Editing Francium (section)

==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&nbsp;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&nbsp;seconds, although synthetic astatine-210 is much longer-lived with a half-life of 8.1&nbsp;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&nbsp;[[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&nbsp;g/cm<sup>3</sup> (Mendeleev's method extrapolates 2.4&nbsp;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)&nbsp;kJ/mol as opposed to 375.7041(2)&nbsp;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>