Francium


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properties
General
Name , symbol , atomic number Francium, Fr, 87
Element category Alkali metals
Group , period , block 1 , 7 , p
Appearance unknown
CAS number 7440-73-5
Mass fraction of the earth's envelope 1.3 · 10 −18  ppm
Atomic
Atomic mass 223.0197 u
Covalent radius 260 pm
Van der Waals radius 348 pm
Electron configuration [ Rn ] 7 s 1
1. Ionization energy 4th.072 741 0 (11) eV 392.96 kJ / mol
2. Ionization energy 22nd.4 (1.9) eV2 160 kJ / mol
3. Ionization energy 33.5 (1.5 eV)3 230 kJ / mol
4. Ionization energy 39.1 (1.7) eV3 770 kJ / mol
5. Ionization energy 50.0 (1.9) eV4 820 kJ / mol
Physically
Physical state firmly
Melting point 298 K K (25 ° C)
boiling point extrapolated: 950 K (677 ° C)
Heat of evaporation approx. 65 kJ / mol
Heat of fusion approx. 2 kJ mol −1
Chemically
Oxidation states +1
Normal potential approx. −2.92 V (Fr + + e - → Fr)
Electronegativity 0.7 ( Pauling scale )
Isotopes
isotope NH t 1/2 ZA ZE (M eV ) ZP
222 Fr {syn.} 14.2 min β - 2.033 222 ra
223 Fr 100% 21.8 min β - 1.149 223 ra
α 5.430 219 at
For other isotopes see list of isotopes
Hazard and safety information
Radioactive
Radioactive
GHS hazard labeling
no classification available
As far as possible and customary, SI units are used.
Unless otherwise noted, the data given apply to standard conditions .

Francium [ ˈfrantsi̯ʊm ] is a radioactive chemical element with the element symbol Fr and the atomic number 87. The element is a metal , is in the 7th period , 1st  IUPAC group (group of alkali metals ) and thus belongs to the s-block .

Francium has the most unstable isotopes of all elements up to atomic number 104 . Even the longest-lived Francium isotope 223 Fr has a half-life of only 21.8 minutes. Because of this property and the lack of an efficient nuclear reaction to produce francium ( 223 Fr is formed in 1% when 227 Ac decays ), it cannot be produced in large quantities. Francium can only be studied as salt in dilute solutions and highly diluted as an amalgam .

Experiments show that francium is a typical alkali metal and is very similar to its lighter homologue cesium . So it is positively monovalent in aqueous solution and can be converted to cesium in the form of sparingly soluble salts, e.g. B. as perchlorate , tetraphenylborate and hexachloroplatinate , precipitate.

history

In 1871, Dmitri Iwanowitsch Mendeleev predicted the existence of an element that would occupy the then empty space in his periodic table. He described it as an alkali metal and named it eka- cesium .

In 1925 Dmitri Dobroserdow published a theoretical study in which he made predictions about the atomic weight as well as chemical and physical properties. He named the element russium .

A year later, in 1926, the English chemists Gerald Druce and Frederic H. Loring observed the spectral lines of the element when studying manganese sulfate . In 1929, the American physicist Fred Allison reported the discovery of the element while studying minerals and named the element Virginium after his home state Virginia. In 1936 the Romanian Horia Hulubei and the French Yvette Cauchois assumed that they had discovered the element and named it Moldavium . However, none of these discoveries has been confirmed by other scientists.

It was not until 1939 that Marguerite Perey was able to unequivocally prove the element as an isotope 223 Fr as a decay product of Actinium 227 Ac. It was initially called Actinium-K and renamed Francium (from French France "France", the discoverer's fatherland) in 1946 . The name was accepted by the International Association of Chemists in 1949 .

Physical Properties

The physical properties are essentially estimates determined by extrapolating the properties of the alkali metals or by model calculations. Investigations on compact samples of the metal or its compounds are due to the small amounts that can be produced (few attograms , ~ 10,000 atoms) and the high radioactivity (activity is about 2 million times higher than that of the same amount of 238 Pu : visible amounts would evaporate immediately) hardly possible.

safety instructions

Classifications according to the CLP regulation are not available because they only include chemical hazard and play a completely subordinate role compared to the hazards based on radioactivity . The latter also only applies if the amount of substance involved is relevant.

literature

  • Jean-Pierre Adloff, George B. Kauffman: Francium (Atomic Number 87), the Last Discovered Natural Element , The Chemical Educator, 10 (5), 2005, pp. 387-394, doi: 10.1333 / s00897050956a .
  • Eric Scerri : A tale of seven elements , Oxford University Press, Oxford, 2013

Web links

Wiktionary: Francium  - explanations of meanings, origins of words, synonyms, translations
Commons : Francium  - collection of images, videos and audio files

Individual evidence

  1. a b Harry H. Binder: Lexicon of chemical elements , S. Hirzel Verlag, Stuttgart 1999, ISBN 3-7776-0736-3 .
  2. The values ​​for the properties (info box) are taken from www.webelements.com (Francium) , unless otherwise stated .
  3. Manjeera Mantina, Adam C. Chamberlin, Rosendo Valero, Christopher J. Cramer, Donald G. Truhlar: Consistent van der Waals Radii for the Whole Main Group. In: J. Phys. Chem. A. 2009, 113, pp. 5806-5812, doi: 10.1021 / jp8111556 .
  4. a b c d e entry on francium in Kramida, A., Ralchenko, Yu., Reader, J. and NIST ASD Team (2019): NIST Atomic Spectra Database (ver. 5.7.1) . Ed .: NIST , Gaithersburg, MD. doi : 10.18434 / T4W30F ( https://physics.nist.gov/asd ). Retrieved June 13, 2020.
  5. a b c d e Entry on francium at WebElements, https://www.webelements.com , accessed on June 13, 2020.
  6. VV Oshchapovskii: A new method of calculation of the melting temperatures of crystals of Group 1A metal halides and francium metal. In: Russian Journal of Inorganic Chemistry. 59, 2014, pp. 561-567, doi : 10.1134 / S0036023614060163 .
  7. The hazards emanating from radioactivity do not belong to the properties to be classified according to the GHS labeling. With regard to other hazards, this element has either not yet been classified or a reliable and citable source has not yet been found.
  8. ^ A b William M. Haynes: CRC Handbook of Chemistry and Physics, 96th Edition . CRC Press, 2015, ISBN 978-1-4822-6097-7 , pp. 14 ( limited preview in Google Book search).
  9. ^ Earl K. Hyde: The Radiochemistry of Francium . National Academies, 1960, pp. 3 ( limited preview in Google Book Search).
  10. ^ A b c d e John Emsley: Nature's Building Blocks An AZ Guide to the Elements . OUP Oxford, 2011, ISBN 978-0-19-960563-7 , pp. 186 ( limited preview in Google Book search).
  11. ^ RK Sharma: Chemistry of Chemical Bonding . Discovery Publishing House, 2007, ISBN 978-81-8356-224-9 , pp. 310 ( limited preview in Google Book search).