Hi, I'm taking introductory particle physics and this is related to the first couple of chapters in Griffiths. If I draw a Feynman diagram for a particular process, what conservation laws must hold at each vertex? Mainly looking at QED processs but as far as I can work out energy and momentum are the main ones. It also seems that one cannot go from one lepton family to another or one quark family to another at a vertex. Anything else I'm missing or incorrectly stating? Also, when we have virtual particles, are there any restrictions (apart from those above) on what I can use as a virtual particle? Somehow, its not too clear in Griffiths and I can't find a set of rules online either. Thank you!