Editing Uranium (section)

==Characteristics==
[[File:Nuclear fission.svg|thumb|left|upright|A neutron-induced nuclear fission event involving uranium-235|alt=A diagram showing a chain transformation of uranium-235 to uranium-236 to barium-141 and krypton-92]]
Uranium is a silvery white, weakly radioactive [[metal]]. It has a [[Hardnesses of the elements (data page)|Mohs hardness]] of 6, sufficient to scratch glass and roughly equal to that of [[titanium]], [[rhodium]], [[manganese]] and [[niobium]]. It is [[malleability|malleable]], [[ductility|ductile]], slightly [[paramagnetism|paramagnetic]], strongly [[electronegativity|electropositive]] and a poor [[electrical conductivity|electrical conductor]].<ref name="SciTechEncy" /><ref name="LANL">{{cite book |author=Hammond, C. R. |title=The Elements, in Handbook of Chemistry and Physics |edition=81st |publisher=CRC press |date=2000 |isbn=978-0-8493-0481-1 |url=http://www-d0.fnal.gov/hardware/cal/lvps_info/engineering/elements.pdf}}</ref> Uranium metal has a very high [[density]] of 19.1&nbsp;g/cm{{sup|3}},<ref>{{cite web |title=Uranium |url=http://www.rsc.org/periodic-table/element/92/uranium |publisher=Royal Society of Chemistry}}</ref> denser than [[lead]] (11.3&nbsp;g/cm{{sup|3}}),<ref>{{cite web |title=Lead |url=http://www.rsc.org/periodic-table/element/82/lead |publisher=Royal Society of Chemistry}}</ref> but slightly less dense than [[tungsten]] and [[gold]] (19.3&nbsp;g/cm{{sup|3}}).<ref>{{cite web |title=Tungsten |url=http://www.rsc.org/periodic-table/element/74/tungsten |publisher=Royal Society of Chemistry}}</ref><ref>{{cite web |title=Gold |url=http://www.rsc.org/periodic-table/element/79/gold |publisher=Royal Society of Chemistry}}</ref>

Uranium metal reacts with almost all non-metallic elements (except [[noble gas]]es) and their [[chemical compound|compounds]], with reactivity increasing with temperature.<ref name="ColumbiaEncy">{{cite encyclopedia |title=uranium |encyclopedia=Columbia Electronic Encyclopedia|url=http://www.answers.com/uranium |publisher=Columbia University Press |edition=6th |access-date=27 September 2008|archive-date=27 July 2011|archive-url=https://web.archive.org/web/20110727194715/http://www.answers.com/uranium|url-status=dead}}</ref> [[Hydrochloric acid|Hydrochloric]] and [[nitric acid]]s dissolve uranium, but non-oxidizing acids other than hydrochloric acid attack the element very slowly.<ref name="SciTechEncy" /> When finely divided, it can react with cold water; in air, uranium metal becomes coated with a dark layer of [[uranium dioxide]].<ref name="LANL" /> Uranium in ores is extracted chemically and converted into [[uranium dioxide]] or other chemical forms usable in industry.

Uranium-235 was the first isotope that was found to be [[fissile]]. Other naturally occurring isotopes are fissionable, but not fissile.{{cn|date=December 2024}} On bombardment with slow neutrons, uranium-235 most of the time splits into two smaller [[atomic nucleus|nuclei]], releasing nuclear [[binding energy]] and more neutrons. If too many of these neutrons are absorbed by other uranium-235 nuclei, a [[nuclear chain reaction]] occurs that results in a burst of heat or (in some circumstances) an explosion. In a nuclear reactor, such a chain reaction is slowed and controlled by a [[neutron poison]], absorbing some of the free neutrons. Such neutron absorbent materials are often part of reactor [[control rod]]s (see [[nuclear reactor physics]] for a description of this process of reactor control).

As little as {{cvt|15|lb}} of uranium-235 can be used to make an atomic bomb.<ref name="EncyIntel">{{cite encyclopedia |encyclopedia=Encyclopedia of Espionage, Intelligence, and Security|publisher=The Gale Group, Inc. |title=uranium |url=http://www.answers.com/uranium|access-date=27 September 2008|archive-date=27 July 2011|archive-url=https://web.archive.org/web/20110727194715/http://www.answers.com/uranium|url-status=dead}}</ref> The nuclear weapon detonated over [[Hiroshima]], called [[Little Boy]], relied on uranium fission. However, the first nuclear bomb (the ''Gadget'' used at [[Trinity (nuclear test)|Trinity]]) and the bomb that was detonated over Nagasaki ([[Fat Man]]) were both plutonium bombs.

Uranium metal has three [[allotropy|allotropic]] forms:<ref>{{cite book |url=https://books.google.com/books?id=KWGu-LYMYjMC&pg=PA108 |page=108 |title=Applications of Texture Analysis |author=Rollett, A. D. |publisher=John Wiley and Sons |date=2008 |isbn=978-0-470-40835-3}}</ref>
* α ([[orthorhombic]]) stable up to {{convert|668|C}}. Orthorhombic, [[space group]] No. 63, ''Cmcm'', [[lattice parameter]]s ''a''&nbsp;= 285.4&nbsp;pm, ''b''&nbsp;= 587&nbsp;pm, ''c''&nbsp;= 495.5&nbsp;pm.<ref name="Grenthe">{{cite book|last1=Grenthe |first1=Ingmar |first2=Janusz |last2=Drożdżyński |first3=Takeo |last3=Fujino |first4=Edgar C. |last4=Buck |author-link5=Thomas Albrecht-Schönzart |first5=Thomas E. |last5=Albrecht-Schmitt |first6=Stephen F. |last6=Wolf |contribution=Uranium |title=The Chemistry of the Actinide and Transactinide Elements |editor1-first=Lester R. |editor1-last=Morss |editor2-first=Norman M. |editor2-last=Edelstein |editor3-first=Jean |editor3-last=Fuger |edition=3rd |date=2006 |volume=5 |publisher=Springer |location=Dordrecht, the Netherlands |pages=52–160 |url=http://radchem.nevada.edu/classes/rdch710/files/thorium.pdf |doi=10.1007/1-4020-3598-5_5 |url-status=dead |archive-url=https://web.archive.org/web/20160307160941/http://radchem.nevada.edu/classes/rdch710/files/Thorium.pdf |archive-date=7 March 2016 |isbn=978-1-4020-3555-5 }}</ref>
* β ([[tetragonal]]) stable from {{convert|668|to|775|C}}. Tetragonal, space group ''P''4<sub>2</sub>/''mnm'', ''P''4<sub>2</sub>''nm'', or ''P''4''n''2, lattice parameters ''a''&nbsp;= 565.6&nbsp;pm, ''b''&nbsp;= ''c''&nbsp;= 1075.9&nbsp;pm.<ref name="Grenthe" />
* γ ([[body-centered cubic]]) from {{convert|775|C}} to melting point—this is the most malleable and ductile state. Body-centered cubic, lattice parameter ''a''&nbsp;=&nbsp;352.4&nbsp;pm.<ref name="Grenthe" />