The name untriseptium is used as a placeholder for the element 137 until it is discovered. Transuranic elements beyond plutonium 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.

See systematic element name.

Significance

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

$v = Z \alpha c = \frac{Z c}{137.0036}$

where Z is the atomic number, and α is the fine structure constant, a measure of the strength of electromagnetic interactions. Therefore any element with an atomic number of greater than 137 would require 1s electrons to be traveling faster than c, the speed and light, and as such would not have stable electron orbitals.

A more thorough analysis, involving general relativity slightly reduces the speed of electrons, therefore allowing stable orbits in the element 138 (Uth).

As the nature of the central charge does not feature in the derivation of the above result, if it were possible to have an alternate object as a central charge; for instance a small, charged black hole (allowed under contemporary physical laws); forming the core of an atom, it could not have a charge of greater than -137 times that of the electron.

External Links

Fenyman Online - Describes why element 137 is the last classicaly stable element.
Likely propeties of Untriseptium

Categories: Chemical elements | Nuclear physics