Quantum chemistry is a branch of chemistry that applies the principles of quantum mechanics to understand the behavior of atoms and molecules. It focuses on how electrons interact within atoms and how these interactions influence chemical bonding and reactions. By using mathematical models and computational methods, quantum chemistry helps predict the properties of substances and the outcomes of chemical processes. This field is essential for explaining phenomena that classical chemistry cannot, such as the stability of molecules and the nature of chemical bonds. Key concepts include wave functions, quantum states, and energy levels, which provide insights into the microscopic world of matter.