The O-Cl bond (the bond between oxygen and chlorine) is classified as a polar covalent bond. This classification comes from the difference in electronegativity between the two atoms involved in the bond.
Electronegativity is the measure of an atom’s ability to attract and hold onto electrons. Oxygen has a higher electronegativity (3.5 on the Pauling scale) compared to chlorine (3.0). This means that in an O-Cl bond, the electrons are not shared equally. Instead, the pair of electrons that are shared is pulled more towards the oxygen atom, creating a partial negative charge on the oxygen and a partial positive charge on the chlorine.
Since the difference in electronegativity is significant but not large enough to strip electrons entirely (which would result in an ionic bond), it demonstrates the characteristics of a polar covalent bond. Therefore, while the bond has both covalent and ionic characteristics, it is primarily considered polar covalent due to the unequal sharing of electrons and the resulting dipole moment.