Halide

Overview
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 than the halogen, to make a fluoride, chloride, bromide, iodide, or astatide compound. Many salts are halides. All Group 1 metals form halides with the halogens and they are white solids.

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.

Halides in organic chemistry
In organic chemistry halides represent a functional group. Any organic compound that contains a halogen atom can be considered a halide. Alkyl halides are organic compounds of the type R-X, containing an alkyl group R covalently bonded to a halogen X.

Pseudohalides resemble halides in their charge and reactivity; common examples are azides NNN-, isocyanate -NCO, Isocyanide, CN-, etc.

A chemical test for the detection of halogen in chemical substances is the Carius halogen method.

Halides in lighting
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.

HID (High-intensity discharge) lamps however, contribute highly to light pollution. Sodium-vapor are favored for this reason.

Halide compounds
Examples of halide compounds are:
 * sodium chloride (NaCl)
 * potassium chloride (KCl)
 * potassium iodide (KI)
 * lithium chloride (LiCl)
 * copper(II) chloride (CuCl2)
 * chlorine fluoride (ClF)
 * Bromomethane (CH3Br)
 * Iodoform (CHI3)
 * silver chloride (AgCl)