The first phase we will discuss is the solid phase. Solids are characterized by their ability to maintain their shape. In a solid the particles are held in a fixed pattern by intermolecular forces. The molecules will vibrate in a fixed position, but will not move considerably from that position. Not all solids have a very regular or geometric pattern.
Many solids do have a regular or repetitive pattern, however, like salt, sugar, or diamond.
Some of these geometric patterns can be found in Figure 9.1 on the left. A solid with an orderly, three-dimensional pattern that repeats itself over and over again is classified as a crystal . Solids whose atoms are not arranged in any orderly and repetitive manner are classified as amorphous . Finally, composite solids are composed of several different materials bonded together. As a result of being able to maintain their shape, solids are also characterized by a fixed volume.