If P x y z d x d y d z is the probability of finding an electron in the volume element dx dy dz at the point of a molecular entity with coordinates x , y , z, then P x y z is the electron density at this point. For many purposes (e.g. X-ray scattering, forces on atoms) the system behaves exactly as if the electrons were spread out into a continuously distributed charge. The term has frequently been wrongly applied to negative charge population.