Lattices, and efficiency of packing

Crystal Reid stabilization energy (CFSE), 399—401, 408-413 Crystal lattices, and efficiency of packing, 118-122 Crystallography, 74-85 Crystals, imperfections in, 263-265... 

I describe the arrangement of atoms in the common cubic crystal lattices and calculate the packing efficiency for a lattice. 

With larger cations, such as cesium, the radius ratio (rCl /rcl-= 181 pm/ 167 pm = 1.08) increases beyond the acceptable limit for a coordination number of 6 the coordination number of the cations (and anions) increases to 8, and the cesium chloride lattice (Fig. 4.1b) results. As we have seen, although this is an efficient structure for cations and anions of about the same size, it cannot be directly related to a closest packed structure of anions... 

The overall lattice energies of ionic solids, as treated by the Born-Lande or Kaputin-skii equations, thus depends on (i) the product of the net ion charges, (ii) ion-ion separation, and (iii) packing efficiency of the ions (reflected in the Madelung constant, M, in the Coulombic energy term). Thus, low-melting salts should be most... 

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