Unununium

Unununium (symbol Uuu) is the temporary systematic name that was used for the chemical element with atomic number 111 before it received its official name. It is a synthetic, highly unstable transactinide expected to occupy group 11 of the periodic table and to share some characteristics with the coinage metals copper, silver, and gold.

Unununium was first synthesized in 1994 by scientists at the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt, Germany, in a fusion-evaporation reaction using a 209Bi target and a 64Ni beam. The experiments produced a small number of atoms whose decay chains indicated a new element, later assigned to Z=111. The observed isotopes have extremely short half-lives, hampering detailed experimental study.

In 2004, IUPAC officially adopted the name roentgenium (Rg) for element 111, honoring Wilhelm Conrad Roentgen, the discoverer of X-rays. The former placeholder name unununium (Uuu) is now historical.

Because roentgenium remains a very short-lived synthetic element, it has no practical applications, and only a limited amount of chemical research has been possible. Theoretical predictions based on relativistic quantum chemistry suggest roentgenium would behave as a heavy member of group 11, with properties broadly akin to copper, silver, and gold but potentially altered by relativistic effects. The element continues to be of interest primarily for studies of the chemistry of superheavy elements and the limits of periodic trends.