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{{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.<ref>{{Cite web |title=Francium (Fr) {{!}} AMERICAN ELEMENTS ® |url=https://www.americanelements.com/francium.html |access-date=2024-05-02 |website=American Elements: The Materials Science Company |language=en}}</ref> 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
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 is an alkali metal whose chemical properties mostly resemble those of caesium.<ref name="CRC2006" /> A heavy element with a single [[valence electron]],<ref>{{cite web| last = Winter| first = Mark| title = Electron Configuration| work = Francium| publisher = The University of Sheffield| url = http://www.webelements.com/webelements/elements/text/Fr/eneg.html| access-date = April 18, 2007}}</ref> it has the highest [[equivalent weight]] of any element.<ref name="CRC2006" /> Liquid francium—if created—should have a [[surface tension]] of 0.05092 [[newton (unit)|N]]/m at its melting point.<ref name="Kozhitov">{{cite journal |last1 = Kozhitov| first1 = L. V.| last2=Kol'tsov|first2=V. B. |last3=Kol'tsov|first3=A. V.| s2cid = 97764887| title = Evaluation of the Surface Tension of Liquid Francium|journal = Inorganic Materials | volume = 39| issue = 11 |pages = 1138–1141 |year = 2003 |doi = 10.1023/A:1027389223381}}</ref> Francium's melting point was estimated to be around {{convert|8.0|C|F}};<ref name="L&P" /> a value of {{convert|27|C|F}} is also often encountered.<ref name="CRC2006" /> The melting point is uncertain because of the element's extreme rarity and [[radioactivity]]; a different extrapolation based on [[Dmitri Mendeleev]]'s method gave {{convert|20|±|1.5|C|F}}. A calculation based on the melting temperatures of binary ionic crystals gives {{convert|24.861|±|0.517|C|F}}.<ref>{{cite journal |last=Oshchapovskii |first=V. V. |date=2014 |title =A New Method of Calculation of the Melting Temperatures of Crystals of Group 1A Metal Halides and Francium Metal |journal=Russian Journal of Inorganic Chemistry |language=en |volume=59 |issue=6 |pages=561–567 |doi=10.1134/S0036023614060163 |s2cid=98622837 |issn= |url=}}</ref> The estimated boiling point of {{convert|620|C|F}} is also uncertain; the estimates {{convert|598|C|F}} and {{convert|677|C|F}}, as well as the extrapolation from Mendeleev's method of {{convert|640|C|F}}, have also been suggested.<ref name="L&P" /><ref name="Kozhitov" /> The density of francium is expected to be around 2.48 g/cm<sup>3</sup> (Mendeleev's method extrapolates 2.4 g/cm<sup>3</sup>).<ref name="L&P" />▼
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" />
==Characteristics==
Francium is one of the most unstable of the naturally occurring elements: its longest-lived isotope, francium-223, has a [[half-life]] of only 22 minutes. The only comparable element is [[astatine]], whose most stable natural isotope, astatine-219 (the alpha daughter of francium-223), has a half-life of 56 seconds, although synthetic astatine-210 is much longer-lived with a half-life of 8.1 hours.<ref name="andyscouse" /> All isotopes of francium decay into astatine, [[radium]], or [[radon]].<ref name="andyscouse">{{cite web | last = Price | first = Andy| title = Francium | date = December 20, 2004| url = http://www.andyscouse.com/pages/francium.htm | access-date = February 19, 2012}}</ref> Francium-223 also has a shorter half-life than the longest-lived isotope of each synthetic element up to and including element 105, [[dubnium]].<ref name="CRC2006">{{cite book |year =2006 |title = CRC Handbook of Chemistry and Physics |volume = 4 |page= 12 |publisher = CRC |isbn= 978-0-8493-0474-3}}</ref>
