A covalent bond is a localised bond formed as a strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms.
Non-metals can exist as molecules formed from covalently bonded atoms or in the case of carbon and silicon giant covalent lattices.
Non-metal elements can combine to form covalent compounds.In a covalent bond, atomic s, p, d and f orbitals overlap to form molecular orbitals. Each atomic orbital contains a single electron.
The molecular orbital contains the shared pair of electrons. The shared electrons are attracted to the nuclei of each atom and this holds the two atoms together.
The bonded atoms usually have the same electron configuration as the noble gas at the end of the same period (but not always, for example in BF3 or PCl5). The average bond enthalpy measures the strength of a covalent bond. The greater the bond enthalpy the stronger the covalent bond.