Francium

Francium is a chemical element; it has 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 electropositive element, behind only caesium, and is the 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] 7s¹; 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{{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}} in France (from which the element takes its name) on January 7, 1939.{{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}} Before its discovery, francium was referred to as 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.

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. All isotopes of francium decay into astatine, radium, or radon.{{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}} Francium-223 also has a shorter half-life than the longest-lived isotope known of each element up to and including element 105, dubnium.{{cite book |year =2006 |title = CRC Handbook of Chemistry and Physics |volume = 4 |page= 12 |publisher = CRC |isbn= 978-0-8493-0474-3}}

Francium is an alkali metal whose chemical properties mostly resemble those of caesium. A heavy element with a single valence electron,{{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}} it has the highest equivalent weight of any element. Liquid francium—if created—should have a surface tension of 0.05092 N/m at its melting point.{{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}} Francium's melting point was estimated to be around {{convert|8.0|C|F}};{{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}} a value of {{convert|27|C|F}} is also often encountered. 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}}.{{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=}} 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. The density of francium is expected to be around 2.48 g/cm³ (Mendeleev's method extrapolates 2.4 g/cm³).

{{anchor|electronegativity}}Linus Pauling estimated the electronegativity of francium at 0.7 on the Pauling scale, the same as caesium;{{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}} 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.{{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}} Francium has a slightly higher ionization energy than caesium,{{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}} 392.811(4) kJ/mol as opposed to 375.7041(2) kJ/mol for caesium, as would be expected from 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⁻ ion should be more polarizable than the Cs⁻ ion.{{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}}

Compounds

As a result of francium's instability, its salts are only known to a small extent. Francium coprecipitates with several caesium salts, such as caesium perchlorate, which results in small amounts of francium perchlorate. This coprecipitation can be used to isolate francium, by adapting the radiocaesium coprecipitation method of Lawrence E. Glendenin and C. M. Nelson. It will additionally coprecipitate with many other caesium salts, including the iodate, the picrate, the tartrate (also rubidium tartrate), the chloroplatinate, and the silicotungstate. It also coprecipitates with silicotungstic acid, and with perchloric acid, without another alkali metal as a carrier, which leads to other methods of separation.{{cite journal |last= Hyde |first= E. K. |title= Radiochemical Methods for the Isolation of Element 87 (Francium) |journal= J. Am. Chem. Soc. |date= 1952 |volume= 74 |issue= 16 |pages= 4181–4184 |doi= 10.1021/ja01136a066|bibcode= 1952JAChS..74.4181H |hdl= 2027/mdp.39015086483156 |s2cid= 95854270 |hdl-access= free}}E. N K. Hyde Radiochemistry of Francium, Subcommittee on Radiochemistry, National Academy of Sciences-National Research Council; available from the Office of Technical Services, Dept. of Commerce, 1960.

=Francium perchlorate=

Francium perchlorate is produced by the reaction of francium chloride and sodium perchlorate. The francium perchlorate coprecipitates with caesium perchlorate. This coprecipitation can be used to isolate francium, by adapting the radiocaesium coprecipitation method of Lawrence E. Glendenin and C. M. Nelson. However, this method is unreliable in separating thallium, which also coprecipitates with caesium. Francium perchlorate's entropy is expected to be 42.7 e.u (178.7 J mol⁻¹ K⁻¹).

=Francium halides=

Francium halides are all soluble in water and are expected to be white solids. They are expected to be produced by the reaction of the corresponding halogens. For example, francium chloride would be produced by the reaction of francium and chlorine. Francium chloride has been studied as a pathway to separate francium from other elements, by using the high vapour pressure of the compound, although francium fluoride would have a higher vapour pressure.

