Hydrogen termination removes dangling bonds.  All surface Si atoms are tetrahedral. Hydrogen termination confers stability in ambient environments. So again, the surface is both clean (of oxides) and relatively inert. These materials can be handled in air without special care for several minutes.
The Si-H bond in fact is stronger than the Si-Si bonds.  Two kinds of Si-H centers are proposed, both featuring terminal Si-H bonds.  One kind of site has one Si-H bond.  The other kind of site features SiH centers.
Like organic hydrosilanes, the H-Si groups on the surface react with terminal alkenes and diazo groups. The reaction is called hydrosilylation. Many kinds of organic compounds with various functions can be introduced onto the silicon surface by the hydrosilylation of a hydrogen-terminated surface.  The infrared spectrum of hydrogen-terminated silicon shows a band near 2090 cm, not very different from νSi-H for organic hydrosilanes.