Non-contact atomic force microscopy has driven the development of a variety of exciting chemomechanical protocols for manipulating metal, semiconductor, and insulating surfaces at the single chemical bond limit. In this chapter we discuss atomic manipulation on silicon surfaces via mechanical force alone (mechanochemistry), with a particular focus on a prototype of a mechanicallyactuated atomic switch: the flipping of bi-stable dimers on the Si(100)–c(4 × 2) surface. The importance of the mutual orientation of electronic orbitals in the dimer manipulation process is explored in the broader context of the mechanochemical modification of covalently bonded semiconductors. In addition, variations in surface reactivity play a key role in the ability to generate (and image) atomic-scale modifications and we discuss experimental and theoretical work on H:Si(100) as an exemplar of a passivated and chemically inert substrate, as compared to the relatively high reactivity of the unpassivated Si(100) surface.