The nucleus is very small compared with the overall size of an atom. An atom has a radius of about 1 x 10-10 m, while its nucleus has a radius of about 1 x 10-14 m. This means the radius of the atom is about 10 000 times larger than the radius of its nucleus.
To picture this, imagine the nucleus enlarged to the size of a pea, about 1 cm across. On that scale the atom would be about 100 m across, which is roughly the length of a football pitch.
Because the nucleus is so small, most of the volume of an atom is empty space between the nucleus and the electrons. The electrons move through this space in their shells.
