Question

Most of the mass of the atom is provided by what?

Answer 1

The nucleus of the atom accounts for about `99.95%` of the mass of the atom, with electrons contributing a very small portion.

Explanation:

We know that the proton and neutron have very similar masses (though not identical!) and that each outweighs the electron by nearly a 2000:1 ratio.

So, the nucleus is the location of virtual all the mass of the atom.

This is why, for example, if we need to look up the molar mass of a sodium ion, `Na^+`, we are safe in using the atomic molar mass of sodium, with no "correction" necessary for the missing electron.