Nucleation and growth of Pd on cleaved MgO(001) surfaces were studied by variable-temperature atomic force microscopy in the temperature range 200-800 K. Constant island densities (similar to 3x10(12)cm(-2)) were observed over a wide temperature range, indicating nucleation kinetics governed by point defects with a high trapping energy. These results are compared to a rate equation model that describes the principal atomistic nucleation and growth processes, including nucleation at attractive point defects. Energies for defect trapping, adsorption, surface diffusion, and pair binding are deduced, and compared with recent nb initio calculations.