June 7, 2011 | 3
This year has been designated the International Year of Chemistry, so it is only fitting that two new members of the atomic family should be welcomed in during 2011.
The elements with atomic numbers of 114 and 116 have been recognized by the International Union of Pure and Applied Chemistry (IUPAC), which credited a Russia–U.S. collaboration with their discovery. An element’s atomic number describes the number of protons in its nucleus. IUPAC has invited the collaborating scientists, from the Joint Institute for Nuclear Research in Dubna, Russia, and Lawrence Livermore National Laboratory in California, to propose names for the new elements. For now elements 114 and 116 retain their provisional number-based names, ununquadium and ununhexium, respectively. Both the newly vetted elements have higher atomic numbers than any element yet recognized by IUPAC. All elements with atomic numbers above 92 (the atomic number of uranium) decay relatively quickly and are mostly man-made, although elements 93 and 94 (neptunium and plutonium) do exist naturally in trace quantities.
Claims for the synthesis of both fleeting man-made elements have been around for more than a decade. In 1999 the Dubna group reported having produced element 114 with other collaborators via fusion reactions between calcium and plutonium. And in 2000 the Dubna group and the Livermore group announced that they had synthesized element 116 by fusing calcium and curium. But IUPAC operates conservatively, waiting for evidence that shows the production of a new element "beyond reasonable doubt."
For elements 114 and 116, experiments by the Dubna–Livermore group in 2004, and subsequent confirmation work in the years that followed, finally met that standard. Evidence for proposed elements 113, 115 and 118 does not yet satisfy IUPAC’s criteria for discovery. History has justified that caution. A 1999 study claiming the production of element 118, a synthesis that was claimed to have also generated elements 114 and 116 as radioactive decay products, was later retracted by the study’s authors.
Elements 114 and 116 will join element 112, which IUPAC recognized in 2009, as newly official members of the periodic table. Element 112, whose discovery was credited to a German team, is now known as copernicium, or Cn, after Polish astronomer Nicolaus Copernicus. Its recognition paved the way for the acceptance of elements 114 and 116, which produce copernicium as part of their decay chains. In one decay chain, for instance, element 116 decays to element 114 with a lifetime of about 26 milliseconds. Then element 114 decays to copernicium after an average lifetime of 1.1 seconds.
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