In chemistry, a halide (rarely halogenide) is a binary chemical 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, 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.
A halide ion is a halogen atom bearing a negative charge. The common halide anions are fluoride (F), chloride (Cl), bromide (Br), and iodide (I). Such ions are present in many ionic halide salts. Halide minerals contain halides. All these halide anions are colorless. Halides also form covalent bonds, examples being colorless TiF4, colorless TiCl4, orange TiBr4, and brown TiI4. 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.