What is the size of an atom and the ratio of the size of the nucleus to the electron cloud?

The size of an atom is in the tenths of nanometres (0.0000000001 m), and the nucleus is even 100,000 times smaller. From this ratio and the fact that the mass of protons is approximately 2,000 times greater than the mass of electrons, among other things, it follows that 99.999% of an atom is actually empty space.

If we considered a poppy seed (approximately 1 mm in diameter) as the nucleus, the size of the atom (electron shell) would be 100,000 times larger—approximately 100 m. That corresponds to the length of a football field. We can therefore imagine an atom as a poppy seed placed in the centre of a football field.

The dimensions of an electron are more complicated — they are so small that we cannot see them even with an electron microscope (in principle). They are believed to be smaller than 10—19 m, which is again roughly 100,000 times smaller than the nucleus of an atom. If we took a grain of poppy seed as an electron, the nucleus would be the size of a football field, so the entire atom would have a diameter of 10,000 km and an area roughly equivalent to the combined area of Europe and Africa.