=Other compounds=

Francium nitrate, sulfate, hydroxide, carbonate, acetate, and oxalate, are all soluble in water, while the iodate, picrate, tartrate, 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. Francium oxide is believed to disproportionate to the peroxide and francium metal.{{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}} The CsFr molecule is predicted to have the heavier element (francium) at the negative end of the dipole, unlike all known heterodiatomic alkali metal molecules. Francium superoxide (FrO₂) is expected to have a more covalent character than its lighter congeners; this is attributed to the 6p electrons in francium being more involved in the francium–oxygen bonding. The relativistic destabilisation of the 6p_3/2 spinor may make francium compounds in oxidation states higher than +1 possible, such as [Fr^VF₆]⁻; but this has not been experimentally confirmed.{{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|doi-access=free }}

Isotopes

There are 37 known isotopes of francium ranging in atomic mass from 197 to 233.{{NUBASE2020|ref}} Francium has seven metastable nuclear isomers. Francium-223 and francium-221 are the only isotopes that occur in nature, with the former being far more common.{{cite book|date = 2005|title= Francium, in Van Nostrand's Encyclopedia of Chemistry|editor-last = Considine| editor-first = Glenn D.| page= 679|location= New York| publisher = Wiley-Interscience| isbn = 978-0-471-61525-5}}

Francium-223 is the most stable isotope, with a half-life of 21.8 minutes, and it is highly unlikely that an isotope of francium with a longer half-life will ever be discovered or synthesized. Francium-223 is a fifth product of the uranium-235 decay series as a daughter isotope of actinium-227; thorium-227 is the more common daughter.{{cite book|date = 2005|title= Chemical Elements, in Van Nostrand's Encyclopedia of Chemistry|editor-last = Considine| editor-first = Glenn D.|page=332|location= New York| publisher = Wiley-Interscience| isbn = 978-0-471-61525-5}} Francium-223 then decays into radium-223 by beta decay (1.149 MeV decay energy), with a minor (0.006%) alpha decay path to astatine-219 (5.4 MeV decay energy).{{cite web |author=National Nuclear Data Center |date=1990 |title=Table of Isotopes decay data |url=http://ie.lbl.gov/toi/nuclide.asp?iZA=870223 |publisher=Brookhaven National Laboratory |access-date=April 4, 2007 |url-status=dead |archive-url=https://web.archive.org/web/20061031212436/http://ie.lbl.gov/toi/nuclide.asp?iZA=870223 |archive-date=October 31, 2006}}

Francium-221 has a half-life of 4.8 minutes. It is the ninth product of the neptunium decay series as a daughter isotope of actinium-225. Francium-221 then decays into astatine-217 by alpha decay (6.457 MeV decay energy). Although all primordial ²³⁷Np is extinct, the neptunium decay series continues to exist naturally in tiny traces due to (n,2n) knockout reactions in natural ²³⁸U.{{cite journal |last1=Peppard |first1=D. F. |last2=Mason |first2=G. W. |last3=Gray |first3=P. R. |last4=Mech |first4=J. F. |title=Occurrence of the (4n + 1) series in nature |journal=Journal of the American Chemical Society |date=1952 |volume=74 |issue=23 |pages=6081–6084 |doi=10.1021/ja01143a074 |bibcode=1952JAChS..74.6081P |url=https://digital.library.unt.edu/ark:/67531/metadc172698/m2/1/high_res_d/metadc172698.pdf }} Francium-222, with a half-life of 14 minutes, may be produced as a result of the beta decay of natural radon-222; this process has nonetheless not yet been observed,{{cite journal |last1=Belli |first1=P. |last2=Bernabei |first2=R. |last3=Danevich |first3=F. A. |last4=Incicchitti |first4=A. |last5=Tretyak |first5=V. I. |display-authors=3 |title=Experimental searches for rare alpha and beta decays |journal=European Physical Journal A |date=2019 |volume=55 |issue=8 |pages=140–1–140–7 |doi=10.1140/epja/i2019-12823-2 |issn=1434-601X |arxiv=1908.11458|bibcode=2019EPJA...55..140B |s2cid=201664098 }} and it is unknown whether this process is energetically possible.{{NoteTag|AME2020 gives ²²²Rn a lower mass than ²²²Fr,{{AME2020 II|ref}} which would forbid single beta decay, though it is possible within the given error margin and is explicitly predicted by Belli et al.{{cite journal |last1=Belli |first1=P. |last2=Bernabei |first2=R. |last3=Cappella |first3=C. |last4=Caracciolo |first4=V. |last5=Cerulli |first5=R. |last6=Danevich |first6=F.A. |last7=Di Marco |first7=A. |last8=Incicchitti |first8=A. |last9=Poda |first9=D.V. |last10=Polischuk |first10=O.G. |last11=Tretyak |first11=V.I. |title=Investigation of rare nuclear decays with BaF₂ crystal scintillator contaminated by radium |date=2014 |journal=European Physical Journal A |volume=50 |issue=9 |pages=134–143 |doi=10.1140/epja/i2014-14134-6 |arxiv=1407.5844|bibcode=2014EPJA...50..134B |s2cid=118513731 }}}}

The least stable ground state isotope is francium-215, with a half-life of 90 ns:{{NUBASE2020|ref}} it undergoes a 9.54 MeV alpha decay to astatine-211.

