About 99.999% of the mass and solid matter in an atom is in its nucleus, which only takes up one quadrillionth of the atom’s space. How small is that? Imagine scaling an atom up to the size of a basketball arena. The nucleus is a grain of sand floating in the middle of the arena — and the mass of the whole atom is the same as the mass of the grain of sand. (The diameter is calculated from the van der Waals radius.)
Keishinrei 