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Francium
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{{Short description|Chemical element}} {{pp-vand|small=yes}} {{Use mdy dates|date=May 2022|cs1-dates=l}} {{Infobox francium}} '''Francium''' is a [[chemical element]]; it has [[chemical symbol|symbol]] '''Fr''' and [[atomic number]] 87. It is extremely [[radioactive]]; its most stable isotope, francium-223 (originally called ''[[actinium]] K'' after the natural [[decay chain]] in which it appears), has a [[half-life]] of only 22 minutes. It is the second-most [[electronegative|electropositive]] element, behind only [[caesium]],<!--PLEASE DO NOT CHANGE THIS; IT IS CORRECT. SEE BELOW. FRANCIUM IS VERY HEAVY, SO THE 7S ELECTRON MOVES SO FAST THAT YOU MUST CONSIDER RELATIVITY! THE EFFECT IS A STABILIZATION OF THE 7S ORBITAL, ENOUGH TO BRING THE ELECTRONEGATIVITY UP ABOVE CAESIUM'S!--> and is the [[Abundance of the chemical elements|second rarest]] naturally occurring element (after [[astatine]]). Francium's isotopes decay quickly into astatine, [[radium]], and [[radon]]. The [[electronic structure]] of a francium atom is [Rn] 7s<sup>1</sup>; thus, the element is classed as an [[alkali metal]]. As a consequence of its extreme instability, bulk francium has never been seen. Because of the general appearance of the other elements in its periodic table column, it is presumed that francium would appear as a highly reactive metal if enough could be collected together to be viewed as a bulk solid or liquid. Obtaining such a sample is highly improbable since the extreme heat of decay resulting from its short half-life would immediately vaporize any viewable quantity of the element. Francium was discovered by [[Marguerite Perey]]<ref>{{Cite web |last=Guruge |first=Amila Ruwan |date=2023-01-25 |title=Francium |url=https://www.arhse.com/francium/ |access-date=2023-02-28 |website=Chemical and Process Engineering |language=en-US}}</ref> in France (from which the element takes its name) on January 7, 1939.<ref>{{cite journal |last=Perey |first=M. |date=October 1, 1939 |title = L'élément 87 : AcK, dérivé de l'actinium |journal=Journal de Physique et le Radium |language=fr |volume=10 |issue=10 |pages=435–438 |doi=10.1051/jphysrad:019390010010043500 |issn=0368-3842 |url=https://hal.archives-ouvertes.fr/jpa-00233698/document}}</ref> Before its discovery, francium was referred to as ''[[Mendeleev's predicted elements|eka]]-[[caesium]]'' or ''ekacaesium'' because of its conjectured existence below caesium in the periodic table. It was the last element first discovered in nature, rather than by synthesis.{{NoteTag|Some synthetic elements, like [[technetium]] and [[plutonium]], have later been found in nature.}} Outside the laboratory, francium is extremely rare, with trace amounts found in [[uranium]] ores, where the [[isotope]] francium-223 (in the family of uranium-235) continually forms and decays. As little as {{convert|1|oz|g}} exists at any given time throughout the [[Earth's crust]]; aside from francium-223 and francium-221, its other isotopes are entirely synthetic. The largest amount produced in the laboratory was a cluster of more than 300,000 atoms.<ref name="chemnews" />
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