The bond formation between a cation X+ and an electron donor D is examined as a function of the electron acceptor capability of X+ with topological electron density analyses at the RHF and MP2 levels. Atom populations and atom dipoles are important for the description of dative bond formation. Dative bond formation is manifested primarily in the anisotropy of the donor basin for weak acceptors X while charge transfer becomes important for stronger acceptors. Other population analyses allow for the estimation of bond polarity but neglect the importance of atom polarities. The different stages of dative bond formation are exemplified by analysis of the electron density distributions of heterosubstituted diazonium ions (X-N2)+ with different acceptors X and by analysis of charge transfer and of atom anisotropies as a function of progressing X-N bond formation. Various Lewis structures are discussed as representations of the electron density distributions resulting from X-N bonding. The consideration of X-N nonconnected Lewis structures is required to adequately represent the electron density distributions. Atom anisotropies also play an important role for the correct appreciation of electron correlation effects on the basis of integrated atomic properties.