roentgenium

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roentgenium,

artificially produced radioactive chemical element; symbol Rg; at. no. 111; mass number of most stable isotope 280; m.p., b.p., sp. gr., and valence unknown. Situated in Group 11 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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, it is expected to have properties similar to those of goldgold,
metallic chemical element; symbol Au [Lat. aurum=shining dawn]; at. no. 79; at. wt. 196.96657; m.p. 1,064.43°C;; b.p. 2,808°C;; sp. gr. 19.32 at 20°C;; valence +1 or +3.
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.

In 1994 an international research team led by Peter Armbruster and Sigurd Hofmann at the Institute for Heavy Ion Research at Darmstadt, Germany bombarded bismuth-209 atoms with nickel-64 ions. In an 18-day experiment, three atoms were unambiguously identified as an isotope of element 111 with mass number 272 and a 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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 of 1.5 msec. The discovery was officially confirmed in 2003, and the discoverers named the element in honor of Wilhelm Conrad RoentgenRoentgen or Röntgen, Wilhelm Conrad
, 1845–1923, German physicist. His notable research in many fields of physics, especially thermology, mechanics, and electricity, has been overshadowed by his discovery
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. The most stable isotope, roentgenium-280, has a half-life of approximately 3.6 sec.

See also synthetic elementssynthetic 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.
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; transactinide elementstransactinide elements
, in chemistry, elements with atomic numbers greater than that of lawrencium (at. no. 103), the last member of the actinide series. See transuranium elements.
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; transuranium elementstransuranium 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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