Atomic dimensions. Computer artwork showing the relative sizes of atoms and their components. The scale at bottom, measured in fractions of a metre, decreases from left to right. A large water drop (blue, at upper left) is about 1 cm (10-2 metres) in size. Next in size is a molecule (red, green & blue) at about 1 nanometre (10-9 m) and an atom with its orbiting electrons at 1 angstrom (10-10 m). The neutrons (blue) and protons (red) which form the atomic nucleus (10-14 m) are about 1 femtometre (10-15 m) in size. Electrons (green) are roughly an attometre (10-18 m) in size as are the up (arrow up) and down (arrow down) quarks from which neutrons and protons are formed.