We present a synthetic review of elementary chemical mechanisms source of the oxidation of pure silicon (100) surfaces. These mechanisms are then discussed from their ability to build a mesoscale model of the Kinetic Monte Carlo type dedicated to the process simulation of silicon thermal oxidation. We show that oxidation is driven by two main processes: (i) charge transfer arising from the formation of Si-O bonds in contact to pure silicon at the interface, (ii) destructive oxidation in which SiO building blocks rearrange at the interface to form a hexagonal-based oxide network directly in contact to cubic Si layers. Based on these considerations, simulations at the process scale exhibit epitaxial behavior within the interfacial domain. The resulting oxide layers are analyzed in terms of local to more extended defects. We observe two types of defects: (i) “intra-domain defects” which are related to local distortion of the elementary hexagonal oxide pattern Si6O6 (ii) “ inter-domain defects”, which are related to global oxide structural transitions from one orientation to another.