The interaction of Y, Y-2, Mo, and Mo-2 with NH3 is Studied to understand the influence of the electronic configuration of the transition metal atoms and clusters on their reactions with ammonia. The interactions are investigated with the all-electron linear combination of Gaussian-type orbitals Kohn-Sham density functional theory (LCGTO-KS-DFT). The binding energies and harmonic frequencies characterize the equilibrium geometries. The reaction products investigated are MNH3, MNH, M2NH3, M2NH, and M-2(NH)(2). The binding energy indicates that the reaction of Y and Y-2 is possible. For Y, the stable products are YNH3 and YNH with binding energies of 24.6 and 32.6 kcal/mol, respectively. For Y-2, the stable products of the reaction are Y2NH3, Y2NH, and Y-2(NH)(2) (binding energies of 13.9, 55.5, and 110.2 kcal/mol, respectively). For Mo, the stable product is MoNH3 with a binding energy of 8.5 kcal/mol. For MoNH, the binding energies indicate that the reactants (Mo + NH3) are more stable than the products (MoNH + H-2) by 9.8 kcal/mol. For the Mo-2[NH3] complex, the binding energy is 17.9 kcal/mol, in good agreement with the experimental value of 14 kcal/mol previously reported. For Mo-2, there are no other stable products of the reaction because Mo2NH and Mo-2(NH)(2) are less stable than the reactants (Mo-2 + NH3) by 12.7 and 10.9 kcal/mol, respectively. The differences in the bonding are explained with molecular orbital pictures. For each metal, a relationship between the electronic configurations of the transition metals and the binding energies is reported.