# Electrons and Atomic Mass

Is the mass of electrons covered when talking about atomic mass. For example, the mass of Carbon is $$12.011\space\text{amu}$$. If this is including the mass of electrons (assuming the atom is neutral) the nucleus' mass is $$12.011-6(\frac{1}{1840})=12.00773913$$

The reason I need to know is I'm studying mass defect in relation to protons and neutron. If I inadvertently include electrons in my calculation, my binding energy will also be wrong.

• Good question. The mass of electron is so small relative to neutrons/protons that it can be neglected in binding energy calculations. Electron mass in amu is 0.00054. You can try both approaches and see the differences. – M. Farooq Nov 20 '19 at 3:42
• Note that 12.011 amu is the weighted isotope average mass. The mass of a neutral carbon-12 atom in the ground state (electronic and nuclear) is 12.0 amu (exactly), defining the amu. So, yes, it includes the mass of the 6 electrons. – Jon Custer Nov 20 '19 at 14:19
• (And, it is kind of funny that this was asked by a user named 'Dalton' - you'd think they would know their own definition!). – Jon Custer Nov 20 '19 at 14:20