Editing Actinium (section)

==Properties==
Actinium is a soft, silvery-white,<ref name="blueglow" /><ref name="brit">''Actinium'', in Encyclopædia Britannica, 15th edition, 1995, p. 70</ref> [[radioactive]], metallic element. Its estimated [[shear modulus]] is similar to that of [[lead]].<ref>Seitz, Frederick and Turnbull, David (1964) [https://books.google.com/books?id=F9V3a-0V3r8C&pg=PA289 ''Solid state physics: advances in research and applications'']. Academic Press. {{ISBN|0-12-607716-9}} pp. 289–291</ref> Owing to its strong radioactivity, actinium glows in the dark with a pale blue light, which originates from the surrounding air ionized by the emitted energetic particles.<ref>{{cite book |author=Richard A. Muller |title=Physics and Technology for Future Presidents: An Introduction to the Essential Physics Every World Leader Needs to Know |url=https://books.google.com/books?id=jMWCDsJesbcC&pg=PA136 |date= 2010 |publisher=Princeton University Press |isbn=978-0-691-13504-5 |pages=136–}}</ref> Actinium has similar chemical properties to [[lanthanum]] and other lanthanides, and therefore these elements are difficult to separate when extracting from uranium ores. [[Solvent extraction]] and [[ion chromatography]] are commonly used for the separation.<ref>{{cite journal |title = Chemistry of the Actinide Elements |volume = 1 |pages = 245–262 |date = 1952 |first1 = J. J. |last1 = Katz |doi = 10.1146/annurev.ns.01.120152.001333 |journal = [[Annual Review of Nuclear Science]] |last2 = Manning |first2 = W. M. |bibcode = 1952ARNPS...1..245K }}</ref>

The first element of the [[actinide]]s, actinium gave the set its name, much as [[lanthanum]] had done for the [[lanthanide]]s. The actinides are much more diverse than the lanthanides<ref name="Jorgensen">{{cite journal |last1=Jørgensen |first1=Christian |date=1973 |title=The Loose Connection between Electron Configuration and the Chemical Behavior of the Heavy Elements (Transuranics) |journal=Angewandte Chemie International Edition |volume=12 |issue=1 |pages=12–19 |doi=10.1002/anie.197300121}}</ref> and therefore it was not until 1945 that the most significant change to [[Dmitri Mendeleev]]'s [[periodic table]] since the recognition of the lanthanides, the [[actinide concept|introduction of the actinides]], was generally accepted after [[Glenn T. Seaborg]]'s research on the [[transuranium element]]s<ref>{{cite journal |title = The Transuranium Elements |first = Glenn T. |last = Seaborg |journal = Science |volume = 104 |issue = 2704 |date = 1946 |pages = 379–386 |jstor=1675046 |doi = 10.1126/science.104.2704.379 |pmid = 17842184 |bibcode = 1946Sci...104..379S }}</ref> (although it had been proposed as early as 1892 by British chemist Henry Bassett).<ref name="Thyssen">{{Cite book |last1=Thyssen |first1=P. |title=Handbook on the Physics and Chemistry of Rare Earths |last2=Binnemans |first2=K. |date=2011 |publisher=Elsevier |isbn=978-0-444-53590-0 |editor-last=Gschneidner |editor-first=K. A. Jr. |volume=41 |location=Amsterdam |pages=1–94 |chapter=Accommodation of the Rare Earths in the Periodic Table: A Historical Analysis |doi=10.1016/B978-0-444-53590-0.00001-7 |editor-last2=Bünzli |editor-first2=J-C.G |editor-last3=Vecharsky |editor-first3=Bünzli}}</ref>

Actinium reacts rapidly with oxygen and moisture in air forming a white coating of [[actinium oxide]] that impedes further oxidation.<ref name="blueglow">{{cite journal |title = Preparation of Actinium Metal |first1 = Joseph G. |last1 = Stites |journal = J. Am. Chem. Soc. |date = 1955 |volume = 77 |issue = 1 |pages = 237–240 |doi = 10.1021/ja01606a085 |last2 = Salutsky |first2 = Murrell L. |last3 = Stone |first3 = Bob D.|bibcode = 1955JAChS..77..237S }}</ref> As with most lanthanides and actinides, actinium exists in the [[oxidation state]] +3, and the Ac<sup>3+</sup> ions are colorless in solutions.<ref name="bse" /> The oxidation state +3 originates from the [Rn] 6d<sup>1</sup>7s<sup>2</sup> electronic configuration of actinium, with three valence electrons that are easily donated to give the stable closed-shell structure of the [[noble gas]] [[radon]].<ref name="brit" /> Although the 5f orbitals are unoccupied in an actinium atom, it can be used as a valence orbital in actinium complexes and hence it is generally considered the first 5f element by authors working on it.<ref>{{cite journal |last1=Tomeček |first1=Josef |last2=Li |first2=Cen |first3=Georg |last3=Schreckenbach |date=2023 |title=Actinium coordination chemistry: A density functional theory study with monodentate and bidentate ligands |url= |journal=Journal of Computational Chemistry |volume=44 |issue=3 |pages=334–345 |doi=10.1002/jcc.26929 |pmid=35668552 |s2cid=249433367 |access-date=}}</ref><ref>{{cite journal |last1=Deblonde |first1=Gauthier J.-P. |last2=Zavarin |first2=Mavrik |first3=Annie B. |last3=Kersting |date=2021 |title=The coordination properties and ionic radius of actinium: A 120-year-old enigma |url= |journal=Coordination Chemistry Reviews |volume=446 |issue= |page=214130 |doi=10.1016/j.ccr.2021.214130 |access-date=|doi-access=free }}</ref><ref name="AcNatureChem"/> Ac<sup>3+</sup> is the largest of all known tripositive ions and its first coordination sphere contains approximately 10.9 ± 0.5 water molecules.<ref>{{cite journal |last1=Ferrier |first1=Maryline G. |last2=Stein |first2=Benjamin W. |first3=Enrique R. |last3=Batista |first4=John M. |last4=Berg |first5=Eva R. |last5=Birnbaum |first6=Jonathan W. |last6=Engle |first7=Kevin D. |last7=John |first8=Stosh A. |last8=Kozimor |first9=Juan S. |last9=Lezama Pacheco |first10=Lindsay N. |last10=Redman |date=2017 |title=Synthesis and Characterization of the Actinium Aquo Ion |journal=ACS Central Science |volume=3 |issue=3 |pages=176–185 |doi=10.1021/acscentsci.6b00356|pmid=28386595 |pmc=5364452 }}</ref>