Applications

Due to its instability and rarity, there are no commercial applications for francium.{{cite web| last = Winter| first = Mark| title = Uses| work = Francium| publisher = The University of Sheffield|url = http://www.webelements.com/webelements/elements/text/Fr/uses.html| access-date = March 25, 2007}}{{cite book| last = Emsley|url=https://books.google.com/books?id=Yhi5X7OwuGkC&pg=PA151| first = John| title = Nature's Building Blocks| publisher = Oxford University Press| date = 2001| location = Oxford| pages = 151–153| isbn = 978-0-19-850341-5}}{{cite web| last = Gagnon| first = Steve| title = Francium| publisher = Jefferson Science Associates, LLC| url = http://education.jlab.org/itselemental/ele087.html | access-date = April 1, 2007}} It has been used for research purposes in the fields of chemistry{{cite journal | last1 = Haverlock |first1 = T. J. |pmid = 12553788 |doi= 10.1021/ja0255251|title = Selectivity of calix[4]arene-bis(benzocrown-6) in the complexation and transport of francium ion |journal = J Am Chem Soc|date = 2003|volume=125|pages=1126–7| last2 = Mirzadeh| first2 = S.|last3 = Moyer| first3 = B. A.|issue = 5|bibcode = 2003JAChS.125.1126H }}

and of atomic structure. Its use as a potential diagnostic aid for various cancers has also been explored, but this application has been deemed impractical.

Francium's ability to be synthesized, trapped, and cooled, along with its relatively simple atomic structure, has made it the subject of specialized spectroscopy experiments. These experiments have led to more specific information regarding energy levels and the coupling constants between subatomic particles.{{cite journal| last = Gomez| first = E.|author2=Orozco, L A |author3=Sprouse, G D | s2cid = 15917603| title = Spectroscopy with trapped francium: advances and perspectives for weak interaction studies| journal = Rep. Prog. Phys.| volume = 69| issue = 1| pages = 79–118| date = November 7, 2005|doi = 10.1088/0034-4885/69/1/R02|bibcode = 2006RPPh...69...79G}} Studies on the light emitted by laser-trapped francium-210 ions have provided accurate data on transitions between atomic energy levels which are fairly similar to those predicted by quantum theory.{{cite journal|last = Peterson|first = I.|title = Creating, cooling, trapping francium atoms|journal = Science News|date = May 11, 1996|url = http://www.sciencenews.org/pages/pdfs/data/1996/149-19/14919-06.pdf|access-date = September 11, 2001|volume = 149|issue = 19|pages = 294|doi = 10.2307/3979560|jstor = 3979560|archive-date = July 27, 2020|archive-url = https://web.archive.org/web/20200727014700/https://www.sciencenews.org/pages/pdfs/data/1996/149-19/14919-06.pdf|url-status = dead}} Francium is a prospective candidate for searching for CP violation.{{cite journal | last1=Osika | first1=Yuliya | last2=Meniailava | first2=Darya | last3=Shundalau | first3=Maksim | title=Relativistic coupled cluster study on the spectroscopic and radiative properties of the KFr molecule and modeling of the transport properties of potassium–francium dilute gas medium | journal=Journal of Quantitative Spectroscopy and Radiative Transfer | publisher=Elsevier BV | volume=321 | year=2024 | issn=0022-4073 | doi=10.1016/j.jqsrt.2024.108996 | page=108996| bibcode=2024JQSRT.32108996O }}

History

As early as 1870, chemists thought that there should be an alkali metal beyond caesium, with an atomic number of 87. It was then referred to by the provisional name eka-caesium.Adloff, Jean-Pierre; Kaufman, George B. (September 25, 2005). [http://chemeducator.org/sbibs/s0010005/spapers/1050387gk.htm Francium (Atomic Number 87), the Last Discovered Natural Element] {{Webarchive|url=https://web.archive.org/web/20130604212956/http://chemeducator.org/sbibs/s0010005/spapers/1050387gk.htm |date=June 4, 2013}} . The Chemical Educator 10 (5). Retrieved on March 26, 2007.

