Question

Question #3438c

Answer 1

The mass of an atom, any atom is concentrated in its nucleus.

Explanation:

For a simple treatment of atomic structure, see [here].(https://socratic.org/questions/why-do-all-isotopes-of-hydrogen-have-an-atomic-number-of-1`216989)` But as to your question, the rest mass of an electron is `9.11xx10^-31*kg`. The rest mass of a proton (or a neutron, which also resides in the nucleus) is `1.67xx10^-27*kg`, and thus there are 3 orders of magnitude difference in terms of mass.

And thus electronic mass may be ignored given this disparity.