Ok, I’m staying up with you so far (and removing a LOT of dust that settled on the high school chemistry information!), but I keep getting hung up on the atomic weight. Is the atomic weight based solely on the nucleus? Do the atoms have zero weight or is it too negligible to make any difference?
BTW, thanks for your patience in helping me understand this stuff. I really enjoy learning new things, no matter how many times I have learned it before!!
The neutron and proton masses are both close to 940 MeV/c^2. [Neutron is actually slightly heavier.] The electron is 0.512 MeV/c^2. So, it takes ~2000 electron masses to make a nucleon mass. Since the most massive element has only slightly more than 100 electrons, the electron mass is always negligible compared to nuclear mass (in chemistry.) The biggest variation in nuclear masses actually come from averaging isotope species and (to a much smaller extent) differences in binding energy.