chemistry Chemistry is the scientific study of the properties and behavior of matter. It is a physical science within the natural sciences that studies the chemical elements that make up matter and chemical compound, compounds made of atoms, molecules a ...

, a halide (rarely halogenide) is a binary chemical compound, of which one part is a halogen

atom Atoms are the basic particles of the chemical elements. An atom consists of a atomic nucleus, nucleus of protons and generally neutrons, surrounded by an electromagnetically bound swarm of electrons. The chemical elements are distinguished fr ...

and the other part is an element or radical that is less electronegative (or more electropositive) than the halogen, to make a

fluoride Fluoride (). According to this source, is a possible pronunciation in British English. is an Inorganic chemistry, inorganic, Monatomic ion, monatomic Ion#Anions and cations, anion of fluorine, with the chemical formula (also written ), whose ...

chloride The term chloride refers to a compound or molecule that contains either a chlorine anion (), which is a negatively charged chlorine atom, or a non-charged chlorine atom covalently bonded to the rest of the molecule by a single bond (). The pr ...

, bromide, iodide, astatide, or theoretically tennesside compound. The

alkali metals The alkali metals consist of the chemical elements lithium (Li), sodium (Na), potassium (K),The symbols Na and K for sodium and potassium are derived from their Latin names, ''natrium'' and ''kalium''; these are still the origins of the names ...

combine directly with halogens under appropriate conditions forming halides of the general formula, MX (X = F, Cl, Br or I). Many

salt In common usage, salt is a mineral composed primarily of sodium chloride (NaCl). When used in food, especially in granulated form, it is more formally called table salt. In the form of a natural crystalline mineral, salt is also known as r ...

s 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

anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...

s are

(),

(), bromide (), and iodide (). Such ions are present in many ionic halide salts.

Halide mineral Halide minerals are those minerals with a dominant halide anion (, , and ). Complex halide minerals may also have Polyatomic ion, polyatomic anions. Examples include the following: *Atacamite *Avogadrite (K,Cs)BF *Bararite (β) *Bischofite * ...

s 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.

Reactions

Redox

Halides cannot be reduced under the usual laboratory conditions, but they all can be oxidized to the parent halogens, which are

diatomic Diatomic molecules () are molecules composed of only two atoms, of the same or different chemical elements. If a diatomic molecule consists of two atoms of the same element, such as hydrogen () or oxygen (), then it is said to be homonuclear mol ...

. Especially for iodide and less so for the lighter halides, intermediates can be observed and isolated. Best characterized is triiodide. Many related species are known, including a host of polyiodides.

Protonation

Halides are conjugate bases of hydrogen halides, which are all gases. When the protonation is conducted in aqueous solution, hydrohalic acids are produced.

Reaction with silver ions

Halide salts such as , and are highly soluble in water to give colorless solutions. The solutions react readily with a solution of silver nitrate . These three halides form solid precipitates: * : white * : pale yellow * : yellow Similar but slower reactions occur with alkyl halides in place of alkali metal halides, as described in the Beilstein test.

Uses

Metal halides Metal halides are compounds between metals and halogens. Some, such as sodium chloride are Ionic compound, ionic, while others are covalently bonded. A few metal halides are discrete molecules, such as uranium hexafluoride, but most adopt polymeric ...

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

greenhouse A greenhouse is a structure that is designed to regulate the temperature and humidity of the environment inside. There are different types of greenhouses, but they all have large areas covered with transparent materials that let sunlight pass an ...

s or in rainy climates to supplement natural

sunlight Sunlight is the portion of the electromagnetic radiation which is emitted by the Sun (i.e. solar radiation) and received by the Earth, in particular the visible spectrum, visible light perceptible to the human eye as well as invisible infrare ...

. Silver halides are used in

photographic film Photographic film is a strip or sheet of transparent film base coated on one side with a gelatin photographic emulsion, emulsion containing microscopically small light-sensitive silver halide crystals. The sizes and other characteristics of the ...

s and papers. When the film is developed, the silver halides which have been exposed to light are reduced to metallic silver, forming an image. Halides are also used in solder paste, commonly as a Cl or Br equivalent. Synthetic

organic chemistry Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic matter, organic materials, i.e., matter in its various forms that contain ...

often incorporates halogens into organohalide compounds.

References