Mendelevium
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Mendelevium (symbol: Md) is a synthetic chemical element and a member of the actinoid series. It cannot be formed by neutron bombardment in a nuclear reactor, but must instead be produced in particle accelerators. Mendelevium cannot be produced in macroscopic quantities.
It was first prepared in 1955, and named after Dmitri Mendeleev in recognition of his development of the periodic table. Its chemistry is typical of the late actinoids, with both the +3 and +2 oxidation states stable in aqueous solution.
Contents
[hide]Preparation
Mendelevium was first prepared at the University of California Radiation Laboratory in Berkeley, California, in 1955 by the bombardment of 25399Es targets (roughly 109 atoms) with 41 MeV α-particles: just two atoms of the new element, later confirmed to be the A = 256 isotope, were produced per three-hour bombardment session, and only seventeen atoms in total were detected.[6]
- 25399Es(α,n)256101Md
The new element was identified by its elution time in ion-exchange chromatography: a spontaneous fission activity was observed both in the fermium fraction and in a fraction that eluted before the fermium, and this was taken to be a fermium daughter isotope produced by electron-capture decay of an isotope of element 101.[6] A larger-scale preparation in 1958 demostrated a parent–daughter relationship between 255101 and the previously-described 255Fm.[7]
The preparation of mendelevium still follows the same principles, although production rates of about a million atoms per hour can now be obtained.[8] The mendelevium atoms are collected on a thin metal film placed behind the einsteinium target (either 253Es or the longer-lived 254Es), or are carried in a stream of inert gas to a separate collection area. The collector foil is then dissolved in acid and the mendelevium is coprecipitated with lanthanum fluoride. The mendelevium is then separated from the lanthanum carrier and any lanthanoid fission products by ion-exchange chromatography using 10% aqueous ethanol saturated with hydrogen chloride as the eluant.[9] Final purification is acheived again by ion-exchange chromatography, this time using aqueous ammonium α-hydroxyisobutyrate as the eluant.[10]
Isotopes
There are 18 isotopes of mendelevium listed in NUBASE 2003,[11] with A = 245–262, of which 258Md is the longest lived with a half-life of 51.5(3) days. Nevertheless, most studies of mendelevium use 256Md (t½ = 77(2) min) as this is more readily produced by the 25399Es(α,n)256101Md or 25499Es(α,2n)256101Md reactions.[12]
Notes and references
Notes
- ↑ Jump up to: 1.0 1.1 1.2 1.3 The properties of mendelevium are only known through estimation and/or extrapolation.
References
- Jump up ↑ Pauling, Linus The Nature of the Chemical Bond, 3rd ed.; Ithaca, NY, 1960; pp 88–95. ISBN 0-8014-0333-2.
- Jump up ↑ Sugar, Jack Revised ionization energies of neutral actinides. J. Chem. Phys. 1974, 60 (10), 4103. DOI: 10.1063/1.1680874.
- Jump up ↑ 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.
- Jump up ↑ 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.
- Jump up ↑ Haire, R. G.; Gibson, J. K. Selected systematic properties and some recent investigations of actinide metals and alloys. J. Radioanal. Nucl. Chem. 1990, 143 (1), 35–51. DOI: 10.1007/BF02117545.
- ↑ Jump up to: 6.0 6.1 Ghiorso, A.; Harvey, B. G.; Choppin, G. R.; Thompson, S. G.; Seaborg, G. T. New Element Mendelevium, Atomic Number 101. Phys. Rev. 1955, 98 (5), 1518–19. DOI: 10.1103/PhysRev.98.1518.
- Jump up ↑ Phillips, L.; Gatti, R.; Chesne, A.; Muga, L.; Thompson, S. Discovery of a new Mendelevium Isotope. Phys. Rev. Lett. 1958, 1 (6), 215–21. DOI: 10.1103/PhysRevLett.1.215.
- Jump up ↑ Hulet, E. K.; Lougheed, R. W.; Brady, J. D.; Stone, R. E.; Coops, M. S. Mendelevium: Divalency and Other Chemical Properties. Science 1967, 158, 486–88. DOI: 10.1126/science.158.3800.486.
- Jump up ↑ Thompson, S. G.; Harvey, B. G.; Choppin, G. R.; Seaborg, G. T. Chemical Properties of Elements 99 and 100. J. Am. Chem. Soc. 1954, 76 (24), 6229–36. DOI: 10.1021/ja01653a004.
- Jump up ↑ Choppin, G. R.; Harvey, B. G.; Thompson, S. G. A new eluant for the separation of the actinide elements. J. Inorg. Nucl. Chem. 1956, 2 (1), 66–68. DOI: 10.1016/0022-1902(56)80105-X.
- Jump up ↑ Audi, G.; Bersillon, O.; Blachot, J.; Wapstra, A. H. The NUBASE evaluation of nuclear and decay properties. Nucl. Phys. A 2003, 729, 3–128. doi:10.1016/j.nuclphysa.2003.11.001, <http://amdc.in2p3.fr/nubase/Nubase2003.pdf>.
- Jump up ↑ 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, the Netherlands, 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>.
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., 1980; Chapter 12, pp 239–63. ACS Symposium Series, Vol. 131. ISBN 9780841205680. DOI: 10.1021/bk-1980-0131.ch012.
- Seaborg, Glenn T. The transcalifornium elements. J. Chem. Educ. 1959, 36 (1), 38–44. DOI: 10.1021/ed036p38.
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