▲Francium is an alkali metal whose chemical properties mostly resemble those of caesium.<ref name="CRC2006" /> A heavy element with a single [[valence electron]],<ref>{{cite web| last = Winter| first = Mark| title = Electron Configuration| work = Francium| publisher = The University of Sheffield| url = http://www.webelements.com/webelements/elements/text/Fr/eneg.html| access-date = April 18, 2007}}</ref> it has the highest [[equivalent weight]] of any element.<ref name="CRC2006" /> Liquid francium—if created—should have a [[surface tension]] of 0.05092 [[newton (unit)|N]]/m at its melting point.<ref name="Kozhitov">{{cite journal |last1 = Kozhitov| first1 = L. V.| last2=Kol'tsov|first2=V. B. |last3=Kol'tsov|first3=A. V.| s2cid = 97764887| title = Evaluation of the Surface Tension of Liquid Francium|journal = Inorganic Materials | volume = 39| issue = 11 |pages = 1138–1141 |year = 2003 |doi = 10.1023/A:1027389223381}}</ref> Francium's melting point was estimated to be around {{convert|8.0|C|F}};<ref name="L&P">{{cite book |title=Analytical Chemistry of Technetium, Promethium, Astatine, and Francium |first1=Avgusta Konstantinovna |last1=Lavrukhina |first2=Aleksandr Aleksandrovich |last2=Pozdnyakov |year=1970 |publisher=Ann Arbor–Humphrey Science Publishers |others=Translated by R. Kondor |isbn=978-0-250-39923-9 |page=269}}</ref> a value of {{convert|27|C|F}} is also often encountered.<ref name="CRC2006" /> The melting point is uncertain because of the element's extreme rarity and [[radioactivity]]; a different extrapolation based on [[Dmitri Mendeleev]]'s method gave {{convert|20|±|1.5|C|F}}. A calculation based on the melting temperatures of binary ionic crystals gives {{convert|24.861|±|0.517|C|F}}.<ref>{{cite journal |last=Oshchapovskii |first=V. V. |date=2014 |title =A New Method of Calculation of the Melting Temperatures of Crystals of Group 1A Metal Halides and Francium Metal |journal=Russian Journal of Inorganic Chemistry |language=en |volume=59 |issue=6 |pages=561–567 |doi=10.1134/S0036023614060163 |s2cid=98622837 |issn= |url=}}</ref> The estimated boiling point of {{convert|620|C|F}} is also uncertain; the estimates {{convert|598|C|F}} and {{convert|677|C|F}}, as well as the extrapolation from Mendeleev's method of {{convert|640|C|F}}, have also been suggested.<ref name="L&P" /><ref name="Kozhitov" /> The density of francium is expected to be around 2.48 g/cm<sup>3</sup> (Mendeleev's method extrapolates 2.4 g/cm<sup>3</sup>).<ref name="L&P" />
{{anchor|electronegativity}}[[Linus Pauling]] estimated the [[electronegativity]] of francium at 0.7 on the [[Pauling scale]], the same as caesium;<ref>{{cite book |last = Pauling | first = Linus | title = The Nature of the Chemical Bond |edition = Third | author-link = Linus Pauling |publisher = Cornell University Press |year = 1960 | isbn = 978-0-8014-0333-0 |page = 93}}</ref> the value for caesium has since been refined to 0.79, but there are no experimental data to allow a refinement of the value for francium.<ref>{{cite journal |author = Allred, A. L. |year = 1961 |journal= J. Inorg. Nucl. Chem.|volume= 17 |issue= 3–4 |pages= 215–221 |title= Electronegativity values from thermochemical data |doi= 10.1016/0022-1902(61)80142-5}}</ref> Francium has a slightly higher [[ionization energy]] than caesium,<ref>{{cite journal|author = Andreev, S.V.|author2 = Letokhov, V.S.|author3 = Mishin, V.I.|title = Laser resonance photoionization spectroscopy of Rydberg levels in Fr|journal = [[Physical Review Letters]]|date = 1987|volume = 59|pages = 1274–76|doi = 10.1103/PhysRevLett.59.1274|pmid=10035190|bibcode=1987PhRvL..59.1274A|issue = 12}}</ref> 392.811(4) kJ/mol as opposed to 375.7041(2) kJ/mol for caesium, as would be expected from [[Relativistic quantum chemistry|relativistic effects]], and this would imply that caesium is the less electronegative of the two. Francium should also have a higher [[electron affinity]] than caesium and the Fr<sup>−</sup> ion should be more [[polarizability|polarizable]] than the Cs<sup>−</sup> ion.<ref name="Thayer">{{cite book |last1=Thayer |first1=John S. |title=Relativistic Methods for Chemists|chapter=Chap.10 Relativistic Effects and the Chemistry of the Heavier Main Group Elements |date=2010 |page=81 |isbn=978-1-4020-9975-5 |publisher=Springer |doi=10.1007/978-1-4020-9975-5_2}}</ref>
==Compounds==
