Fermium
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Fermium (symbol: Fm) is a synthetic chemical element and a member of the actinoid series. It is the heaviest element than can be formed by neutron bombardment of lighter elements, and hence the last element that can be prepared in macroscopic quantities.
Contents
Discovery
Fermium was first discovered in the fallout from the 'Ivy Mike' nuclear test (1 November 1952), the first successful test of a hydrogen bomb. Initial examination of the debris from the explosion had shown the production of a new isotope of plutonium, 24494Pu: this could only have formed by the absorption of six neutrons by a uranium-238 nucleus followed by two β− decays. At the time, the absorption of neutrons by a heavy nucleus was thought to be a rare process, but the identification of 24494Pu raised the possibility that still more neutrons could have been absorbed by the uranium nuclei, leading to new elements.[4] Element 99 (einsteinium) was quickly discovered on filter papers which had been flown through the cloud from the explosion (the same sampling technique that had been used to discover 24494Pu), specifically the isotope 25499Es resulting from the capture of 16 neutrons by uranium-238 followed by seven β− decays.[4] The discovery of fermium (Z = 100) required more material, as the yield was expected to be at least an order of magnitude lower than that of element 99, and so contaminated coral from the Enewetak atoll (where the test had taken place) was shipped to the University of California Radiation Laboratory in Berkeley, California, for processing and analysis. About two months after the test, a new component was isolated emitting high-energy α-particles (7.1 MeV) with a half-life of about a day. With such a short half-life, it could only arise from the β− decay of an isotope of einsteinium, and so had to be an isotope of the new element 100: it was quickly identified as 255100Fm (t½ = 20.07 hours).[4]
The discovery of the new elements, and the new data on neutron capture, was initially kept secret on the orders of the U.S. military.[4] Nevertheless, the Berkeley team were able to prepare elements 99 and 100 by civilian means, through the neutron bombardment of plutonium-239, and published this work in 1954 with the disclaimer that it was not the first studies that had been carried out on the elements.[5][6] The 'Ivy Mike' studies were declassified and published in 1955.[7]
The Berkeley team had been worried that another group might discover lighter isotopes of element 100 through ion bombardment techniques before they could publish their classified research,[4] and this proved to be the case. A group at the Nobel Institute for Physics in Stockholm independently discovered the element, producing an isotope later confirmed to be 250100Fm by bombarding a 23892U target with oxygen-16 ions, and published their work in May 1954.[8] Nevertheless, the priority of the Berkeley team was generally recognized, and with it the prerogative to name the new element in honour of the recently deceased Enrico Fermi, the developer of the first artificial self-sustained nuclear reactor.
Notes and references
Notes
- ↑ 1.0 1.1 1.2 Many of the properties of fermium are only known through estimation and/or extrapolation. The melting point and metallic radius were estimated on the basis of the enthalpy change of atomization and comparison with divalent lanthanoids; the electronegativity was estimated on the basis of periodic trends; the ionic radius was estimated from the behaviour of Fm3+ α-hydroxyisobutyrate (α-HIB) complexes on ion exchange columns, and agrees well with theoretical calculations. The electron configuration and thermodynamic properties are directly determined.
References
- ↑ 1.0 1.1 1.2 Haire, Richard G.; Gibson, John K. The enthalpy of sublimation and thermodynamic functions of fermium. J. Chem. Phys. 1989, 91 (11), 7085–96. DOI: 10.1063/1.457326.
- ↑ David, F.; Samhoun, K.; Guillaumont, R.; Edelstein, N. Thermodynamic properties of 5f elements. J. Inorg. Nucl. Chem. 1978, 40 (1), 69–74. DOI: 10.1016/0022-1902(78)80309-1.
- ↑ Brüchle, W.; Schädel, M.; Scherer, U. W.; Kratz, J. V.; Gregorich, K. E.; Lee, D.; Nurmia, M.; Chasteler, R. M., et al. The hydration enthalpies of Md3+ and Lr3+. Inorg. Chim. Acta 1988, 146 (2), 267–76. DOI: 10.1016/S0020-1693(00)80619-2.
- ↑ 4.0 4.1 4.2 4.3 4.4 Ghiorso, Albert Einsteinium and Fermium. Chem. Eng. News 2003, 81 (36), <http://pubs.acs.org/cen/80th/einsteiniumfermium.html>.
- ↑ Thompson, S. G.; Ghiorso, A.; Harvey, B. G.; Choppin, G. R. Transcurium Isotopes Produced in the Neutron Irradiation of Plutonium. Phys. Rev. 1954, 93 (4), 908. DOI: 10.1103/PhysRev.93.908.
- ↑ Choppin, G. R.; Thompson, S. G.; Ghiorso, A.; Harvey, B. G. Nuclear Properties of Some Isotopes of Californium, Elements 99 and 100. Phys. Rev. 1954, 94 (4), 1080–81. DOI: 10.1103/PhysRev.94.1080.
- ↑ Ghiorso, A.; Thompson, S. G.; Higgins, G. H.; Seaborg, G. T.; Studier, M. H.; Fields, P. R.; Fried, S. M.; Diamond, H., et al. New Elements Einsteinium and Fermium, Atomic Numbers 99 and 100. Phys. Rev. 1955, 99 (3), 1048–49. DOI: 10.1103/PhysRev.99.1048.
- ↑ Atterling, Hugo; Forsling, Wilhelm; Holm, Lennart W.; Melander, Lars; Åström, Björn Element 100 Produced by Means of Cyclotron-Accelerated Oxygen Ions. Phys. Rev. 1954, 95 (2), 585–86. DOI: 10.1103/PhysRev.95.585.2.
Further reading
- Hulet, E. K. Chemistry of the Heaviest Actinides: Fermium, Mendelevium, Nobelium, and Lawrencium. In Lanthanide and Actinide Chemistry and Spectroscopy; Edelstein, Norman M., Ed.; American Chemical Society: Washington, D.C.; Chapter 12, pp 239–63. ACS Symposium Series, Vol. 131. ISBN 9780841205680. DOI: 10.1021/bk-1980-0131.ch012.
- Silva, Robert J. Fermium, Mendelevium, Nobelium, and Lawrencium. In The Chemistry of the Actinide and Transactinide Elements, 3rd ed.; Morss, Lester R.; Edelstein, Norman M.; Fuger, Jean, Eds.; Springer: Dordrecht, 2006; Vol. 3, Chapter 13, pp 1621–51. doi:10.1007/1-4020-3598-5_13, <http://radchem.nevada.edu/classes/rdch710/files/Fm%20to%20Lr.pdf>
External links
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