The structures of intermetallic phases are not only governed by the number of valence electrons but also by their degree of localization and the transfer of electrons between the constituents. As a consequence, structures can considerably deviate form close packing, a fact that is not yet unterstood, even for metallic elements like Zn and Cd. Such unconventional bonding properties must, however, be reflected in the charge density distribution. For measuring this quantity by diffraction experiments with high- and medium-energy synchrotron radiation, high purity and high quality crystals of the compounds have to be synthesized and grown. The experimental electron density and its topological properties are to be compared with the results of accurate quantum chemical calculations, considering density functional and wave function based methods including electron correlation. The interpretation of the chemical bonding as derived from the experimental electron density, from ab initio band structure calculations and bonding indicators like the Electron Localization Function (ELF) will be related to results from angular resolved photo-electron spectroscopy as well as from Compton scattering experiments. First examples to be investigated are the element structures of Zn and Cd both of which crystallize with the symmetry of hexagonal close packing, but with c/a ratios that drastically deviate form the ideal value of 1.633. The perception obtained from these studies will be transfered to the investigations of different families of intermetallic compounds.
