|Name, Symbol, Number||berkelium, Bk, 97|
|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|
|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)
|Oxidation states||3, 4|
|Electronegativity||1.3 (Pauling scale)|
|Ionization energies||1st: 601 kJ/mol|
|Crystal structure||hexagonal close-packed|
|Magnetic ordering||no data|
|Thermal conductivity||(300 K) 10 W/(m·K)|
|CAS registry number||7440-40-6|
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 to be synthesized. Currently, the main interest in this element lies in basic research, and practical applications have yet to be developed.
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.
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.
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).
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.
Berkelium plays no biological role. It is thought that, like other actinides, it is capable of bioaccumulation in skeletal tissue.
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