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In chemistry, transactinide elements are the chemical elements with atomic numbers greater than those of the actinides, the heaviest of which is lawrencium (103)^[1]. The transactinide elements are also called super-heavy elements.

All transactinide elements are also transuranium elements, that is, have an atomic number greater than that of uranium (92), an actinide. The further distinction of having a greater atomic number than the actinides is significant in several ways:

• The transactinide elements all have electrons in the 6d subshell in their ground state (and thus are placed in the d-block). The last actinide, lawrencium, also has one electron in the 6d subshell.
• Except for dubnium, even the longest-lasting isotopes of transactinide elements have extremely short half-lives, measured in seconds, or smaller units.
• The element naming controversy involved the first five or six transactinide elements. These elements thus used three-letter systematic names for many years after their discovery had been confirmed. (Usually the three-letter names are replaced with two-letter names relatively shortly after a discovery has been confirmed.)

All of the transactinide elements are radioactive and have only been obtained synthetically in laboratories. None of these elements has ever been collected in a macroscopic sample. Transactinide elements are all named after either nuclear physicists or important locations involved in the synthesis of the elements.

Nobelist Glenn T. Seaborg who first proposed the actinide concept which led to the acceptance of the actinide series also proposed the existence of a transactinide series ranging from element 104 to 121 and a superactinide series approximately spanning elements 122 to 153. One of the transactinide elements, Seaborgium, was named in his honor.

The term transactinide is an adjective, and is not commonly used alone as a noun to refer to the transactinide elements.

• 104 Rutherfordium, Rf
• 105 Dubnium, Db
• 106 Seaborgium, Sg
• 107 Bohrium, Bh
• 108 Hassium, Hs
• 109 Meitnerium, Mt
• 110 Darmstadtium, Ds
• 111 Roentgenium, Rg
• 112 Ununbium, Uub*
• 113 Ununtrium, Uut*
• 114 Ununquadium, Uuq*
• 115 Ununpentium, Uup*
• 116 Ununhexium, Uuh*
• 118 Ununoctium, Uuo*

* The synthesis of these elements has not been officially attested by IUPAC, while in several cases previous syntheses have been confirmed by other institutions or other methods. The names and symbols given are provisional as no names for the elements have been agreed on.

• Transuranium element
• Bose-Einstein condensate (also known as Superatom)
• Island of stability

1. ^ IUPAC Provisional Recommendations for the Nomenclature of Inorganic Chemistry (2004) (online draft of an updated version of the "Red Book" IR 3-6)