As a result of francium's
===Francium perchlorate===
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===Other compounds===
Francium nitrate, sulfate, hydroxide, carbonate, acetate, and oxalate, are all soluble in water, while the [[iodate]], [[picrate]], [[tartrate]], [[Chloroplatinic acid|chloroplatinate]], and [[silicotungstate]] are insoluble. The insolubility of these compounds are used to extract francium from other radioactive products, such as [[zirconium]], [[niobium]], [[molybdenum]], [[tin]], [[antimony]], the method mentioned in the section above.<ref name="L&P" /> Francium oxide is believed to disproportionate to the peroxide and francium metal.<ref>{{cite report|page=9|id=UCRL-409|url=https://escholarship.org/uc/item/8056g18b|title=Low Mass Francium and Emanation Isotopes of High Alpha Stability|first1=E. K.|last1=Hyde|first2=A.|last2=Ghiorso|author-link2=Albert Ghiorso|first3=G. T.|last3=Seaborg|author-link3=Glenn Seaborg|date=10 Oct 1949|location=Berkeley, CA|institution=[[UC Radiation Laboratory]]}}</ref> The CsFr molecule is predicted to have francium at the negative end of the dipole, unlike all known heterodiatomic alkali metal molecules. Francium [[superoxide]] (FrO<sub>2</sub>) is expected to have a more [[covalent]] character than its lighter [[congener (chemistry)|congeners]]; this is attributed to the 6p electrons in francium being more involved in the francium–oxygen bonding.<ref name="Thayer" /> The relativistic destabilisation of the 6p<sub>3/2</sub> spinor may make francium compounds in oxidation states higher than +1 possible, such as [Fr<sup>V</sup>F<sub>6</sub>]<sup>−</sup>; but this has not been experimentally confirmed.<ref>{{cite journal |last1=Cao |first1=Chang-Su |last2=Hu |first2=Han-Shi |last3=Schwarz |first3=W. H. Eugen |last4=Li |first4=Jun |date=2022 |title=Periodic Law of Chemistry Overturns for Superheavy Elements |type=preprint |url=https://chemrxiv.org/engage/chemrxiv/article-details/63730be974b7b6d84cfdda35 |journal=[[ChemRxiv]] |volume= |issue= |pages= |doi=10.26434/chemrxiv-2022-l798p |access-date=16 November 2022}}</ref>
==Isotopes==
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==Production==
[[File:franciumtrap.PNG|thumb|left|A [[magneto-optical trap]], which can hold neutral francium atoms for short periods of time.<ref name="sbtrapping" />|alt=A complex experimental setup featuring a horizontal glass tube placed between two copper coils.]]
Francium can be synthesized by a [[nuclear fusion|fusion]] reaction when a gold-197 target is bombarded with a beam of oxygen-18 atoms from a [[linear accelerator]] in a process originally developed at the physics department of the [[State University of New York at Stony Brook]] in 1995.<ref name="sbproduction">{{cite web| title = Production of Francium| work = Francium| publisher = [[State University of New York at Stony Brook]]| date = February 20, 2007| url = http://fr.physics.sunysb.edu/francium_news/production.HTM| access-date = March 26, 2007| url-status = dead| archive-url = https://archive.today/20071012010344/http://fr.physics.sunysb.edu/francium_news/production.HTM| archive-date = October 12, 2007}}</ref> Depending on the energy of the oxygen beam, the reaction can yield francium isotopes with masses of 209, 210, and 211.
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The francium atoms leave the gold target as ions, which are neutralized by collision with [[yttrium]] and then isolated in a [[
Other synthesis methods include bombarding radium with neutrons, and bombarding thorium with protons, [[deuterium|deuterons]], or [[helium]] [[ion]]s.<ref name="mcgraw">{{Cite book| contribution = Francium| date = 2002| title = McGraw-Hill Encyclopedia of Science & Technology| volume = 7| pages = [https://archive.org/details/mcgrawhillencycl165newy/page/493 493–494]| publisher = McGraw-Hill Professional| isbn = 978-0-07-913665-7| title-link = McGraw-Hill Encyclopedia of Science & Technology}}</ref>
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