Using the classical valence bond description of the electron-pair bond, as a resonance between a covalent structure and two ionic structures, we study the change in the topology of the charge density at the bond critical point. In the first part of this paper, the density of the H-H and Li-H bonds is analyzed in terms of three types of contributions: ρ(A-B) = ρcov + ρres + ρion, the first contribution is due to the covalent structure, the second to the resonance between covalent and ionic structures, and the last one comes from the ionic structures. From this analysis, we conclude that when the bond is described as a covalent and one ionic structure, as in Li-H, the increase in the ionicity of the bond also corresponds with an increase in the closed-shell character of the electron density. However, in the case of the H-H bond, where the two ionic structures are equally important, the increment in the shared type interaction is due to the resonance between covalent and ionic structures. In the second part of this paper, we report an analysis of the classical valence bond description and the topological properties of the electron charge density calculated from ab initio GVB calculations for 15 different diatomic molecules at the equilibrium geometry and their dependence with the internuclear distance for H2, LiH, F2, Cl2, Li2, and Na2 molecules. This analysis reveals the importance of the overlap between the hybrid orbitals in a Heitler-London type wave function in determining the topological properties at the bond-critical point for covalent bonding. For Li2 we have found that at the equilibrium distance, the topology of ρ shows a maximum located at the middle of its bond, while for Cl2 a similar maximum is found at shorter internuclear distances.