Structure of Metals
The arrangement of atoms in a material determines the behavior and properties
of that material. Most of the materials used in the construction of a nuclear
reactor facility are metals. In this chapter, we will discuss the various types of
bonding that occurs in material selected for use in a reactor facility. The
Chemistry Handbook discusses the bonding types in more detail.
STATE the five types of bonding that occur in materials and
Matter, as we know it, exists in three common states. These three states are solid, liquid, and
gas. The atomic or molecular interactions that occur within a substance determine its state. In
this chapter, we will deal primarily with solids because solids are of the most concern in
engineering applications of materials. Liquids and gases will be mentioned for comparative
Solid matter is held together by forces originating between neighboring atoms or molecules.
These forces arise because of differences in the electron clouds of atoms. In other words, the
valence electrons, or those in the outer shell, of atoms determine their attraction for their
neighbors. When physical attraction between molecules or atoms of a material is great, the
material is held tightly together. Molecules in solids are bound tightly together. When the
attractions are weaker, the substance may be in a liquid form and free to flow. Gases exhibit
virtually no attractive forces between atoms or molecules, and their particles are free to move
independently of each other.
The types of bonds in a material are determined by the manner in which forces hold matter
together. Figure 1 illustrates several types of bonds and their characteristics are listed below.
Ionic bond - In this type of bond, one or more electrons are wholly transferred
from an atom of one element to the atom of the other, and the elements are held
together by the force of attraction due to the opposite polarity of the charge.
Covalent bond - A bond formed by shared electrons. Electrons are shared when
an atom needs electrons to complete its outer shell and can share those electrons
with its neighbor. The electrons are then part of both atoms and both shells are