In my biology textbook there is a short chapter on chemistry, in which it says the mass of 1 proton = the mass of 1 neutron = 1 amu. Hydrogen is made up of 1 proton and 1 electron and has an atomic weight of 1.0079 amu's. Logically, the mass of 1 electron should be .0079 amu's. However, on the same periodic table, it says that helium (2 neutrons, 2 protons, and 2 electrons) has an atomic mass of 4.0026, which means that the mass of 1 electron should be .0013 amu's. I am confused and could not find anything explaining this on google. Is there more subatomic particles than protons, electrons, and neutrons which weigh enough to matter, or is the idea that 1 proton = 1 neutron = 1 amu off? Please Register or Log in to view the hidden image!