In a covalent bond, electrons are shared between atoms. This means that the electrons are not localized to a single atom, but instead move around both atoms in the bond. The electrons in a covalent bond are said to be delocalized.

Delocalization of electrons is what gives covalent bonds their strength. The more delocalized the electrons are, the stronger the bond. This is because delocalization of electrons increases the overlap between the atomic orbitals of the atoms involved in the bond. The greater the overlap, the stronger the bond.

Covalent bonds are the strongest type of chemical bond. They are found in many different types of molecules, including molecules of water, carbon dioxide, and methane.