The German team, led by Peter Armbruster at the Gesellschaft für schwerionenforschung (GSI) facility at Darmstadt, Germany, created Unununium by smashing nickel atoms into bismuth. The resulting atoms lasted for only four-thousandths of a second before decaying. The Unununium isotope created had an atomic mass of 272 and was made up of 111 protons and 161 neutrons in its nucleus. It is classified as a transition metal on the periodic table.

Even though Unununium is a fantastic name, in 2004 it was renamed Roentgenium (Rg) to honor the German physicist Wilhelm Conrad Röntgen, who discovered X-rays.