Untriennium
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Untriennium (Template:PronEng, also called eka-actinium or dvi-lanthanum) is a hypothetical unsynthesized chemical element with atomic number 139 and symbol Ute.
The name untriennium is a temporary IUPAC systematic element name.
History
The name untriennium is an IUPAC systematic element name, the temporary name and symbol assigned to newly-synthesized and not-yet-synthesized chemical elements. A transuranic element receives a permanent name and symbol only after its synthesis has been confirmed. Transuranic elements beyond californium are always artificially produced, and usually end up being named for a scientist or the location of a laboratory that does work in atomic physics.
Significance
It is the first element that would have a filled type G electron shell, holding 18 electrons, and an electron in the overlaying type F orbital, in its ground state. However, due to drip instabilities, it is not known if this element is physically possible.