The understanding and control of silicon surfaces is of great importance in the production of silicon-based electronic devices made from semiconductor materials and constructed on silicon single-crystal substrates. This is the first study to see the effect of surface etching by fluorine on the stability of the unreconstructed Si(100) surface using periodic density functional calculations. All the possible fluorine substitution sites are considered, and the results are compared with the existing experimental observation in terms of suitability of fluorine substitution on the surface. The results are compared with H-terminated surfaces to prove the efficiency of fluorine in stabilizing the unreconstructed Si(100) surface. Oxidation of the Si(100) surface for both H- and F-terminated surfaces were also studied to propose the plausible mechanism of oxidation. Two kinds of experimental situations were mimicked for oxidation; (1) oxidation on the surface, i.e., generation of the Si-O-H bond, and (2) oxidation on the bridging bond between two silicons, i.e., generation of Si-O-Si, were compared to show the feasibility of Si-Q-Si bond formation. Oxidation through atomic oxygen was followed throughout the calculation. The calculations were performed with smaller clusters using density functional methodology to validate and rationalize the current understanding. The results were further supported by molecular electrostatic potential maps generated from periodic density functional calculation results.