RG

Roentgenium (symbol Rg) is a synthetic chemical element with atomic number 111. It is a highly radioactive metal that has not been observed in bulk and exists only in minute, short-lived quantities produced in particle accelerators.

Roentgenium was first synthesized in 1994 by a research team at the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt, Germany, using fusion-evaporation reactions between a bismuth-209 target and nickel-64 ions. The element was officially named roentgenium by IUPAC in 2004 in honor of Wilhelm Röntgen, the discoverer of X-rays.

It is placed in group 11 of the periodic table, in the d-block, and is expected to be a heavy, metallic element with properties analogous to the coinage metals, though the extreme instability of its isotopes prevents detailed observation. Roentgenium is produced only in minute quantities and decays rapidly by alpha decay or other modes.

Several isotopes have been synthesized, with half-lives ranging from milliseconds to minutes in known cases. Because of this short existence, chemical measurements are challenging and limited. Research has sought to explore whether roentgenium behaves like other group 11 elements in gas- and solution-phase experiments, but conclusions remain provisional due to the tiny numbers of atoms produced.

Due to its short half-life and production demands, roentgenium has no practical applications and is studied mainly to expand understanding of superheavy elements and the limits of the periodic table.