What type of covalent bond is characterized by an unequal sharing of electrons between atoms?

A polar covalent bond is characterized by an unequal sharing of electrons between atoms. This occurs when the two atoms involved in the bond have different electronegativities, which is a measure of how strongly an atom attracts electrons. In a polar covalent bond, the atom with higher electronegativity attracts the shared electrons more strongly, leading to a partial negative charge on that atom and a partial positive charge on the other atom. This distinct separation of charge imparts polarity to the molecule, making it interact differently with other molecules, especially in biological systems.

In contrast, a nonpolar covalent bond involves equal sharing of electrons between atoms that have similar electronegativities, resulting in a balanced distribution of electrical charge. An ionic bond, on the other hand, involves the transfer of electrons from one atom to another, leading to the formation of charged ions that attract each other due to opposite charges. A hydrogen bond is not a true covalent or ionic bond but rather a weak attraction between a hydrogen atom covalently bonded to an electronegative atom and another electronegative atom.