Atomic mass represents the weight of an atoms protonsneutronsand electrons however the atomic mass is generally used to refer to just the number of protons and neytrons why?

Answer 1

Each electron weighs only about 0.0005 Atomic Mass unit, but protons and neutrons weigh 1 atomic mass unit each. Since there are the same number of protons, and usually even more neutrons, in an atom as there are protons, the weight of the electrons can be neglected in most chemical calculations.