Introduction

Relating properties of substances to their structures has been a major objective of modern chemistry and this also happens to be a prime concern of solid state chemists. Some of the aspects of importance in solid state chemistry are electronic, magnetic, superconducting, dielectric and optical properties. We shall briefly discuss these properties and present highlights in the solid state chemistry of some interesting classes of materials. An important class of materials is that of ferroics, which possess several orientation states that can be switched from one to another by the application of an appropriate force; ferroelectric materials form a subgroup of this class of materials. Other classes of materials discussed are amorphous solids, mixed-valence compounds, low-dimensional solids and liquid crystals which are of considerable importance. We have also devoted attention to different types of metal-nonmetal transitions and have briefly examined the question, ‘what makes a metal?’. While a detailed discussion of the theory of electronic structure would be outside the scope of the book, we have presented the necessary background material at an elementary level and discussed some of the typical results obtained from empirical theory as well as electron spectroscopy.

Electrons in solids

In order to correlate the structure and physical properties of solids, it is essential to have a description of valence electrons that bind the atoms in the solid state. Two limiting descriptions of atomic outer electrons in solids are available: the band theory and the localized-electron theory or the ligand-field theory.