the bond becomes ionic. Figure 8.12: The relationship between the ionic character of a covalent bond and the electronegativity difference of the bonded atoms. Polarity • A molecule, such as HF, that has a center of positive charge and a center of negative charge is said to be polar, or to have a dipole moment. δ+ δ− H F Dec 01, 2003 · The formation of the hydrogen bond is investigated in terms of the charge density. The water dimer is chosen as an example, and the redistribution of the electrons due to the H-bond is discussed. The density difference between interacting and non-interacting monomers is partitioned using localized orbitals and localized partial densities.