Solids have greater interatomic attractions than liquids and gases. However, there are wide variations in the properties of solid materials used for engineering purposes. The properties of materials depend on their interatomic bonds. These same bonds also dictate the space between the configuration of atoms in solids. All solids may be classified as either amorphous or crystalline.

Amorphous

Amorphous materials have no regular arrangement of their molecules. Materials like glass and paraffin are considered amorphous. Amorphous materials have the properties of solids. They have definite shape and volume and diffuse slowly. These materials also lack sharply defined melting points. In many respects, they resemble liquids that flow very slowly at room temperature.

Crystalline

In a crystalline structure, the atoms are arranged in a three-dimensional array called a lattice. The lattice has a regular repeating configuration in all directions. A group of particles from one part of a crystal has exactly the same geometric relationship as a group from any other part of the same crystal.

Summary

The important information in this chapter is summarized below.

Bonding Summary

Types of Bonds and Their Characteristics

Ionic bond - An atom with one or more electrons are wholly transferred from one element to another, and the elements are held together by the force of attraction due to the opposite polarity of the charge.

Covalent bond - An atom that needs electrons to complete its outer shell shares those electrons with its neighbor.

Metallic bond - The atoms do not share or exchange electrons to bond together. Instead, many electrons (roughly one for each atom) are more or less free to move throughout the metal, so that each electron can interact with many of the fixed atoms.

Molecular bond - When neutral atoms undergo shifting in centers of their charge, they can weakly attract other atoms with displaced charges. This is sometimes called the van der Waals bond.

Hydrogen bond - This bond is similar to the molecular bond and occurs due to the ease with which hydrogen atoms displace their charge.

Order in Microstructures

Amorphous microstructures lack sharply defined melting points and do not have an orderly arrangement of particles.

Crystalline microstructures are arranged in three-dimensional arrays called lattices.