Electrons, however, have a very small mass, much smaller than that of protons or neutrons. In fact, it's 1800 times smaller than a proton or a neutron. Now, if we look at this table and we look at their masses, a proton has one AMU, a neutron has one AMU. Now, AMU is simply atomic mass unit. We're going to discuss that in detail in another lecture. But an electron has a mass of 5.5 times ten to negative four AMU that's much smaller than that of proton or a neutron.