The nature of the chemical bonding in the 1:1 complexes formed by the fourth period transition metals (Sc, Cu) with 14 electrons (N-2, CN-, C2H2) and 10 electrons (NH3, H2O, F-) ligands has been investigated at the ROB3LYP/6-31 1+G(2d) level by the ELF topological approach. The bonding is ruled by the nature of the ligand. The 10 electrons and anionic ligands are very poor electron acceptors and therefore the interaction with the metal is mostly electrostatic and for all metal except Cr the multiplicity is given by the [Ar]c(n) configuration of the metallic core (n = Z - 20). The electron acceptor ligands which have at least a lone pair form linear or bent complexes involving a dative bond with the metal and the rules proposed previously for monocarbonyls (J. Pkys. Chem. A 2003, 107, 4506) hold. In the case of ethyne, it is not possible to form a linear complex and the cyclic C-2 upsilon structure imposed by symmetry possesses two covalent M-C bonds, therefore the multiplicity is given by the local core configuration [Ar]c(n) for all metals except Mn and Ni.