Introduction

The solid state is one of the three common states of matter, and it stands apart from liquids and gases because the particles that make up a solid -- atoms, ions or molecules -- are held together by strong interparticle forces of attraction. This gives solids a definite shape and a definite volume that change only slightly with temperature or pressure, unlike gases (no fixed shape or volume) or liquids (fixed volume, no fixed shape). In a solid the constituent particles are not free to move about; they can only vibrate about fixed mean positions, which is exactly why solids resist compression and retain their shape. Throughout this chapter, whatever the actual identity of the constituent particle -- an atom, an ion, or a molecule -- it will simply be called a 'particle' for convenience while describing the arrangement and packing of solids.