Atomic Bonding in Solids

Atomic Bonding in Solids
Three different types of primary or chemical bond are found in solids—ionic, covalent, and metallic. For each type, the bonding necessarily involves the valence electrons; furthermore, the nature of the bond depends on the electron structures of the constituent atoms. In general, each of these three types of bonding arises from the tendency of the atoms to assume stable electron structures, like those of the inert gases, by completely filling the outermost electron shell. Secondary or physical forces and energies are also found in many solid materials; they are weaker than the primary ones, but nonetheless influence the physical properties of some materials.

1. Ionic Bonding
Ionic bonding is perhaps the easiest to describe and visualize. It is always found in compounds that are composed of both metallic and nonmetallic elements. Atoms of a metallic element easily give up their valence electrons to the nonmetallic atoms. In the process all the atoms acquire stable or inert gas configurations and, in addition, an electrical charge; that is, they become ions. Sodium chloride (NaCl) is the classic ionic material. A sodium (Na 11) atom can assume the electron structure of neon(Ne 10) (and a net single positive charge) by a transfer of its one valence 3s electron to a chlorine atom (Cl 17). After such a transfer, the chlorine ion has a net negative charge and an electron configuration identical to that of argon (Ar 18). In sodium chloride, all the sodium and chlorine exist as ions. This type of bonding is illustrated schematically in Figure 1. The attractive bonding forces are coulombic; that is, positive and negative ions, by virtue of their net electrical charge, attract one another.