Covalent bonds are formed by sharing electrons between atoms. Specifically, in a covalent bond, atoms share pairs of electrons to achieve a stable full outer electron shell, which increases their stability. This sharing can be equal, as in atoms of the same element, or unequal, resulting in polar covalent bonds when atoms have different electronegativities. Unlike ionic bonds where electrons are given or taken, covalent bonds involve this mutual sharing to form stable molecules.
