Atomic and nuclear properties of materials:
Positronium (atom with e+ as nucleus)
* Ground state binding energy = Ry/2.
| Atomic number
+/- 1.097 526 752 |
+/- 0.000 000 005
+/- 1.021 991 03 |
+/- 0.000 000 09
| Mean lifetime|
Singlet: 125 ||
Doublet: 140 || ns
Is it reasonable to consider Ps as a chemical element?
It is bound electronically. If we consider atoms as having orbital
then the positron plays the role of nucleus.
It has a rich chemistry, as Google searches on "positronium halides,"
"positronium compounds," and other strings show. There are international
conferences on positronium chemistry.
In other exotic atoms such as muonium, pionium, and kaonium, the bound
muon or meson plays the role of an orbital electron instead of being the
nucleus. Although e-pi+ and other such atoms might equally well
regarded as elements, as would atoms with hypernuclei, these
unstable particles. An isolated positron is presumably as stable
One serious objection is that the positronium "nucleus" has non-zero
(e-pi+ and atoms with hypernuclei have nuclei with lepton number
zero, as do "normal" nuclei.)
- We are physicists, not chemists.