Covalent Network Solids

Covalent network solids include crystals of diamond, silicon, some other nonmetals, and some covalent compounds such as silicon dioxide (sand) and silicon carbide (carborundum, the abrasive on sandpaper). Many minerals have networks of covalent bonds. The atoms in these solids are held together by a network of covalent bonds, as shown in Figure 1. To break or to melt a covalent network solid, covalent bonds must be broken. Because covalent bonds are relatively strong, covalent network solids are typically characterized by hardness, strength, and high melting points. For example, diamond is one of the hardest substances known and melts above 3500 °C.

Figure 1 . A covalent crystal contains a three-dimensional network of covalent bonds, as illustrated by the structures of diamond, silicon dioxide, silicon carbide, and graphite. Graphite is an exceptional example, composed of planar sheets of covalent crystals that are held together in layers by noncovalent forces. Unlike typical covalent solids, graphite is very soft and electrically conductive.

مواضيع ذات صلة

Crystal Defects

Properties of Solids

Molecular Solids

Metallic Solids

Ionic Solids

The Fundamental Types of Crystalline Solids

Interstitial Void Spaces

The FCC unit cell

The cubic close-packed structure

The Hexagonal closed-packed structure

Two choices for the third layer lead to two different close-packed lattice types

Close-packed lattices in three dimensions