Bohr's theory of hydrogen atom is a semi-classical theory that expounds the structure of hydrogen atom. It was put forward by N Bohr in 19 13 by combining M Planck's quantum concept, Rydberg-Ritz combination principle and E Rutherford's nuclear structure model. The basic assumptions of Bohr's theory are as follows: ① The electrons outside the nucleus can only move in a series of steady-state orbits without radiation, and this special mechanical equilibrium state can be treated by classical mechanical methods. (2) Radiation (or absorption) occurs when an atom transitions from a steady state with energy Ei to another steady state with energy Ef. At the beginning and end of the transition, the relationship between the radiation frequency v and the two steady-state energies is determined by the following formula:

|Ei-Ef|=hv .

According to Bohr's basic hypothesis, the formulas of Balmer system, Paschen system, Lyman system, brala system, discoverer system and Humphrey system of hydrogen atom spectrum can be derived.

Bohr also assumed that the interaction between electrons and nuclei was mainly coulomb force. Bohr believed that electrons move in a circle around the nucleus.

Bohr's theory broke through the classical concepts and put forward some extremely important concepts, such as steady state, quantization condition, discrete energy levels, energy level transition, etc., which theoretically explained the empirical law of hydrogen atom spectrum for the first time and made great achievements. On the other hand, Bohr's theory is still not free from the shackles of classical theory, so it has great limitations. The correct theory should be based on quantum mechanics.

In fact, according to quantum mechanics, when an atom is in a steady state, its probability density does not change with time. The charge density of an atom is determined by its probability density and the charge amount of an electron. A stable charge distribution system will not produce electromagnetic radiation, so atoms will not radiate electromagnetic waves when they are in a steady state. In the process of atomic transition, it is known that the probability density will oscillate with time, and the frequency is v=|Em-En|/h, which is exactly the same as that given by Bohr theory. The oscillation of probability density with time means that the probability of finding electrons around will oscillate with time, so the charge distribution of atoms will also oscillate with time, and atoms will of course radiate. In this way, we have satisfactorily explained the internal mechanism of electromagnetic wave radiation (absorption) during atomic transition.