transactinide

Transactinide is a term used in chemistry and nuclear science to describe the chemical elements with atomic numbers greater than 103, i.e., beyond the actinide series. These elements, sometimes called superheavy transactinides, are synthetic and have no stable isotopes. The known transactinides occupy the seventh period of the periodic table and include elements with atomic numbers 104 through 118.

All transactinides are produced artificially in particle accelerators by fusing lighter nuclei and are highly unstable, decaying within milliseconds to minutes. Most of their isotopes have short half-lives, making detailed study challenging. Production yields are extremely low, and experiments require sophisticated facilities and detection methods. The elements are highly reactive and exhibit relativistic effects that influence their chemical properties, often causing deviations from the trends observed in lighter homologues.

Examples and notable aspects include Rutherfordium (104), Dubnium (105), Seaborgium (106), Bohrium (107), Hassium (108), Meitnerium (109), Darmstadtium (110), Roentgenium (111), Copernicium (112), Nihonium (113), Flerovium (114), Moscovium (115), Livermorium (116), Tennessine (117), and Oganesson (118). Some transactinides have had limited chemical experiments; for instance, studies of nihonium and copernicium have advanced understanding of their behavior in solution or in compounds. Oganesson is predicted to be volatile and to show properties near the noble-gas end of the group, but experimental confirmation remains challenging due to extreme instability.

Significance and outlook: Research into transactinides tests theories of nuclear stability and relativistic quantum chemistry, informing models of the limits of the periodic table. Although practical applications are currently limited, the work enhances understanding of superheavy elements and guides future experiments aimed at discovering longer-lived nuclei.