CHAPTER ONE - The Crystalline State

Abstract

This chapter describes networks of points in space, or space lattices, such that each point is similarly placed in relation to the rest. It is useful to do so because these lattices underlie the placing of atoms in crystalline substances and are used to define and classify them. The chapter also focuses on the general lattice, the seven primitive lattices, the 14 bravais lattices and crystalline solids. A particular chemical substance is crystalline when an identical unit group of atoms, characteristic of the substance, similarly replaces each point of a bravais lattice. Thus, it is a substance in which each atom has the same surroundings as every other—the only way of ensuring that each part has the properties of the whole. The substance is said to have a crystal structure defined by the size and shape of its unit cell and by the nature and positions of the atoms in its unit group. The unit group in its simplest form is merely one atom, as in several elements. The unit group in its next simplest form consists of two like atoms, as in the metals beryllium and magnesium.