A chemical bonding model for defects and defect precursors at Si-SiO2 interfaces is presented. Bonding geometries of neutral and charged Si-, O-, N-, and H-atoms are described in terms of the valence shell electron pair repulsion model, thereby identifying a qualitative distinction between charged (a) Si-atoms, and charged (b) O-, N-, or H-atoms. Threefold coordinated Si- atoms are stable in three charge states (+, 0, and -), and can be active as trapping and/or recombination centers depending on their charge state. In contrast, there is a direct relationship between charge state and bonding coordination for O-, N-, and H-atoms, and as such their roles in defect generation processes are qualitatively different. Reaction mechanisms based on these differences in local bonding are (i) discussed for the generation of defects comprised of threefold coordinated Si-atoms, and/or positively charged H-, O-, and N-atoms, with coordinations of two, three, and four, respectively, and (ii) compared with experiments.