Definition of Quantum Mechanics
Quantum mechanics is a branch of chemistry that deals with the study of the behavior of matter and light rays on the atomic as well as on subatomic particles. This explains the properties of the atoms, molecules, and their constituent particles i.e. electron, proton, neutron, quarks, etc. The interaction of these particles with each other and with EM radiations (visible light, X-rays, gamma rays) is also studied in this.
The ground state, excited states, and transition states of individual atoms and molecules are also studied in this. The wave-particle duality of the atomic and subatomic objects is being demonstrated through quantum mechanics.