This sounds like a silly question but if Z (atomic number) is defined as the number of protons in a nucleus. Why does Z=-1 for a beta minus particle? (since it is just an electron) I know what is happening with the decay that a up quark turns into a down quark so that a neutron turns into a proton, electron and electron neutrino but I see no reason other than saying the atomic number must be conserved in the decay equation for Z=-1 for the beta particle. It seems to me that we have decided that Z=-1 to fit a rule for conservation of atomic number and for no other reason. I know that there must be an error in my thinking somewhere but where?