Scientists have been speculating on an even lighter element than Hydrogen .  Will this revolutionize chemistry? How can this be?  Hydrogen has just one proton and one electron. Well, Muonium also has an electron.... BUT NO PROTON .  There is an antimuon inside, which is lighter than a proton. The reason why you don't see Muonium in the Table of Elements is that it is not an element, for it is energetically impossible for this antimuon to transform into a proton. Thus the answer to the title above is NO. Might also mention Positronium, to be defined next. Some background. Back to hydrogen, its simplest isotope deuterium has one electron, one proton and one neutron, while tritium has one electron, one proton and two neutrons.   Sorry to keep bringing up these terms, but hydrogen is also known as protium There are 90 naturally-occurring elements on Earth, plus 18 or so other artificial ones. Muonium is artificial. Has one electron.  No proton or neutron. The nucleus is an antimuon, wh