Editing Halide

{{Short description|Chemical compound composed of a halogen atom and some other element}}
{{otheruses}}
{{See also|Organic halide}}
{{refimprove|date=March 2018}}
[[File:Atomic & ionic radii halides.svg|Radii in picometers of common halogen atoms (gray/black) and the corresponding halide anions (blue)|right|thumb|120px]]
In [[chemistry]], a '''halide''' (rarely '''halogenide'''<ref>{{Cite web|title=Definition of HALOGENIDE|url=https://www.merriam-webster.com/dictionary/halogenide|access-date=2022-01-07|website=www.merriam-webster.com|language=en}}</ref>) is a [[Binary phase|binary chemical compound]], of which one part is a [[halogen]] [[atom]] and the other part is an [[chemical element|element]] or [[radical (chemistry)|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 [[salt (chemistry)|salt]]s are halides; the ''hal-'' syllable in ''halide'' and ''[[halite]]'' reflects [[Halogen#Etymology|this correlation]].<ref>{{Greenwood&Earnshaw2nd| page = 82}}</ref>

A '''halide ion''' is a halogen atom bearing a negative charge. The common halide [[anion]]s are [[fluoride]] ({{chem2|F-}}), [[chloride]] ({{chem2|Cl-}}), [[bromide]] ({{chem2|Br-}}), and [[iodide]] ({{chem2|I-}}). Such ions are present in many [[ionic bonding|ionic]] halide salts. [[Halide mineral]]s contain halides. All these halide anions are colorless.  Halides also form covalent bonds, examples being colorless [[titanium tetrafluoride|TiF<sub>4</sub>]], colorless [[titanium tetrachloride|TiCl<sub>4</sub>]], orange [[titanium tetrabromide|TiBr<sub>4</sub>]], and brown [[titanium tetraiodide|TiI<sub>4</sub>]].  The heavier members TiCl<sub>4</sub>, TiBr<sub>4</sub>, TiI<sub>4</sub> can be distilled readily because they are molecular. The outlier is TiF<sub>4</sub>, [[melting point|m.p. 284 °C]], because it has a polymeric structure.  Fluorides often differ from the heavier halides.<ref>{{Greenwood&Earnshaw2nd| page = 694}}</ref>

==Reactions==
===Redox===
Halides cannot be reduced under the usual laboratory conditions, but they all can be oxidized to the parent halogens, which are [[diatomic]].  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 [[polyiodide]]s.

===Protonation===
Halides are conjugate bases of [[hydrogen halide]]s, which are all gases.  When the protonation is conducted in aqueous solution, [[hydrohalic acid]]s are produced.

===Reaction with silver ions===
Halide salts such as [[Potassium chloride|{{chem2|KCl}}]], [[Potassium bromide|{{chem2|KBr}}]] and [[Potassium iodide|{{chem2|KI}}]] are highly soluble in water to give colorless solutions. The solutions react readily with a solution of [[silver nitrate]] {{chem2|AgNO3}}. These three halides form solid [[precipitate]]s:<ref>{{Greenwood&Earnshaw2nd| page = 1184}}</ref>
* [[Silver chloride|{{chem2|AgCl}}]]: white
* [[Silver bromide|{{chem2|AgBr}}]]: pale yellow
* [[Silver iodide|{{chem2|AgI}}]]: yellow
Similar but slower reactions occur with [[alkyl halide]]s in place of alkali metal halides, as described in the [[Beilstein test]].

==Uses==
[[:Category:Metal halides|Metal halides]] are used in [[high-intensity discharge lamp]]s called [[metal halide lamp]]s, such as those used in  modern [[street light]]s.  These are more [[Energy conversion efficiency|energy-efficient]] than [[mercury-vapor lamp]]s, and have much better [[colour rendition]] than [[orange (colour)|orange]] [[Sodium-vapor lamp|high-pressure sodium lamps]]. Metal halide lamps are also commonly used in [[greenhouse]]s or in rainy climates to supplement natural [[sunlight]].

[[Silver halide]]s are used in [[photographic film]]s and [[photographic paper|papers]]. When the film is [[photographic processing|developed]], the silver halides which have been exposed to light are reduced to metallic silver, forming an image.

Halides are also used in [[Flux_(metallurgy)|solder paste]], commonly as a Cl or Br equivalent.<ref name="indium">{{Cite web |url=http://www.indium.com/halogen-free/assets/PDF/Indium8_9HF_Overview.pdf |title=Halogen-Free Solder Paste |access-date=2011-03-21 |archive-url=https://web.archive.org/web/20120317004413/http://www.indium.com/halogen-free/assets/PDF/Indium8_9HF_Overview.pdf |archive-date=2012-03-17 |url-status=dead }}</ref>

Synthetic [[organic chemistry]] often incorporates halogens into [[organohalide]] compounds.

==See also==
* [[Salinity]]
* [[Organohalide]]
* [[Hydrogen halide]]
* [[Silver halide]]

==References==
{{reflist}}

{{Authority control}}

[[Category:Salts]]
[[Category:Halides| ]]