A covalent bond is a very strong attraction between two or more atoms that are sharing their electrons. In structural formulas, covalent bonds are represented by a line drawn between the symbols of the bonded atoms.
Localized Covalent Bond
A localized covalent bond describes the mutual electrostatic attraction of two adjacent nuclei for a shared pair of electrons which occupy the same molecular energy level.
Delocalized Covalent Bond
A delocalized covalent bond describes the electrostatic attraction of more than two nuclei for a shared pair of electrons which occupy the same molecular energy level.