Editing Rubidium (section)

=== 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" />