Relation between interatomic distances and sizes of ions in molecules and crystals

Bond lengths and dissociation energies in alkali halides and alkaline earth oxides and fluorides have been analysed. Ions are considered as static deformable spheres, where an essential part of the electron density is concentrated. In molecules, they are compressed. Moving from molecules to crystals, the bond lengths are extended to such an extent that closed electron shells of ions in alkali halide crystals are separated by distances of approximately 20 pm owing to weakened Coulomb attractive forces acting in opposite directions in a crystal. Short-range repulsion is important only within a few surface layers. Some ionic radii are approximately estimated.