Why is the number of electrons not included in the atomic mass?

1 Answer
Dec 9, 2015

Because the mass contributed by electrons is dwarfed by the nuclear contribution.


Mass of an electron, #9.10xx10^(-31)*kg#.

Mass of a proton, #1.67xx10^(-27)*kg#.

There exists three orders of magnitude difference. Electronic mass can be ignored to a first approximation.