The Naming of Atoms

This is how it ought to be according to the official rules:

The official convention for naming atoms is that an "X-onium" atom is composed of a particle and its antiparticle, X+X-, whereas an electronic atom formed with an X+ as its nucleus is called "X-ium". Examples are "protonium" (p+p-) vs. "protium" (p+e-) and "positronium" (e+e-), the last of which cleverly qualifies under both conventions.

But this isn't the way it is! The µ+e- atom (chemical symbol Mu) is not called "muium" but instead is called "muonium", which properly ought to refer to µ+µ-. Why? The excuses are as follows:

Similar violations of convention apply for "pionium" (Can you say "piium"?) "kaonium" (How about "kaium"?) and other electronic atoms with exotic nuclei.

Still another term, "exotic atom", is generally reserved for atoms with normal nuclei in which an electron has been replaced by a heavier negative particle. The least exotic type is the muonic atom µ-Z, in which the negative muon often (for high atomic number Z) orbits so closely about the nucleus that other electrons and neighbouring atoms "see" the muonic atom as essentially a slightly enlarged and "fuzzy" nucleus of charge +Z-1 and atomic weight A+0.113 (the muon mass is 0.01126 of the proton's). But that's another story.

Author: JHB.     Figure created ~ 1985.    
Prepared by Jess H. Brewer
Last modified: Sat Nov 29 12:52:27 EST