Untriennium





Untriennium (, also called eka-actinium or dvi-lanthanum) is an unsynthesized chemical element with atomic number 139 and symbol Ute.

The name untriennium is a temporary IUPAC systematic element name.

Significance
In a non-relativistic approximation, the speed of an electron in a 1s electron orbital, v, is estimated to approach the speed of light for 1s orbitals in element 138. At element 139, it is predicted that these electrons will have a speed in excess of c and as such would not have stable electron orbitals.

It is the first element with a filled type G electron shell, holding 18 electrons, and an electron in the overlaying type F orbital, in its ground state.