b`nēəm), artificially produced radioactive chemical element; symbol Db; at. no. 105; mass number of most stable isotope 262; m.p., b.p., and sp. gr. unknown; valence +5. Situated in Group 5 of the periodic table periodic 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..... Click the link for more information. , it has properties similar to those of niobium niobium (nīō`bēəm), metallic chemical element; symbol Nb; at. no. 41; at. wt. 92.9064; m.p. about 2,468°C;; b.p.
..... Click the link for more information. and tantalum tantalum (tăn`tələm) [from Tantalus ], metallic chemical element; symbol Ta; at. no. 73; at. wt. 180.9479; m.p. 2,996°C;; b.
..... Click the link for more information. .
In 1968 a Soviet team led by G. N. Flerov at the Joint Institute for Nuclear Research at Dubna announced the discovery of element 105. They claimed that in 1967 they had isolated isotopes with mass numbers 260 and 261 and half-lives half-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.
..... Click the link for more information. of 0.1 sec and 3 sec, respectively, by bombarding americium-243 atoms with neon-22 ions. In 1970 the same team announced that by using the same americium and neon isotopes but a different detection technique they had created an isotope of element 105 with mass number 261 and a half-life of 2 sec; they suggested that element 105 be named nielsbohrium to honor the Danish physicist Niels Bohr Harald August Bohr, 1887–1951, a mathematician, taught (1915–30) at the College of Technology in Copenhagen and in 1930 became professor at the Univ. of Copenhagen. His most noted contribution to mathematics was his formulation of the theory of almost periodic functions.
..... Click the link for more information. . In 1970, an American research team led by A. Ghiorso at the Lawrence Berkeley National Laboratory announced that, while they had been unable to confirm the Dubna group's results, they had synthesized an isotope of element 105 by another route. They bombarded californium-249 atoms with nitrogen-15 ions to create an isotope with mass number 260 and a half-life of 1.6 sec. Disputing the Soviet claim of discovery, the Americans suggested the name hahnium to honor the German chemist and physicist Otto Hahn Hahn, Otto (ô`tō hän), 1879–1968, German chemist and physicist.
..... Click the link for more information. .
An international committee set up to resolve such disputes decided in 1992 that the Berkeley and Dubna laboratories should share credit for the discovery. The syntheses of at least nine isotopes of dubnium, with half-lives ranging from 1.2 sec (Db-259) to 34 sec (Db-262), have been confirmed. In 1994 a committee of the International Union of Pure and Applied Chemistry (IUPAC), convened to resolve naming disputes for the transactinide elements transactinide elements (trăns'ăk`tənīd'), in chemistry, elements with atomic numbers greater than that of lawrencium (at.
..... Click the link for more information. , recommended that element 105 be named joliotium, symbol Jl, after the French physicist Frédéric Joliot-Curie Frédéric Joliot-Curie (frādārēk`), 1900–1958, formerly Frédéric Joliot, and
..... Click the link for more information. . In 1997 the name dubnium was accepted internationally for element 105, in recognition of the pioneering work done at the Dubna laboratory.
See also synthetic elements synthetic elements, in chemistry, radioactive elements that were not discovered occurring in nature but as artificially produced isotopes. They are technetium (at. no. 43), which was the first element to be synthesized, promethium (at. no. 61), astatine (at. no.
..... Click the link for more information. ; transuranium elements transuranium 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.
..... Click the link for more information. .
dubnium
dubnium [′düb·nē·əm]
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