Density functional calculations have been performed on the ground-state, spin-conserving reactions between N2O and Sc, Ti, and V atom. We have defined a reaction coordinate (N-O bond distance) along which we have investigated the reaction mechanism. Smooth reaction curves and significant exothermicity for each reaction have been obtained. It has been demonstrated that electron transfer from the metal atoms to N2O is an essential ingredient of the mechanism. This facilitates the bending of the N2O molecule, the N-O bond weakening, and an O-(P-2) dissociation without surface crossing. Furthermore via 4s-3d hybridization occurring on the metal atoms the 4s(beta) electron is transferred to the dissociating O atom, thus connecting the reactant and product channels without any energy barrier on a single potential energy surface. It has been found that charge transfer from N2O toward the metal atom compensates the 3d(alpha) electron transfer donated by the metal atom, resulting in a net 4s(beta) electron transfer. We have found that when the number of 3d electrons equals 3 tin the case of vanadium), the reaction exhibits a mechanism different from the reactions with Sc or Ti, and this can be explained by considering the Pauli repulsion between the interacting orbitals. We have shown that the mechanism predicted in this work is in good accordance with the so-called electron-transfer model, whereas only elements of the so-called direct abstraction model can be invoked to account for the predicted mechanism.