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# Untriseptium

 137 Uth ← untriseptium → Uto ↑Uts↓Uos
General
Name, Symbol, Number untriseptium, Uts, 137
Chemical series Superactinides
Group, Period, Block g17, 8, g
Appearance unknown
Standard atomic weight [364] u (supposition)  g·mol−1
Electron configuration [Uuo] 5g18 8s1
Electrons per shell 2, 8, 18, 32, 50, 18, 8, 1
Physical properties
Phase presumably solid
Miscellaneous
Selected isotopes
Main article: Isotopes of untriseptium
iso NA half-life DM DE (MeV) DP
References

Untriseptium (pronounced /ˌʌntraɪˈsɛptiəm/) is a chemical element which has not yet been observed to occur naturally or be synthesised. Its atomic number is 137 and symbol is Uts.

The name untriseptium is a temporary IUPAC systematic element name.

## History

The name untriseptium is used as a placeholder, as in scientific articles about the search for element 137. Transuranic elements (those beyond uranium) are, except for microscopic quantities and except for plutonium, always artificially produced, and usually end up being named for a scientist or the location of a laboratory that does work in atomic physics (see systematic element name for more information).

Because the significance of element 137 was first pointed out by the physicist Richard Feynman, element 137 is sometimes informally called Feynmanium (symbol Fy).

## Significance

In a non-relativistic approximation, the speed of an electron in a 1s electron orbital, v, can be obtained using the expression:

$v = Z \alpha c \approx \frac{Z c}{137.036}$

where Z is the atomic number, and α is the fine structure constant, a measure of the strength of electromagnetic interactions. Under this approximation, any element with an atomic number of greater than 137 would require 1s electrons to be traveling faster than c, the speed of light.

A complete analysis involving relativity reduces the speed of electrons, therefore allowing stable 1s orbits in the element 138 (Uto).