A halide is a binary compound, 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, or astatide compound. 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.
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.
Halides are also used in solder paste, commonly as a Cl or Br equivalent.
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)