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.

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.^[1]

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

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.

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)

• Salinity
• Functional groups

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