The Naming of Atoms

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

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:

• No one could pronounce "muium".
• The name became popular before the current conventions were formally established, and you can't change all the literature retroactively. (Otherwise electrons would be positively charged!)
• No one has ever observed µ⁺µ^- and there are few prospects for doing so in the near future, so there is no practical conflict.

Still another term, "exotic atom", is generally reserved for atoms with normal nuclei in which an electron has been replaced by a heavier negative particle.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.