This book was originally intended as a review chapter, and this fact has strongly influenced the organization of the material. For example, there is no formal development of the various physical concepts that are introduced. Rather, emphasis is placed 011 a physical description of these concepts, and the analytic formalism is only summarized or referenced. Since the number of concepts that must be introduced is quite large, even for the treatment of so limited a topic, it is feared that some of them have been introduced too abruptly, as though arbitrarily invoked to explain some isolated phenomenon.
This failing is more apparent than real. The fact is that the existence of several competitive factors gives rise to a rich variety of physical manifestations, and emphasis has been placed on the interpretation of this richness in terms of defined factors that appear to operate in a similar manner over the whole range of crystalline materials, from ionic insulators to metals. The hope is that these
interpretations riot only support some of the extrapolations that are asserted, but also will provide the chemist with a physical intuition that can be fruitful for the design of materials with specified characteristics.