Chemistry
Properties of Covalent Network Solids: Diamond
Quick fact
Diamond is the only gemstone made of a single element: carbon. Its hardness on the Mohs scale is 10, the maximum, and it can only be scratched by another diamond.
Why this is interesting
You know diamond is the hardest natural material, but did you know its extraordinary strength comes from the same type of bonds that hold water molecules together? So why is diamond so much harder than ice?
Read the full explanation
Understanding Properties of Covalent Network Solids: Diamond
In a covalent network solid like diamond, atoms are linked by strong covalent bonds in a three-dimensional, repeating pattern. Think of it as a single, enormous molecule. In diamond, each carbon atom forms four covalent bonds with neighboring carbon atoms, arranged in a tetrahedron. This means every carbon is connected to four others, and those connect to four more, forming an extended, rigid network. Because all these bonds are strong and directional, any attempt to break or deform the solid requires breaking many covalent bonds at once. That is why diamond is so hard and why it melts at an extremely high temperature (about 3550°C). Additionally, all valence electrons are locked in bonds, so there are no free electrons to carry an electric current—making diamond an electrical insulator.
A deeper explanation
The key to understanding the properties lies in the tetrahedral bonding geometry of sp³ hybridized carbon atoms. Each covalent bond is strong (about 347 kJ/mol) and highly directional, meaning atoms are locked into specific positions. To melt or deform diamond, you must overcome these bonds throughout the entire crystal. This contrasts with graphite, where carbon atoms form flat sheets held by weak forces, making it soft and electrically conductive. The same principle applies to other covalent network solids like silicon carbide (carborundum) or silicon dioxide (quartz), whose hardness and high melting points also derive from extensive covalent bonding. This concept matters because it explains why certain materials are chosen for drill tips, abrasives, and high-temperature applications—properties rooted in the network of covalent bonds.