In every atom the positive charge and mass are densely concentrated at the centre of the atom which is called the nucleus of the atom.

The dimensions (radius) of a nucleus are much smaller than those of an atom.

Experiments on scattering of $\alpha$-particles demonstrated that the radius of a nucleus was smaller than the radius of an atom by a factor of about $10^{4}$.

$\frac{\text { Volume of nucleus }}{\text { Volume of atom }}=\frac{4 / 3 \pi \times\left(10^{-14}\right)^{3}}{4 / 3 \pi \times\left(10^{-10}\right)^{3}}=10^{-12}$

$\therefore$ The volume of a nucleus is about $10^{-12}$ times the volume of the atom.

Even so the nucleus contains most (more than $99.9 \%$ ) of the mass of an atom. If we think of a atom is enlarged to the size of a classroom, the nucleus would be the size of pinhead.

Hence, the empty in the atom is a very large area.