Editing Uranium (section)

===Halides===
[[File:Uranium hexafluoride crystals sealed in an ampoule.jpg|thumb|[[Uranium hexafluoride]] is the feedstock used to separate uranium-235 from natural uranium.|alt=Snow-like substance in a sealed glass ampoule.]]
<!--[[File:Uranium-hexafluoride-2D-V2.svg|thumb|upright|[[Uranium hexafluoride]] is the feedstock used to separate uranium-235 from natural uranium.|alt=Skeletal diagram of a chemical compound having a uranium atom in its center bonded to 6 fluorine atoms.]]-->
All uranium fluorides are created using [[uranium tetrafluoride]] ({{chem|UF|4}}); {{chem|UF|4}} itself is prepared by hydrofluorination of uranium dioxide.{{sfn|Seaborg|1968|p=782}} Reduction of {{chem|UF|4}} with hydrogen at 1000&nbsp;°C produces [[uranium trifluoride]] ({{chem|UF|3}}). Under the right conditions of temperature and pressure, the reaction of solid {{chem|UF|4}} with gaseous [[uranium hexafluoride]] ({{chem|UF|6}}) can form the intermediate fluorides of {{chem|U|2|F|9}}, {{chem|U|4|F|17}}, and [[Uranium pentafluoride|{{chem|UF|5}}]].{{sfn|Seaborg|1968|p=782}}

At room temperatures, {{chem|UF|6}} has a high [[vapor pressure]], making it useful in the [[gaseous diffusion]] process to separate the rare uranium-235 from the common uranium-238 isotope. This compound can be prepared from uranium dioxide and uranium hydride by the following process:{{sfn|Seaborg|1968|p=782}}

:{{chem|UO|2}} + 4 HF → {{chem|UF|4}} + 2 {{chem|H|2|O}} (500&nbsp;°C, endothermic)
:{{chem|UF|4}} + {{chem|F|2}} → {{chem|UF|6}} (350&nbsp;°C, endothermic)

The resulting {{chem|UF|6}}, a white solid, is highly [[chemical reaction|reactive]] (by fluorination), easily [[sublimation (chemistry)|sublimes]] (emitting a vapor that behaves as a nearly [[ideal gas]]), and is the most volatile compound of uranium known to exist.{{sfn|Seaborg|1968|p=782}}

One method of preparing [[uranium tetrachloride]] ({{chem|UCl|4}}) is to directly combine [[chlorine]] with either uranium metal or uranium hydride. The reduction of {{chem|UCl|4}} by hydrogen produces [[uranium trichloride]] ({{chem|UCl|3}}) while the higher chlorides of uranium are prepared by reaction with additional chlorine.{{sfn|Seaborg|1968|p=782}} All uranium chlorides react with water and air.

[[Bromide]]s and [[iodide]]s of uranium are formed by direct reaction of, respectively, [[bromine]] and [[iodine]] with uranium or by adding {{chem|UH|3}} to those element's acids.{{sfn|Seaborg|1968|p=782}} Known examples include: [[Uranium(III) bromide|{{chem|UBr|3}}]], [[Uranium(IV) bromide|{{chem|UBr|4}}]], [[Uranium(III) iodide|{{chem|UI|3}}]], and [[Uranium(IV) iodide|{{chem|UI|4}}]]. {{chem|UI|5}} has never been prepared. Uranium oxyhalides are water-soluble and include [[Uranyl fluoride|{{chem|UO|2|F|2}}]], {{chem|UOCl|2}}, [[Uranyl chloride|{{chem|UO|2|Cl|2}}]], and [[Uranyl bromide|{{chem|UO|2|Br|2}}]]. Stability of the oxyhalides decrease as the [[atomic weight]] of the component halide increases.{{sfn|Seaborg|1968|p=782}}