Editing Rubidium (section)

==Characteristics==
=== Physical properties ===
[[File:RbH.JPG|thumb|left|Partially molten rubidium metal in an ampoule]]
Rubidium is a very soft, [[ductility|ductile]], silvery-white metal.<ref name=Ohly>{{cite book |last=Ohly |first=Julius |date=1910 |chapter=Rubidium |title=Analysis, detection and commercial value of the rare metals |publisher=Mining Science Pub. Co. |chapter-url=https://books.google.com/books?id=dGUuAQAAIAAJ |via=Google books }}</ref> It has a melting point of {{convert|39.3|°C|°F}} and a boiling point of {{convert|688|°C|°F}}.<ref name="www.rsc.org">{{cite web |title=Rubidium |department=Element information, properties and uses |series=Periodic Table |url=https://www.rsc.org/periodic-table/element/37/rubidium |access-date=2024-09-09 |website=www.rsc.org}}</ref> It forms [[amalgam (chemistry)|amalgams]] with [[mercury (element)|mercury]] and [[alloy]]s with [[gold]], [[iron]], [[caesium]], [[sodium]], and [[potassium]], but not [[lithium]] (despite rubidium and lithium being in the same periodic group).<ref name=HollemanAF>{{cite book |first1 = Arnold F. |last1 = Holleman |last2 = Wiberg |first2 = Egon |last3 =Wiberg |first3 = Nils |date = 1985 |chapter = Vergleichende Übersicht über die Gruppe der Alkalimetalle |trans-chapter=Brief overview of the Alkalai metal group |title = Lehrbuch der Anorganischen Chemie |lang = de |trans-title=Textbook of Inorganic Chemistry |edition = 91–100 |publisher = Walter de Gruyter |isbn = 978-3-11-007511-3 |pages = 953–955 }}</ref> Rubidium and potassium show a very similar purple color in the [[flame test]], and distinguishing the two elements requires more sophisticated analysis, such as spectroscopy.<ref>{{cite journal |last1=Ahrens |first1=L.H. |last2=Pinson |first2=W.H. |last3=Kearns |first3=Makgaret M. |date=1952-01-01 |title=Association of rubidium and potassium and their abundance in common igneous rocks and meteorites |journal=[[Geochimica et Cosmochimica Acta]] |volume=2 |issue=4 |pages=229–242 |issn=0016-7037 |url=https://dx.doi.org/10.1016/0016-7037%2852%2990017-3|bibcode=1952GeCoA...2..229A |doi=10.1016/0016-7037(52)90017-3 }}</ref>

=== Chemical properties ===
[[File:Rb&Cs crystals.jpg|left|thumb|Rubidium crystals (silvery) compared to [[caesium]] crystals (golden)]]
Rubidium is the second most [[Electronegativity|electropositive]] of the stable alkali metals and has a very low first [[ionization energy]] of only 403&nbsp;kJ/mol.<ref name="www.rsc.org" /> It has an electron configuration of [Kr]5s<sup>1</sup> and is photosensitive.<ref name="Hart-1973" />{{rp|382}} Due to its strong electropositive nature, rubidium reacts explosively with water<ref>{{Cite book |last1=Cotton |first1=F. Albert |title=Advanced inorganic chemistry: a comprehensive text |last2=Wilkinson |first2=Geoffrey |date=1972 |publisher=Interscience Publishers |isbn=978-0-471-17560-5 |edition=3d ed., completely rev |location=New York |page=190}}</ref> to produce rubidium hydroxide and hydrogen gas.<ref name="Hart-1973" />{{rp|383}} As with all the alkali metals, the reaction is usually vigorous enough to ignite metal or the [[hydrogen]] gas produced by the reaction, potentially causing an explosion.<ref>{{Cite web |last=Stanford University |title=Information on Alkali Metals – Stanford Environmental Health & Safety |url=https://ehs.stanford.edu/reference/information-alkali-metals |access-date=2024-09-12 |language=en-US}}</ref> Rubidium, being denser than potassium, sinks in water, reacting violently; caesium explodes on contact with water.<ref>{{Cite web |title=Reactions of the Group 1 elements with water |author=Jim Clark|url=https://www.chemguide.co.uk/inorganic/group1/reacth2o.html |access-date=2024-09-12 |website=www.chemguide.co.uk}}</ref> However, the reaction rates of all alkali metals depend upon surface area of metal in contact with water, with small metal droplets giving explosive rates.<ref>Maustellar, J. W, F Tepper, and S. J. (Sheridan Joseph) Rodgers. "Alkali Metal Handling and Systems Operating Techniques" Prepared under the Direction of the American Nuclear Society for the United States Atomic Energy Commission. New York: Gordon and Breach, 1968.</ref> Rubidium has also been reported to ignite spontaneously in air.<ref name="Ohly" />

