ununseptium

(redirected from Eka-astatine)

ununseptium

(o͞on'o͞onesĕp`tēəm), artificially produced radioactive chemical elementelement,
in chemistry, a substance that cannot be decomposed into simpler substances by chemical means. A substance such as a compound can be decomposed into its constituent elements by means of a chemical reaction, but no further simplification can be achieved.
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; symbol Uus; at. no. 117; mass number of most stable isotopeisotope
, in chemistry and physics, one of two or more atoms having the same atomic number but differing in atomic weight and mass number. The concept of isotope was introduced by F.
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 294; m.p., b.p., sp. gr., and valence unknown. Ununseptium is a member of Group 17 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 halogenshalogen
[Gr.,=salt-bearing], any of the chemically active elements found in Group 17 of the periodic table; the name applies especially to fluorine (symbol F), chlorine (Cl), bromine (Br), and iodine (I).
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, and may have properties similar to astatineastatine
[Gr.,=unstable], semimetallic radioactive chemical element; symbol At; at. no. 85; at. wt. of most stable isotope 210; m.p. 302°C; (estimated); b.p. 337°C; (estimated); density unknown; valence believed to be +1, +3, +5, or +7.
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.

In 2010 scientists from the Joint Institute for Nuclear Research in Dubna, Russia, announced that they had bombarded (2009) berkelium-249 atoms with calcium-48 ions to create two forms of ununseptium. The Uus-294 isotope, with a half-life of 78 milliseconds, decayed through alpha-particle emission into dubnium (element 105), while the lighter Uus-293, with a half-life of 14 milliseconds, decayed down to roentgenium (element 111). The Russian researchers collaborated with American scientists at Vanderbilt Univ. and the Oak Ridge National Laboratory, which produced the berkelium used in the experiment. In 2015 the International Union of Pure and Applied Chemistry (IUPAC) confirmed the discovery. No name has yet been formally adopted for element 117, which is therefore called ununseptium, from the Latin roots un for one and sept for seven, under a convention for neutral temporary names proposed by IUPAC in 1980, but in 2016 the element's discoverers proposed "tennessine," to honor the home state of the American collaborators.

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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