# Question 3438c

For a simple treatment of atomic structure, see [here].(https://socratic.org/questions/why-do-all-isotopes-of-hydrogen-have-an-atomic-number-of-1216989)# But as to your question, the rest mass of an electron is $9.11 \times {10}^{-} 31 \cdot k g$. The rest mass of a proton (or a neutron, which also resides in the nucleus) is $1.67 \times {10}^{-} 27 \cdot k g$, and thus there are 3 orders of magnitude difference in terms of mass.