Quantum chemistry is a branch of chemistry that uses 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 properties and reactions. By applying mathematical models, scientists can predict the structure and energy of molecules. This field combines concepts from both quantum physics and chemistry to explain phenomena that classical chemistry cannot, such as the formation of chemical bonds and the behavior of electrons in different states. Quantum chemistry plays a crucial role in areas like material science, pharmaceuticals, and nanotechnology.