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

The nucleus of the atom accounts for about 99.95% of the mass of the atom, with electrons contributing a very small portion.
This is why, for example, if we need to look up the molar mass of a sodium ion, $N {a}^{+}$, we are safe in using the atomic molar mass of sodium, with no "correction" necessary for the missing electron.