=Erroneous and incomplete discoveries=

In 1914, Stefan Meyer, Viktor F. Hess, and Friedrich Paneth (working in Vienna) made measurements of alpha radiation from various substances, including ²²⁷Ac. They observed the possibility of a minor alpha branch of this nuclide, though follow-up work could not be done due to the outbreak of World War I. Their observations were not precise and sure enough for them to announce the discovery of element 87, though it is likely that they did indeed observe the decay of ²²⁷Ac to ²²³Fr.

Soviet chemist Dmitry Dobroserdov was the first scientist to claim to have found eka-caesium, or francium. In 1925, he observed weak radioactivity in a sample of potassium, another alkali metal, and incorrectly concluded that eka-caesium was contaminating the sample (the radioactivity from the sample was from the naturally occurring potassium radioisotope, potassium-40).{{cite conference| first = Marco| last = Fontani |author-link= Marco Fontani | title = The Twilight of the Naturally-Occurring Elements: Moldavium (Ml), Sequanium (Sq) and Dor (Do)| book-title = International Conference on the History of Chemistry| pages = 1–8| date = September 10, 2005| location = Lisbon|url = http://5ichc-portugal.ulusofona.pt/uploads/PaperLong-MarcoFontani.doc| archive-url = https://web.archive.org/web/20060224090117/http://5ichc-portugal.ulusofona.pt/uploads/PaperLong-MarcoFontani.doc|archive-date=February 24, 2006|access-date = April 8, 2007}} He then published a thesis on his predictions of the properties of eka-caesium, in which he named the element russium after his home country.{{cite web| last = Van der Krogt| first = Peter| title = Francium| work = Elementymology & Elements Multidict| date = January 10, 2006| url = http://elements.vanderkrogt.net/element.php?sym=Fr| access-date = April 8, 2007}} Shortly thereafter, Dobroserdov began to focus on his teaching career at the Polytechnic Institute of Odesa, and he did not pursue the element further.

The following year, English chemists Gerald J. F. Druce and Frederick H. Loring analyzed X-ray photographs of manganese(II) sulfate. They observed spectral lines which they presumed to be of eka-caesium. They announced their discovery of element 87 and proposed the name alkalinium, as it would be the heaviest alkali metal.

In 1930, Fred Allison of the Alabama Polytechnic Institute claimed to have discovered element 87 (in addition to 85) when analyzing pollucite and lepidolite using his magneto-optical machine. Allison requested that it be named virginium after his home state of Virginia, along with the symbols Vi and Vm.{{cite magazine| title = Alabamine & Virginium| magazine = Time | date = February 15, 1932|url = http://www.time.com/time/magazine/article/0,9171,743159,00.html|archive-url = https://web.archive.org/web/20070930015028/http://www.time.com/time/magazine/article/0,9171,743159,00.html|url-status = dead|archive-date = September 30, 2007| access-date = April 1, 2007}} In 1934, H.G. MacPherson of UC Berkeley disproved the effectiveness of Allison's device and the validity of his discovery.{{cite journal| last = MacPherson| first = H. G.| title = An Investigation of the Magneto-Optic Method of Chemical Analysis| journal = Physical Review| volume = 47| issue = 4| pages = 310–315|date=1934|doi = 10.1103/PhysRev.47.310|bibcode = 1935PhRv...47..310M}}

In 1936, Romanian physicist Horia Hulubei and his French colleague Yvette Cauchois also analyzed pollucite, this time using their high-resolution X-ray apparatus. They observed several weak emission lines, which they presumed to be those of element 87. Hulubei and Cauchois reported their discovery and proposed the name moldavium, along with the symbol Ml, after Moldavia, the Romanian province where Hulubei was born. In 1937, Hulubei's work was criticized by American physicist F. H. Hirsh Jr., who rejected Hulubei's research methods. Hirsh was certain that eka-caesium would not be found in nature, and that Hulubei had instead observed mercury or bismuth X-ray lines. Hulubei insisted that his X-ray apparatus and methods were too accurate to make such a mistake. Because of this, Jean Baptiste Perrin, Nobel Prize winner and Hulubei's mentor, endorsed moldavium as the true eka-caesium over Marguerite Perey's recently discovered francium. Perey took pains to be accurate and detailed in her criticism of Hulubei's work, and finally she was credited as the sole discoverer of element 87. All other previous purported discoveries of element 87 were ruled out due to francium's very limited half-life.

