In a polar covalent bond, the electrons are shared unevenly between the two bonded atoms. This means that the electrons, which are constantly moving, spend more time with the one atom than the other. Only the outer most electrons, known as valence electrons, are involved in polar covalent bonds.
Polarity occurs because one of the atoms in a covalent bond has a greater electronegativity than the other, which makes it attract the shared electrons more strongly. The uneven sharing of the electrons creates a dipole shift, which means that the side with the more electronegative atom has a slightly negative charge and the end with the less electronegative atom has a slightly positive charge.
Polar covalent bonds have unique properties due to their polarity. The slight charges associated with the dipole moment can cause intermolecular forces and interactions such as hydrogen bonding, where the slightly positively charged hydrogen atoms in polar molecules such as water can attract and weakly bond to the slightly negatively charged portions of other polar molecules. This phenomenon gives water and ice their physical properties and gives water dissociating solvent properties. Polar molecules dissolve more readily in water than nonpolar molecules because of the dipole intermolecular forces present in polar molecules.