What defines a polar covalent bond?

A polar covalent bond is characterized by the unequal sharing of electrons between two atoms, resulting in a distribution of charge that creates partial positive and negative charges. This arises when the atoms involved in the bond have different electronegativities, meaning one atom attracts the shared electrons more strongly than the other. As a result, the atom with higher electronegativity gains a partial negative charge, while the other atom, which has a lower electronegativity, acquires a partial positive charge. This phenomenon leads to the formation of a dipole moment in the molecule, which is the distinguishing feature of polar covalent bonds.

In contrast, a bond formed when two atoms share electrons equally would be classified as a nonpolar covalent bond, not a polar one. A complete transfer of electrons characterizes ionic bonds rather than polar covalent bonds. Metallic bonds involve the attraction between free electrons and metal ions, which is a different type of bonding altogether and does not pertain to covalent bonding. Thus, the correct definition aligns specifically with how the unequal sharing of electrons creates partial charges, defining a polar covalent bond.