===Compounds===
{{category see also|Rubidium compounds}}
[[File:Rb9O2 cluster.png|thumb|left|upright=0.5|{{chem|Rb|9|O|2}} cluster|alt= The ball-and-stick diagram shows two regular octahedra which are connected to each other by one face. All nine vertices of the structure are purple spheres representing rubidium, and at the centre of each octahedron is a small red sphere representing oxygen.]]
[[Rubidium chloride]] (RbCl) is probably the most used rubidium compound: among several other chlorides, it is used to induce living cells to take up [[DNA]]; it is also used as a biomarker, because in nature, it is found only in small quantities in living organisms and when present, replaces potassium. Other common rubidium compounds are the corrosive [[rubidium hydroxide]] (RbOH), the starting material for most rubidium-based chemical processes; [[rubidium carbonate]] (Rb<sub>2</sub>CO<sub>3</sub>), used in some optical glasses, and rubidium copper sulfate, Rb<sub>2</sub>SO<sub>4</sub>·CuSO<sub>4</sub>·6H<sub>2</sub>O. [[Rubidium silver iodide]] (RbAg<sub>4</sub>I<sub>5</sub>) has the highest [[room temperature]] [[electrical conductivity|conductivity]] of any known [[ionic crystal]], a property exploited in thin film [[battery (electricity)|batteries]] and other applications.<ref>{{Cite book |chapter-url = https://books.google.com/books?id=pVw98i6gtwMC&pg=PA176 |title = Solid state chemistry: an introduction |chapter = RbAg<sub>4</sub>I<sub>5</sub> |first = Lesley |last = Smart |author2 = Moore, Elaine |publisher = CRC Press |date = 1995 |isbn = 978-0-7487-4068-0 |pages = [https://archive.org/details/solidstatechemis00smar_0/page/176 176–177] |url-access = registration |url = https://archive.org/details/solidstatechemis00smar_0/page/176 }}</ref><ref>{{Cite journal |title = Relationship of structure and ionic mobility in solid MAg<sub>4</sub>I<sub>5</sub> |first = J. N. |last = Bradley |author2=Greene, P. D. |journal = Trans. Faraday Soc. |date = 1967 |volume = 63 |pages = 2516 |doi = 10.1039/TF9676302516}}</ref>

Rubidium forms a number of [[Rubidium oxide|oxides]] when exposed to air, including rubidium monoxide (Rb<sub>2</sub>O), Rb<sub>6</sub>O, and Rb<sub>9</sub>O<sub>2</sub>; rubidium in excess oxygen gives the [[superoxide]] [[Rubidium superoxide|RbO<sub>2</sub>]]. Rubidium forms salts with halogens, producing [[rubidium fluoride]], [[rubidium chloride]], [[rubidium bromide]], and [[rubidium iodide]].<ref name=G&W>{{Greenwood&Earnshaw2nd}}</ref>

