berkelium

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berkelium

(bûr`klēəm) [from BerkeleyBerkeley
, city (1990 pop. 102,724), Alameda co., W Calif., on the E shore of San Francisco Bay just N of Oakland; inc. 1878. Originally (1820) part of a Spanish rancho, the site was purchased by Americans in 1853.
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], 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 seriesactinide series,
a series of radioactive metallic elements in Group 3 of the periodic table. Members of the series are often called actinides, although actinium (at. no. 89) is not always considered a member of the series.
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 and to terbiumterbium
[from Ytterby, a village in Sweden], metallic chemical element; symbol Tb; at. no. 65; at. wt. 158.92535; m.p. 1,356°C;; b.p. 3,123°C;; sp. gr. about 8.25; valence +3 or +4. Terbium is a soft, malleable, ductile, silver-gray metal.
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, its homolog in the lanthanide serieslanthanide series,
a series of metallic elements, included in the rare-earth metals, in Group 3 of the periodic table. Members of the series are often called lanthanides, although lanthanum (atomic number 57) is not always considered a member of the series.
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. It is found in Group 3 of the periodic tableperiodic table,
chart of the elements arranged according to the periodic law discovered by Dmitri I. Mendeleev and revised by Henry G. J. Moseley. In the periodic table the elements are arranged in columns and rows according to increasing atomic number (see the table entitled
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. 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-lifehalf-life,
measure of the average lifetime of a radioactive substance (see radioactivity) or an unstable subatomic particle. One half-life is the time required for one half of any given quantity of the substance to decay.
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 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 allotropyallotropy
[Gr.,=other form]. A chemical element is said to exhibit allotropy when it occurs in two or more forms in the same physical state; the forms are called allotropes.
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) and is chemically reactive; the chloride, fluoride, sulfide, nitrate, sulfate, perchlorate, oxide, and dioxide have been produced. Berkelium was the fifth transuranium elementtransuranium elements,
in chemistry, radioactive elements with atomic numbers greater than that of uranium (at. no. 92). All the transuranium elements of the actinide series were discovered as synthetic radioactive isotopes at the Univ.
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 to be synthesized. It was discovered late in 1949 by Glenn T. SeaborgSeaborg, Glenn Theodore
, 1912–99, American chemist, b. Ishpeming, Mich., grad. Univ. of California at Los Angeles, 1934, Ph.D. Univ. of California at Berkeley, 1937.
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, 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.

Berkelium

 

(Bk) an artificially obtained radioactive chemical element that belongs to the actinide group; its atomic number is 97. It has no stable isotopes. It was synthesized in December 1949 by the American scientists S. Thompson, A. Ghiorso, and G. Seaborg as a result of the irradiation of americium oxide 241Am203 by alpha particles in a cyclotron. It is named in honor of the city of Berkeley (California, USA), where a great deal of work in the synthesis and study of the actinides, including berkelium, was carried out. In choosing a name for berkelium, scientists noted that terbium, the homologue of berkelium in the lanthanide series (which occupies the same [eighth] place after lanthanum as does berkelium after actinium), was named in honor of the Swedish city Ytterby, in the environs of which many rare-earth minerals were first found. Isotopes of berkelium with mass numbers 243–250 and the nuclear isomer 248mBk are known. The longest-lived isotopes of berkelium are 247Bk (half-life T½ = 1,380 ± 250 yr), which emits alpha particles; and 249Bk (T½= 314 days), which emits beta particles (more than 99 percent) and alpha particles (2.2 x 10-3 percent). The latter is formed with low yield upon prolonged (several years’) irradiation by neutrons in a plutonium or uranium atomic reactor. In 1958, from irradiated plutonium, the American scientists B. Cunningham and S. Thompson first isolated berkelium in a quantity that could be weighed (approximately 0.4 micrograms).

The chemical identification of berkelium is carried out on the basis of the data of ion-exchange elution of its compounds. (For a detailed description of the method of identification, see ACTINIDESin vol. 1.) The properties of berkelium have been studied very little. Berkelium dioxide, 249BkO2, has been obtained in macroquantities. Research carried out with indicator quantities of berkelium has demonstrated that its most characteristic valence in aqueous solutions is +3. Like terbium, trivalent berkelium can be converted to the +4 oxidation state by strong oxidizing agents.

S. S. BERDONOSOV

berkelium

[′bər·klē·əm]
(chemistry)
A radioactive element, symbol Bk, atomic number 97, the eighth member of the actinide series; properties resemble those of the rare-earth cerium.

berkelium

a metallic transuranic element produced by bombardment of americium. Symbol: Bk; atomic no.: 97; half-life of most stable isotope, 247Bk: 1400 years; valency: 3 or 4; relative density: 14 (est.)