We all physicist have long been believed that an elementary particle is a wave as well as a particle, but we discuss in this paper that an electron (probably all fermions) is always a particle. Author claim that quantum mechanics (QM) is not such mysterious as Bohr stated that the wave turn to the particle by observation. We can understand QM by natural human sense. The wave nature of electrons is only an appearance or a phenomena but not intrinsic or substantial. An electron is an individual body, which interferes with other individual electrons. Interference is the key word instead of the wave to understand the quantum mechanics. Interference produces the wave nature and the uncertainty. When we determine that an electron is nothing but a particle, we will see the true meaning of wave function and the Schr?dinger’s equation.
‘Quantum mechanics’ shows how Bohr's old quantum theory was superseded by a newer theory of quantum mechanics. Bohr's quantum theory worked well in single electron sytems, but not in multi-electron systems. Quantum mechanics allowed the development of Schrödinger's equation, which could theoretically predict the determination of electron energy levels in any system. The advantage of quantum mechanics over quantum theory lies in its treatment of electrons as waves. This allowed Schrödinger to apply mathematical boundary conditions to his equation and quantise the energy levels of electrons. Further work by Heisenberg showed that electrons can be thought of as being spread around a shell rather than being in one place.