The unit cell for fe3o4 (feo-fe2o3) has cubic symmetry with a unit cell edge length of 0.839 nm. if the density of this material is 5.24 g/cm3, compute its atomic packing factor. the ionic radii of fe2+, fe3+ and o2- are 0.077 nm, 0.069 nm and 0.140 nm, respectively. in addition, the atomic weights of iron and oxygen are, respectively, 55.85 g/mol and 16.00 g/mol.