=Perey's analysis=

Eka-caesium was discovered on January 7, 1939, by Marguerite Perey of the Curie Institute in Paris, when she purified a sample of actinium-227 which had been reported to have a decay energy of 220 keV. Perey noticed decay particles with an energy level below 80 keV. Perey thought this decay activity might have been caused by a previously unidentified decay product, one which was separated during purification, but emerged again out of the pure actinium-227. Various tests eliminated the possibility of the unknown element being thorium, radium, lead, bismuth, or thallium. The new product exhibited chemical properties of an alkali metal (such as coprecipitating with caesium salts), which led Perey to believe that it was element 87, produced by the alpha decay of actinium-227. Perey then attempted to determine the proportion of beta decay to alpha decay in actinium-227. Her first test put the alpha branching at 0.6%, a figure which she later revised to 1%.

Perey named the new isotope actinium-K (it is now referred to as francium-223) and in 1946, she proposed the name catium (Cm) for her newly discovered element, as she believed it to be the most electropositive cation of the elements. Irène Joliot-Curie, one of Perey's supervisors, opposed the name due to its connotation of cat rather than cation; furthermore, the symbol coincided with that which had since been assigned to curium. Perey then suggested francium, after France. This name was officially adopted by the International Union of Pure and Applied Chemistry (IUPAC) in 1949, becoming the second element after gallium to be named after France. It was assigned the symbol Fa, but it was revised to the current Fr shortly thereafter.{{Cite book| last = Grant| first = Julius| contribution = Francium| date = 1969| title = Hackh's Chemical Dictionary| pages = 279–280| publisher = McGraw-Hill| isbn = 978-0-07-024067-4}} Francium was the last element discovered in nature, rather than synthesized, following hafnium and rhenium. Further research into francium's structure was carried out by, among others, Sylvain Lieberman and his team at CERN in the 1970s and 1980s.{{cite web

|title = History

|work = Francium

|publisher = State University of New York at Stony Brook

|date = February 20, 2007

|url = http://fr.physics.sunysb.edu/francium_news/history.HTM

|access-date = March 26, 2007

|url-status = dead

|archive-url = https://archive.today/19990203121919/http://fr.physics.sunysb.edu/francium_news/history.HTM

|archive-date = February 3, 1999

|df = mdy-all

}}

Occurrence

File:Pichblende.jpg contains about 100,000 atoms (3.7{{e|-17}} g) of francium-223 at any given time.|alt=A shiny gray 5-centimeter piece of matter with a rough surface.]]

²²³Fr is the result of the alpha decay of ²²⁷Ac and can be found in trace amounts in uranium minerals. In a given sample of uranium, there is estimated to be only one francium atom for every 1 × 10¹⁸ uranium atoms. Only about {{convert|1|oz|g}} of francium is present naturally in the earth's crust.{{Cite book |last=Krebs |first=Robert E. |url=https://books.google.com/books?id=D7LOEAAAQBAJ&dq=%22francium%20hydroxide%22%20existence&pg=PA64 |title=The History and Use of Our Earth's Chemical Elements: A Reference Guide |date=2006-07-30 |publisher=Bloomsbury Publishing USA |isbn=978-0-313-02798-7 |language=en}}

Production

File:franciumtrap.PNG, which can hold neutral francium atoms for short periods of time.|alt=A complex experimental setup featuring a horizontal glass tube placed between two copper coils.]]

Francium can be synthesized by a 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.{{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}} Depending on the energy of the oxygen beam, the reaction can yield francium isotopes with masses of 209, 210, and 211.

