Berkelium

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97 curiumberkeliumcalifornium
Tb

Bk

(Uqs)
Bk-TableImage.png
General
Name, Symbol, Number berkelium, Bk, 97
Chemical series actinides
Group, Period, Block n/a, 7, f
Appearance unknown, probably silvery
white or metallic gray
Atomic mass (247) g/mol
Electron configuration [Rn] 5f9 7s2
Electrons per shell 2, 8, 18, 32, 27, 8, 2
Physical properties
Phase solid
Density (near r.t.) (alpha) 14.78 g/cm³
Density (near r.t.) (beta) 13.25 g/cm³
Melting point (beta) 1259 K
(986 °C, 1807 °F)
Atomic properties
Oxidation states 3, 4
Electronegativity 1.3 (Pauling scale)
Ionization energies 1st: 601 kJ/mol
Miscellaneous
Crystal structure hexagonal close-packed
Magnetic ordering no data
Thermal conductivity (300 K) 10 W/(m·K)
CAS registry number 7440-40-6
Notable isotopes
Main article: Isotopes of berkelium
iso NA half-life DM DE (MeV) DP
245Bk syn 4.94 d ε 0.810 245Cm
α 6.455 241Am
246Bk syn 1.8 d α 6.070 242Am
ε 1.350 246Cm
247Bk syn 1380 y α 5.889 243Am
248Bk syn >9 y α 5.803 244Am
249Bk syn 330 d α 5.526 245Am
SF - -
β- 0.125 249Cf

Berkelium (chemical symbol Bk, atomic number 97) is a synthetic, radioactive chemical element, classified as an actinide. It was first synthesized by bombarding americium with alpha particles (helium ions) and was named after Berkeley, California and the University of California, Berkeley. Berkelium was the fifth transuranic element[1] to be synthesized. Currently, the main interest in this element lies in basic research, and practical applications have yet to be developed.

Contents

History

Berkelium was first synthesized by Glenn T. Seaborg, Albert Ghiorso, Stanley G. Thompson, and Kenneth Street, Jr., at the University of California, Berkeley in December 1949. The team used a cyclotron to bombard a milligram-sized target of 241Am with alpha particles to produce 243Bk (half-life 4.5 hours) and two free neutrons. One of the longest lived isotopes of the element, 249Bk (half-life 330 days), was later synthesized by subjecting a 244Cm target with an intense beam of neutrons.

Notable characteristics

Berkelium is an inner transition metal of the actinide series, located in period 7 of the periodic table, between curium and californium. Weighable amounts of 249Bk (half-life 314 days) have been produced, making it possible to determine some of its properties using macroscopic quantities. As of 2004, it had not been isolated in its elemental form, but it is predicted to be a silvery metal that would easily undergo oxidation in the air at elevated temperatures and would be soluble in dilute mineral acids.

Isotopes

Many radioisotopes of berkelium have been characterized, with the most stable being 247Bk, with a half-life of 1,380 years; 248Bk, with a half-life of more than 9 years; and 249Bk, with a half-life of 330 days. All the remaining radioactive isotopes have half-lives that are less than 5 days, and the majority of these have half-lives that are less than 5 hours. This element also has 2 meta states, with the most stable being 248mBk (t½ 23.7 hours). The isotopes of berkelium range in atomic weight from 235.057 amu (235Bk) to 254.091 amu (254Bk).

Compounds

X-ray diffraction techniques have been used to identify various berkelium compounds such as berkelium dioxide (BkO2), berkelium trioxide (BkO3), berkelium fluoride (BkF3), and berkelium oxychloride (BkOCl). In 1962, visible amounts of berkelium chloride (BkCl3) were isolated that weighed 3 billionths of a gram. This was the first time visible amounts of a pure berkelium compound were produced.

Biological role

Berkelium plays no biological role. It is thought that, like other actinides, it is capable of bioaccumulation in skeletal tissue.

See also

Notes

  1. "Transuranic elements" are chemical elements with atomic numbers greater than that of uranium (atomic number 92).

References

  • Emsley, John. 2001. Nature's Building Blocks: An A–Z Guide to the Elements. Oxford University Press. ISBN 0198503407
  • Greenwood, N. N., and A. Earnshaw. 1998. Chemistry of the Elements, 2nd ed. Oxford, UK; Burlington, MA: Butterworth-Heinemann. ISBN 0750633654. Online version. Retrieved April 12, 2007.
  • Hampel, Clifford A. 1968. The Encyclopedia of the Chemical Elements. New York: Reinhold Book Corp. ISBN 0442155980
  • Morss, Lester R., Norman M. Edelstein, and Jean Fuger, eds. 2006. The Chemistry of the Actinide and Transactinide Elements, 3rd ed., 5 vols. Joseph J. Katz, adapter. Dordrecht: Springer. ISBN 1402035551
  • Stwertka, Albert. 1998. Guide to the Elements, rev. ed. Oxford University Press. ISBN 0-19-508083-1

External links

  • Berkelium – Los Alamos National Laboratory, Chemistry Division. Retrieved March 14, 2007.
  • Berkelium – WebElements. Retrieved March 14, 2007.
  • It's Elemental: Berkelium – Jefferson Lab. Retrieved March 14, 2007.

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