Berkelium

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curium ← berkelium → californium
Tb
↑
Bk
↓
–
Atomic properties
Atomic number 97
Electron configuration [Rn] 5f9 7s2
Physical properties[1][2][3]
Melting point 1272(22) K (999 °C)[Note 1]
Boiling point 2900(50) K (2625 °C)
Density 14.78 g cm−3
Chemical properties[4]
Electronegativity 1.3 (Pauling)[Note 2]
Ionization energy[5][6]
6.1979(2) eV
598.01(2) kJ mol−1
Atomic radii[3][7][8]
Metallic radius 170 pm
Ionic radius 96 pm (Bk3+, Oh)[Note 3]
83 pm (Bk4+, Oh)
Thermodynamic properties[2][9]
Standard entropy 76.2(13) J K−1 mol−1
Enthalpy change of atomization 310(6) kJ mol−1
Enthalpy change of fusion 7.92 kJ mol−1
Miscellaneous
CAS number 7440-40-6
Where appropriate, and unless otherwise stated, data are given for 100 kPa (1 bar) and 298.15 K (25 °C).
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Berkelium (symbol: Bk) is a synthetic chemical element and a member of the actinoid series. It is named after the city of Berkeley, California, the location of the University of California Radiation Laboratory where it was discovered in 1949.

Discovery

Berkelium was first produced in 1949 by the bombardment of an americium-241 target with α-particles: the nuclear reaction is 24195Am(α,2n)24397Bk. The product berkelium-243 (t½ = 4.5(2) hours) was separated by ion exchange chromatography, where it elutes just ahead of curium, its β+-decay product.[10][11][Note 4]

The new element was named after the city of Berkeley, California, by analogy with its lanthanoid homologue terbium, named after the village of Ytterby in Sweden.[11]

Production

The first macroscopic quantities (0.8 µg) of berkelium were isolated in 1958 after a six-year irradiation of plutonium-241 with neutrons.[12] This method, which produces the isotope 249Bk (t½ = 330(4) days), is still the only way of producing weighable amounts of the element.[13] The major source is the 85 MW High Flux Isotope Reactor (HFIR) at the Oak Ridge National Laboratory in Tennessee, USA, which is dedicated to the production of transcurium (Z > 96) elements.[14][Note 5] In a "typical processing campaign" at Oak Ridge, tens of grams of curium are irradiated to produce decigram quantities of californium, milligram quantities of berkelium and einsteinium and picogram quantities of fermium.[16]

Notes and references

Notes

  1. ↑ The melting point quoted here is the weighted mean of the values found by Fahey et al. (1972)[1] and Ward et al. (1982).[2]
  2. ↑ The Pauling electronegativity was estimated from periodic trends rather than being calculated from bond energy data.
  3. ↑ The quoted atomic radii are based on the usual convention that r(O2−, Oh) = 140 pm; on the alternative convention of r(F−, Oh) = 119 pm, the value would be 110 pm for octahedral Bk3+.
  4. ↑ The decay of 243Bk was initially thought to be by electron capture: the product nuclide is the same in both cases, 24396Cm (t½ = 29.1(1) years).
  5. ↑ The Research Institute of Atomic Reactors (NIIAR) in Dimitrovgrad, Russia, is also a producer of transcurium elements.[15] The SM-2 loop reactor at NIIAR has similar power and flux levels to the High Flux Isotope Reactor at Oak Ridge, and so production capacities for transcurium elements are expected to be similar at the two facilities, although the quantities produced at NIIAR are not published.

References

  1. ↑ 1.0 1.1 Fahey et al., 1972
  2. ↑ 2.0 2.1 2.2 Ward et al., 1982
  3. ↑ 3.0 3.1 Peterson et al., 1971
  4. ↑ Pauling, Linus The Nature of the Chemical Bond, 3rd ed.; Ithaca, NY, 1960. ISBN 0-8014-0333-2.
  5. ↑ Köhler, S.; Deißenberger, R.; Eberhardt, K.; Erdmann, N.; Herrmann, G.; Huber, G.; Kratz, J. V.; Nunnemann, M., et al. Determination of the first ionization potential of actinide elements by resonance ionization mass spectroscopy. Spectrochim. Acta, Part B 1997, 52 (6), 717–26. DOI: 10.1016/S0584-8547(96)01670-9.
  6. ↑ Erdmann, N.; Nunnemann, M.; Eberhardt, K.; Herrmann, G.; Huber, G.; Köhler, S.; Kratz, J. V.; Passler, G., et al. Determination of the first ionization potential of nine actinide elements by resonance ionization mass spectroscopy (RIMS). J. Alloys Compd. 1998, 271–273, 837–40. DOI: 10.1016/S0925-8388(98)00229-1.
  7. ↑ Shannon and Prewitt, 1969
  8. ↑ Shannon, R. D. Revised effective ionic radii and systematic studies of interatomic distances in halids and chalcogenides. Acta Crystallogr. A 1976, 32 (5), 751–67. DOI: 10.1107/S0567739476001551.
  9. ↑ Ward and Hill, 1976
  10. ↑ Thompson, S. G.; Ghiorso, A.; Seaborg, G. T. Element 97. Phys. Rev. 1950, 77 (6), 838–39. DOI: 10.1103/PhysRev.77.838.2.
  11. ↑ 11.0 11.1 Thompson, S. G.; Ghiorso, A.; Seaborg, G. T. The New Element Berkelium (Atomic Number 97). Phys. Rev. 5, 80, 781–89. DOI: 10.1103/PhysRev.80.781.
  12. ↑ Cunningham, 1959
  13. ↑ Hobart, David E.; Peterson, Joseph R. Berkelium. 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 10, pp 1444–98. doi:10.1007/1-4020-3598-5_10, <http://radchem.nevada.edu/classes/rdch710/files/berkelium.pdf>.
  14. ↑ High Flux Isotope Reactor; Oak Ridge National Laboratory, <http://neutrons.ornl.gov/facilities/HFIR/>. (accessed 23 September 2010).
  15. ↑ Радионуклидные источники и препараты; Research Institute of Atomic Reactors, <http://www.niiar.ru/?q=radioisotope_application>. (accessed 26 September 2010).
  16. ↑ Porter, C. E.; Riley, F. D., Jr.; Vandergrift, R. D.; Felker, L. K. Fermium Purification Using Teva™ Resin Extraction Chromatography. Sep. Sci. Technol. 1997, 32 (1–4), 83–92. DOI: 10.1080/01496399708003188.

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