A detailed study of the nucleation and growth of Cu on Ni(100) as a function of substrate temperature and deposition rate by variable temperature STM is reported. By the quantitative analysis of the saturation island density as a function of temperature and flux for submonolayer coverages, we have deduced the migration barrier (0.35 eV), the dimer bond energy (0.46 eV) as well the sizes of the the critical nuclei. Because the dimer bond energy is large with respect to the migration barrier, a well-defined transition from a critical nucleus of 1 to 3 has been observed, as expected from the adsorption site geometry on square lattices. The large dimer bond energy of Cu on Ni(100) is one of the physical reasons for the recently uncovered strain relief mechanism via internal {111} faceting. The substantially increased island density on mono-and bilayer copper films on Ni(100) with respect to multilayer films might also be attributed to the enhanced lateral bonding.