How do chemical reactions occur at the molecular level, and what theoretical frameworks underpin our understanding of these processes? From classical theories like Lewis structures and VSEPR theory to more contemporary models like molecular orbital theory and valence bond theory, explore the foundational principles guiding chemical reactivity. Investigate how factors such as bond formation, electron configuration, and molecular geometry influence reaction mechanisms. Additionally, consider how quantum mechanics provides insights into the behavior of atoms and molecules, enabling predictions of molecular behavior and the development of computational chemistry tools. How do these theories collectively contribute to our comprehension and manipulation of chemical systems?