:¹⁹⁷Au + ¹⁸O → ²⁰⁹Fr + 6 n

:¹⁹⁷Au + ¹⁸O → ²¹⁰Fr + 5 n

:¹⁹⁷Au + ¹⁸O → ²¹¹Fr + 4 n

{{multiple image

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| image1 = Francium (200,000 francium atoms in a magneto-optical trap).jpg

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| alt1 = A round ball of red light surrounded by a green glow

| caption1 = Image of light emitted by a sample of 200,000 francium atoms in a magneto-optical trap

| image2 = Fr,87.jpg

| width2 = 150

| alt2 = A small white spot in the middle surrounded by a red circle. There is a yellow ring outside the red circle, a green circle beyond the yellow ring and a blue circle surrounding all the other circles.

| caption2 = Heat image of 200,000 francium atoms in a magneto-optical trap, around 100 attograms

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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 magneto-optical trap (MOT) in a gaseous unconsolidated state.{{cite web| title = Cooling and Trapping| work = Francium| publisher = State University of New York at Stony Brook| date = February 20, 2007| url = http://fr.physics.sunysb.edu/francium_news/trapping.HTM| access-date = May 1, 2007| url-status = dead| archive-url = https://archive.today/20071122170110/http://fr.physics.sunysb.edu/francium_news/trapping.HTM| archive-date = November 22, 2007}} Although the atoms only remain in the trap for about 30 seconds before escaping or undergoing nuclear decay, the process supplies a continual stream of fresh atoms. The result is a steady state containing a fairly constant number of atoms for a much longer time. The original apparatus could trap up to a few thousand atoms, while a later improved design could trap over 300,000 at a time.{{cite journal|url=http://pubs.acs.org/cen/80th/francium.html|title=Francium|journal=Chemical and Engineering News|date=2003|first=Luis A. |last=Orozco |volume=81|issue=36|pages=159|doi=10.1021/cen-v081n036.p159|url-access=subscription}} Sensitive measurements of the light emitted and absorbed by the trapped atoms provided the first experimental results on various transitions between atomic energy levels in francium. Initial measurements show very good agreement between experimental values and calculations based on quantum theory. The research project using this production method relocated to TRIUMF in 2012, where over 10⁶ francium atoms have been held at a time, including large amounts of ²⁰⁹Fr in addition to ²⁰⁷Fr and ²²¹Fr.{{cite report |url= https://www.osti.gov/servlets/purl/1214938 |title= Project Closeout Report: Francium Trapping Facility at TRIUMF |publisher= U.S. Department of Energy |date= September 30, 2014 |doi= 10.2172/1214938 |last1= Orozco |first1= Luis A.}}{{cite journal |journal= Journal of Instrumentation |title= Commissioning of the Francium Trapping Facility at TRIUMF |first1= M |last1= Tandecki |first2= J. |last2= Zhang |first3= R. |last3= Collister |first4= S. |last4= Aubin |first5= J. A. |last5= Behr |first6= E. |last6= Gomez |first7= G. |last7= Gwinner |first8= L. A. |last8= Orozco |first9= M. R. |last9= Pearson |s2cid= 15501597 |volume= 8 |issue= 12 |pages= 12006 |year= 2013 |doi= 10.1088/1748-0221/8/12/P12006 |arxiv= 1312.3562 |bibcode= 2013JInst...8P2006T}}

Other synthesis methods include bombarding radium with neutrons, and bombarding thorium with protons, deuterons, or helium ions.{{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}}

²²³Fr can also be isolated from samples of its parent ²²⁷Ac, the francium being milked via elution with NH₄Cl–CrO₃ from an actinium-containing cation exchanger and purified by passing the solution through a silicon dioxide compound loaded with barium sulfate.{{Ullmann | first1=Cornelius |last1=Keller |first2=Walter |last2=Wolf |first3=Jashovam |last3=Shani | title = Radionuclides, 2. Radioactive Elements and Artificial Radionuclides | doi = 10.1002/14356007.o22_o15}}

In 1996, the Stony Brook group trapped 3000 atoms in their MOT, which was enough for a video camera to capture the light given off by the atoms as they fluoresce. Francium has not been synthesized in amounts large enough to weigh.{{cite web | title = Francium |publisher = Los Alamos National Laboratory |year = 2011 |url = http://periodic.lanl.gov/87.shtml |access-date = February 19, 2012}}

Notes

References

External links

[http://www.periodicvideos.com/videos/087.htm Francium] at The Periodic Table of Videos (University of Nottingham)
[http://www.webelements.com/webelements/elements/text/Fr/index.html WebElements.com – Francium]
[https://web.archive.org/web/19981203125538/http://fr.physics.sunysb.edu/francium_news/frconten.htm Stony Brook University Physics Dept.]
Scerri, Eric (2013). A Tale of Seven Elements, Oxford University Press, Oxford, {{ISBN|9780195391312}}