Question

When the mass of the boron atom is calculated, the mass of the electrons is ignored. Why is the mass of the electrons ignored?

Answer 1

Because electron mass is so insignificant compared to proton and neutron mass that it CAN be ignored.

Explanation:

The mass of a proton is approx. `1.673×10^(−27)* kg`; the mass of a neutron is slightly larger. On the other hand, the rest mass of an electron is approx. `9.119xx10^-31*kg`, approx. 4 orders of magnitude difference. Should electron mass be ignored, we are not going to sacrifice too much accuracy.