Final answer:
A covalent chemical bond involves the sharing of electrons between two nonmetal atoms, either equally for nonpolar bonds or unequally for polar bonds. It forms when atoms share pairs of valence electrons to complete their valence shells, in contrast to ionic bonds where electrons are transferred.
Step-by-step explanation:
A covalent chemical bond is one in which electrons are shared equally by two atoms when the bond is nonpolar, or shared unequally when the bond is polar. In a covalent bond, two atoms share one or more pairs of valence electrons. The formation of a molecule consisting of two or more nonmetal atoms involves this type of bond, where shared electrons are attracted to the nuclei of both atoms.
For instance, a single covalent bond is formed when two electrons are shared, one from each atom. Similarly, a double covalent bond occurs when four electrons are shared, two from each atom.
Differences in electronegativity between the bonded atoms can lead to unequal sharing of electrons, resulting in a polar covalent bond. However, if there is a complete transfer of electrons from one atom to another, it is not a covalent bond but an ionic bond.