berkelium

 

(bûr'klēəm) [from Berkeley], artificially produced radioactive chemical element; symbol Bk; at. no. 97; mass no. of most stable isotope 247; m.p. about 1,050°C; b.p. about 2,590°C; sp. gr. 14 (estimated); valence +3, +4. Berkelium is believed to be similar to the other members of the actinide series and to terbium, its homolog in the lanthanide series. It is found in Group 3 of the periodic table. The 10 isotopes of berkelium that are known are all radioactive; the element has not been found in the earth's crust. Berkelium-247, the most stable isotope (half-life about 1,400 years), is difficult to produce; berkelium-249 (half-life 314 days) is more easily produced in weighable quantities and is used in studies of berkelium chemistry. Berkelium metal exists in two crystal modifications (see allotropy) and is chemically reactive; the chloride, fluoride, sulfide, nitrate, sulfate, perchlorate, oxide, and dioxide have been produced. Berkelium was the fifth transuranium element to be synthesized. It was discovered late in 1949 by Glenn T. Seaborg, Stanley G. Thompson, and Albert Ghiorso, who produced it by bombarding americium-241 with alpha particles in the cyclotron of the Univ. of California at Berkeley. Weighable quantities of the pure element were first isolated by Thompson and B. B. Cunningham in 1958.

Bk redirects here. For other uses of the abbreviation, see BK.

97 curium ← berkelium → californium Tb ↑ Bk ↓ (Uqs) Periodic Table - Extended Periodic Table
General
Name, Symbol, Number	berkelium, Bk, 97
Chemical series	Actinide
Group, Period, Block	n/a, 7, f
Appearance	unknown, probably silvery white or metallic gray
Standard atomic weight	(247)  g·mol−1
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·cm−3
Density (near r.t.)	(beta) 13.25  g·cm−3
Melting point	(beta) 1259 K (986 °C, 1807 °F)
Atomic properties
Oxidation states	3, 4
Electronegativity	1.3 (scale Pauling)
Ionization energies	1st: 601 kJ/mol
Miscellaneous
Crystal structure	hexagonal close-packed
Magnetic ordering	no data
Thermal conductivity	(300 K) 10  W·m−1·K−1
CAS registry number	7440-40-6
Selected 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
References

Berkelium (IPA: /bəˈkiːliəm/) is a synthetic element in the periodic table that has the symbol Bk and atomic number 97. A radioactive metallic element in the actinide series, berkelium 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 to be synthesized.

Notable characteristics

Weighable amounts of ²⁴⁹Bk (half-life 314 days) make 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 oxidize in air at elevated temperatures and would be soluble in dilute mineral acids.

X-ray diffraction techniques have been used to identify various berkelium compounds such as berkelium dioxide (BkO₂), berkelium fluoride (BkF₃), berkelium oxychloride (BkOCl), and berkelium trioxide (BkO₃). 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.

Like other actinides, berkelium bio-accumulates in skeletal tissue.^{[citation needed]} This element has no known uses outside of basic research and plays no biological role.

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.

Isotopes

19 radioisotopes of berkelium have been characterized, with the most stable being ²⁴⁷Bk with a half-life of 1380 years, ²⁴⁸Bk with a half-life of >9 years, and ²⁴⁹Bk with a half-life of 330 days. All of 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 (t_½ 23.7 hours). The isotopes of berkelium range in atomic weight from 235.057 u (²³⁵Bk) to 254.091 u (²⁵⁴Bk).

References

• Los Alamos National Laboratory - Berkelium
• It's Elemental - Berkelium

External links

• WebElements.com - Berkelium

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