===Isotopes===
{{Main|Isotopes of rubidium}}
Rubidium in the Earth's crust is composed of two isotopes: the stable <sup>85</sup>Rb (72.2%) and the [[radioactive]] <sup>87</sup>Rb (27.8%).<ref name="Audi">{{NUBASE 2003}}</ref> Natural rubidium is radioactive, with specific activity of about 670 [[Becquerel|Bq]]/g, enough to significantly expose a [[photographic film]] in 110 days.<ref>{{cite journal | last1 = Strong | first1 = W. W. | title = On the Possible Radioactivity of Erbium, Potassium and Rubidium | journal = Physical Review | series = Series I | volume = 29 | issue = 2 | pages = 170–173 | date = 1909 | doi = 10.1103/PhysRevSeriesI.29.170 |bibcode = 1909PhRvI..29..170S | url = https://zenodo.org/record/1545957 }}</ref><ref>{{cite book | url = https://books.google.com/books?id=6khCAQAAIAAJ | pages = 4–25 | title = CRC handbook of chemistry and physics: a ready-reference book of chemical and physical data | isbn = 978-0-8493-0476-7 | author1 = Lide, David R | author2 = Frederikse, H. P. R | date = June 1995| publisher = CRC-Press }}</ref> <!--CRC rubber bible gives 30 to 60 days but I could not find a source in science literature.-->Thirty additional rubidium isotopes have been synthesized with half-lives of less than 3&nbsp;months; most are highly radioactive and have few uses.<ref>{{cite web |url=http://www.nucleonica.net/unc.aspx |title=Universal Nuclide Chart |publisher=nucleonica |url-access=registration|accessdate=2017-01-03 |archive-date=2017-02-19 |archive-url=https://web.archive.org/web/20170219043412/http://www.nucleonica.net/unc.aspx |url-status=live }}</ref>

Rubidium-87 has a [[half-life]] of {{val|48.8|e=9}}&nbsp;years, which is more than three times the [[age of the universe]] of {{val|13.799|0.021|e=9}}&nbsp;years,<ref name="Planck 2015">{{cite journal
 |author=Planck Collaboration
 |year=2016
 |title=Planck 2015 results. XIII. Cosmological parameters (See Table 4 on page 31 of pfd).
 |arxiv=1502.01589
|doi=10.1051/0004-6361/201525830
 |bibcode=2016A&A...594A..13P
 |volume=594
 |journal=Astronomy & Astrophysics
 |page=A13
 |s2cid=119262962
 }}</ref> making it a [[primordial nuclide]]. It readily substitutes for [[potassium]] in [[mineral]]s, and is therefore fairly widespread. Rb has been used extensively in [[rock dating|dating rocks]]; <sup>87</sup>Rb [[beta decay]]s to stable <sup>87</sup>Sr. During [[Fractional crystallization (geology)|fractional crystallization]], Sr tends to concentrate in [[plagioclase]], leaving Rb in the liquid phase. Hence, the Rb/Sr ratio in residual [[magma]] may increase over time, and the progressing [[Igneous differentiation|differentiation]] results in rocks with elevated Rb/Sr ratios. The highest ratios (10 or more) occur in [[pegmatite]]s. If the initial amount of Sr is known or can be extrapolated, then the age can be determined by measurement of the Rb and Sr concentrations and of the <sup>87</sup>Sr/<sup>86</sup>Sr ratio. The dates indicate the true age of the minerals only if the rocks have not been subsequently altered (see [[rubidium–strontium dating]]<!-- the hyphen is correct, it uses Rb/Rb and Sr/Sr ratios -->).<ref>{{Cite book |chapter-url = https://books.google.com/books?id=k90iAnFereYC&pg=PA162 |chapter = Rubidium-Strontium Dating |title = Isotopes in the Earth Sciences |first1 = H.-G. |last1 = Attendorn |first2 = Robert |last2 = Bowen |publisher = Springer |date = 1988 |isbn = 978-0-412-53710-3| pages = 162–165}}</ref><ref>{{Cite book |chapter-url =https://books.google.com/books?id=cYWNAZbPhMYC&pg=PA383 |title = Essentials of geochemistry |first1 =John Victor |last1 =Walther |publisher =Jones & Bartlett Learning|orig-year=1988 | date = 2009 |isbn =978-0-7637-5922-3| chapter =Rubidium-Strontium Systematics| pages = 383–385}}</ref>

[[Rubidium-82]], one of the element's non-natural isotopes, is produced by [[electron capture|electron-capture]] decay of [[strontium-82]] with a half-life of 25.36&nbsp;days. With a half-life of 76 seconds, rubidium-82 decays by positron emission to stable [[krypton-82]].<ref name="Audi" />