ABSTRACT
The structure of materials in¨uences their behavior and properties. Therefore, understanding this structure helps to make appropriate selection of these materials for specic applications. Depending on the manner of atomic grouping, materials are classied as having molecular, crystal, or amorphous structures. In molecular structures, atoms are held together by primary bonds. They have only weak attraction. Typical examples of molecular structure include O2, H2O, and C2H4 (ethylene). Each molecule is free to act independently, so these materials possess relatively low melting and boiling points, since their molecules can move easily with respect to each other. These materials tend to be weak. Solid metals and alloys and most minerals have crystalline structure, where atoms are arranged in a regular geometric array as a lattice of a unit building block that is repetitive throughout the space. In an amorphous structure, such as glass, atoms have a certain degree of local order but lack the periodically ordered arrangement of the crystalline solid.
