We have carried out a thorough investigation of bonding and energetics in two different class of heteroatomic clusters viz. single impurity based LinSn (nless than or equal to9) clusters and mixed aluminum-based binary clusters Al4X4 (X = Be, Mg, B, Si). We employ first principle Born-Oppenheimer molecular dynamics within the framework of density functional theory using generalized gradient approximation. The bonding characteristics have been analyzed using electron localization function (ELF) along with charge density and valence molecular orbital pictures. The analysis of bonding through ELF reveals that in LinSn (nless than or equal to9) clusters there is a transition from ionic bond to a metallic bond through an intermediate ionic-metallic bond. On the other hand, it is found that Al4X4 (X = Be, Mg, B, Si) clusters show interesting characteristics of lone pairs on Al, polar covalent bonding, and a multicenter bonding. We demonstrate that ELF can play an important role in analyzing different types of bonding characteristics in heteroatomic clusters. (C) 2003 American Institute of Physics.