Packing of particles in crystal lattice

The constituent particles of a crystalline solid are close packed -- they are arranged as tightly together as possible, which maximises the attractive interactions between neighbouring particles. When describing this packing, individual particles are treated as hard, incompressible spheres. A key measure of how tightly the spheres are packed is the coordination number: the number of neighbouring spheres that touch any one given sphere. The larger the coordination number, the more closely the spheres are packed around each other, so coordination number serves as a direct measure of the compactness of a close-packed structure. The sections that follow build up close packing step by step, starting from a simple one-dimensional row of touching spheres, moving …