Superactinide

Superactinides are the undiscovered chemical elements from number 121 (Unbiunium) until 153 (Unpenttrium), at which the 5g and 6f- electron shells are filled up. The superactinide series follows the transactinide series and sits below it on the extended periodic table of the elements. The theoretical existence of the series was proposed by Glenn T. Seaborg, winner of the 1951 Nobel Prize in Chemistry.