What is the difference between crystalline and amorphous solids?
Although the heart of the difference between crystalline and amorphous solids occurs on the atomic level, there are several physical characteristics which can often indicate one type or the other. Crystalline substances have regular shapes, and form flat faces when they are cleaved or broken. When they are heated, crystalline solids melt at a definite temperature (unless they decompose before melting). The regularity of crystalline solids is due to the arrangement of structural units into an orderly array or lattice. A unit cell is the smallest repeating unit of a crystal and the smallest portion from which the structure of the crystal can be understood. Stacking unit cells together forms the crystal much as stacking bricks together forms a wall. The unit cells of diamond and graphite are shown in Figure 3.9. Figure 3.9 Unit Cells Most solids you encounter regularly –wood, papers, and plastics–are amorphous rather than crystalline solids. When amorphous solids are broken, curved and
