Untriseptium

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Untriseptium (pronEng|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 "Feynmanium" (symbol "Fy") is also informally used, because of Feynman's presentation of the speed of light problem described below.

The name "untriseptium" is a temporary IUPAC systematic element name.

History

Significance

The Bohr model exhibits difficulty for atoms with atomic number greater than 137, for the speed of an electron in a 1s electron orbital, v, is given by:

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

where Z is the atomic number, and α is the fine structure constant, a measure of the strength of electromagnetic interactions. [See for example R. Eisberg and R. Resnick, "Quantum Physics of Atoms, Molecules, Solids, Nuclei and Particles", Wiley (New York: 1985).] 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. Hence the non-relativistic Bohr model is clearly inaccurate when applied to such an element.

The relativistic Dirac equation also has problems for Z>137, for the ground state energy is

:$E=m\; c^2\; sqrt\{1-Z^2\; alpha^2\}$

where m is the rest mass of the electron. For Z>137, the wave function of the Dirac ground state is oscillatory, rather than bound, and there is no gap between the positive and negative energy spectra, as in the Klein paradox. [James D. Bjorken and Sidney D. Drell, "Relativistic Quantum Mechanics", McGraw-Hill (New York:1964).]

More accurate calculations including the effects of the finite size of the nucleus indicate that the binding energy first exceeds 2 m c² for Z>Z_cr$approx$173. For Z>Z_cr, if the innermost orbital is not filled, the electric field of the nucleus will pull an electron out of the vacuum, resulting in the spontaneous emission of a positron. [Walter Greiner and Stefan Schramm, "Am. J. Phys." 76, 509 (2008), and references therein.]

ee also

* Dubnium
* Eka-Rutherfordium — Eka-Dubnium — Eka-Seaborgium
* Untrihexium – Untrioctium
* Atomic orbital, section Element 137

References

External links

* [http://www.apsidium.com/elements/137.htm Likely properties of Untriseptium]
* [http://www.apsidium.com/ext_pt/expertab.htm Extended Periodic Table]