a An atom has a diameter of 2.00 A and the nucleus of that atom has a diameter of 8.50 x 10-5 . Determine the fraction of the volume of the atom that is taken up by the nucleus. Assume the atom and the nucleus are a sphere. fraction of atomic volume: Calculate the density of a proton, given that the mass of a proton is 1.0073 amu and the diameter of a proton is 1.70 x 10-15 m. density: g/cm