unununium , artificially produced radioactive chemical element; symbol Uuu; at. no. 111; mass number of most stable isotope 272; m.p., b.p., sp. gr., and valence unknown. Situated in group Ib of the periodic table, it is expected to have properties similar to those of gold.

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-life of 1.5 msec. No name has yet been suggested for element 111, which is therefore called unununium, from the Latin root un for one, under a convention for neutral temporary names proposed by the International Union of Pure and Applied Chemistry (IUPAC) in 1980.

See also synthetic elements; transactinide elements; transuranium elements.

The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2005, Columbia University Press. All rights reserved.

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