In covalent bonding, a stable electron configuration is created by sharing of electrons between neighbouring atoms. Two atoms that are covalently bonded will share at least one electron from each atom.

The electrons are shared between atoms within in a 3D structure where the bonds are highly directional. This directionality dictates the atomic packing.

a) Covalent bonding in methane, b) Diamond atoms sharing electrons.

In diamond, the carbon atoms build up into a 3D array with the bonds pointing towards the corners of a tetrahedron. 

Covalent bonds can be very stiff and generally give a material with a:

  • very high elastic modulus
  • high (inherent) strength1
  • high melting point
  • low electrical conductivity

Covalent bonding is the dominant bonding found in silicate ceramics and glasses. It also occurs in the backbone of polymer chains and in the cross-links in thermosetting polymers.

1. The inherent strength is high but in practice the strength can be low because of the brittle nature of the material.