Editing Americium (section)

==Chemical properties==
Americium metal readily reacts with oxygen and dissolves in aqueous [[acid]]s. The most stable [[oxidation state]] for americium is +3.<ref name="p4">Penneman, p. 4</ref> The chemistry of americium(III) has many similarities to the chemistry of [[lanthanide]](III) compounds. For example, trivalent americium forms insoluble [[fluoride]], [[oxalate]], [[iodate]], [[hydroxide]], [[phosphate]] and other salts.<ref name="p4" /> Compounds of americium in oxidation states +2, +4, +5, +6 and +7 have also been studied. This is the widest range that has been observed with actinide elements. The color of americium compounds in aqueous solution is as follows: Am<sup>3+</sup> (yellow-reddish), Am<sup>4+</sup> (yellow-reddish), {{chem2|Am^{V}O2+}}; (yellow), {{chem2|Am^{VI}O2(2+)}} (brown) and {{chem2|Am^{VII}O6(5-)}} (dark green).<ref>[http://www.chemie-master.de/FrameHandler.php?loc=http://www.chemie-master.de/pse/pse.php?modul=Am Americium] {{Webarchive|url=https://web.archive.org/web/20190609181845/http://www.chemie-master.de/FrameHandler.php?loc=http%3A%2F%2Fwww.chemie-master.de%2Fpse%2Fpse.php%3Fmodul%3DAm |date=9 June 2019 }}, Das Periodensystem der Elemente für den Schulgebrauch (The periodic table of elements for schools) chemie-master.de (in German), Retrieved 28 November 2010</ref><ref name="g1265">Greenwood, p. 1265</ref> The absorption spectra have sharp peaks, due to ''f''-''f'' transitions' in the visible and near-infrared regions. Typically, Am(III) has absorption maxima at ca. 504 and 811&nbsp;nm, Am(V) at ca. 514 and 715&nbsp;nm, and Am(VI) at ca. 666 and 992&nbsp;nm.<ref>Penneman, pp. 10–14</ref><ref name="amoh4" /><ref name="carbonate" /><ref name="haxav" />

Americium compounds with oxidation state +4 and higher are strong oxidizing agents, comparable in strength to the [[permanganate]] ion ({{chem2|MnO4-}}) in acidic solutions.<ref name = "HOWI_1956">Wiberg, p. 1956</ref> Whereas the Am<sup>4+</sup> ions are unstable in solutions and readily convert to Am<sup>3+</sup>, compounds such as [[americium dioxide]] (AmO<sub>2</sub>) and [[americium(IV) fluoride]] (AmF<sub>4</sub>) are stable in the solid state.

The pentavalent oxidation state of americium was first observed in 1951.<ref>{{cite journal|title=The Pentavalent State of Americium|last1=Werner|first1=L. B.|last2=Perlman|first2=I.|journal=Journal of the American Chemical Society|volume=73|page=495|date=1951|issue=1 |doi=10.1021/ja01145a540|bibcode=1951JAChS..73..495W |hdl=2027/mdp.39015086479774|hdl-access=free}}</ref> In acidic aqueous solution the {{chem2|AmO2+}} ion is unstable with respect to [[disproportionation]].<ref>{{cite journal|last1=Hall|first1=G.|title=The self-reduction of americium(V) and (VI) and the disproportionation of americium(V) in aqueous solution|journal=Journal of Inorganic and Nuclear Chemistry|volume=4|page=296|date=1957|doi=10.1016/0022-1902(57)80011-6|issue=5–6|last2=Markin|first2=T. L.}}</ref><ref>{{cite journal|last1=Coleman|first1=James S.|title=The Kinetics of the Disproportionation of Americium(V)|journal=Inorganic Chemistry|volume=2|page=53|date=1963|doi=10.1021/ic50005a016}}</ref><ref name="g1275">Greenwood, p. 1275</ref> The reaction

: {{chem2|3[AmO2]+ + 4H+ -> 2[AmO2](2+) + Am(3+) + 2H2O}}

is typical. The chemistry of Am(V) and Am(VI) is comparable to the chemistry of [[uranium]] in those oxidation states. In particular, compounds like {{chem2|Li3AmO4}} and {{chem2|Li6AmO6}} are comparable to [[uranate]]s and the ion {{chem2|AmO2(2+)}} is comparable to the [[uranyl]] ion, {{chem2|UO2(2+)}}. Such compounds can be prepared by oxidation of Am(III) in dilute nitric acid with [[ammonium persulfate]].<ref>{{cite journal|last1=Asprey|first1=L. B.|title=A New Valence State of Americium, Am(Vi)1|last2=Stephanou|first2=S. E.|last3=Penneman|first3=R. A.|journal=Journal of the American Chemical Society |volume=72|page=1425| date=1950|doi=10.1021/ja01159a528|issue=3|bibcode=1950JAChS..72.1425A | url=https://digital.library.unt.edu/ark:/67531/metadc1020623/}}</ref> Other oxidising agents that have been used include [[silver(I) oxide]],<ref name="haxav">{{cite journal|last1=Asprey|first1=L. B.|last2=Stephanou|first2=S. E.|last3=Penneman|first3=R. A.|title=Hexavalent Americium|journal=Journal of the American Chemical Society|volume=73|page=5715|date=1951|doi=10.1021/ja01156a065|issue=12|bibcode=1951JAChS..73.5715A }}</ref> [[ozone]] and [[sodium persulfate]].<ref name="carbonate">{{cite journal|last1=Coleman|first1=J. S.|last2=Keenan|first2=T. K.|last3=Jones|first3=L. H.|last4=Carnall|first4=W. T.|last5=Penneman|first5=R. A.|title=Preparation and Properties of Americium(VI) in Aqueous Carbonate Solutions|journal=Inorganic Chemistry|volume=2|page=58|date=1963|doi=10.1021/ic50005a017}}</ref>