamps, and have much better colour rendition than orange high-pressure sodium lamps. Metal halide lamps are also commonly used in greenhouses or in rainy climates to supplement natural sunlight.
Examples of halide compounds are:
- Sodium chloride (NaCl)
- Potassium chloride (KCl)
- Potassium iodide (KI)
- Lithium chloride (LiCl)
- Copper(II) chloride (CuCl2)
- Silver chloride (AgCl)
- Calcium chloride (CaCl2)
- Chlorine fluoride (ClF)
- Hydrogen chloride (HCl)