Metal halides structures and energetics

All the halides of the alkali metals have NaCl or CsCl structures (Figs. 6.16 and 6.17) and their formation may be considered in terms of the Bom-Haber cycle (see Section 6.14). In Section 11.5, we discussed trends in lattice energies of these halides, and showed that lattice energy is proportional to / r+ + r ). We can apply this relationship to see why, for example, CsF is the best choice of alkali metal fluoride to effect the halogen exchange reaction 17.18. 

In the absence of solvent, the energy change associated with 

A few other monohalides possess the NaCl or CsCl stracture, e.g. AgF, AgQ, and we have already discussed (Section 6.15) that these silver(I) halides exhibit significant covalent character. The same is true for CuCl, CuBr, Cul and Agl which possess the wurtzite structure (Fig. 6.21). 

For metals exhibiting variable oxidation states, the relative thermod5mamic stabilities of two ionic halides that contain a common halide ion but differ in the oxidation state of the metal (e.g. AgF and AgF2) can be assessed using Bom—Haber cycles. In such a reaction as 17.19, if the increase in ionization energies (e.g. M — M versus M — M ) is approximately offset by the difference in lattice energies of the compounds, the two metal halides will be of about equal stability. This commonly happens with (/-block metal halides. 

M — M ) is approximately offset by the difference in lattice energies of the compounds, the two metal halides will be of about equal stability. This commonly happens with (i-block metal halides. 

A few other monohalides possess the NaCl or CsCl structure, e.g. AgF, AgCl, and we have already discussed (Section 5.15) that these compounds exhibit significant 

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