Studies focusing on the functionalization of the surface of free silicon nanoparticles are presented. This functionalization is applied to hydrogen-terminated silicon nanoparticles to evaluate how far the well-known soln.-phase chem. of thermal-, radical-, Lewis acid- and UV light-mediated hydrosilylation can be applied to the surface chem. of silicon nanoparticles. The efficiencies of hydrosilylation for thermal-, radical- and Lewis acid-mediated reactions on silicon nanoparticles surfaces, deduced from the intensity of the n(Si-H) absorption, are found to be comparable.