Packing structures of common ionic salts include FCC and BCC. The density of a crystal is inversely related to the equilibrium constant. The dissociation energy of a salt is large when the equilibrium...Packing structures of common ionic salts include FCC and BCC. The density of a crystal is inversely related to the equilibrium constant. The dissociation energy of a salt is large when the equilibrium separation distance is small. The densities and equilibrium radii for common salts (FCC) are nearly the same.