Niels Bohr is a famous Danish scientist who first proved the incompatibility of the classical laws of physics and atoms. In this regard, he introduced two assumptions, now known as Bohr's quantum postulates. They rely on the atom model once proposed by E. Rutherford, according to which it (the atom) has a structure similar to that of the Universe: the electrons of the atom are in continuous motion around a stationary particle - the nucleus. At first, such a model was considered ideal and fully describing and explaining all experiments related to the atom. However, later it became clear that this model is not able to answer the question about the fact of the existence of an atom and its stability.
According to the planetary model, the movement of electrons around a fixed nucleus must certainly be accompanied by radiation of electromagnetic waves, whose frequency is equal to the frequency of rotation of negatively charged elements around the center. As a result, the electron energy must constantly decrease, which, in turn, leads to its greater attraction to the nucleus. However, experiments show that this does not happen. An atom is generally a stable system that can exist for a long period without exposure to outside influences. Atomic radiation can be called discrete, i.e. intermittent, which, of course, indicates the fact of the frequency of study, and not its constancy. In other words, scientists came to the conclusion that the application of the classical laws of physics to explain the existence of electrons is impossible.
Only in 1913 the assumptions introduced by Bohr made it possible to explain the principles of energy emission by electrons using the example of a hydrogen atom .
The conclusions made by Bohr were empirically confirmed by many scientists of that time. Based on his assumptions, a whole theory was created, which later became a special case of quantum mechanics. Bohr's postulates are as follows:
1. An atomic system radiates energy, conventionally called En, only being in quantum states. Otherwise (when the atom is in a stationary state), energy is not released.
In this case, the stationary state refers to the movement of electrons in certain orbits. Despite the actual presence of accelerated motion, electromagnetic waves are not radiated, the atom has only a quantum energy value.
2. The second postulate, most often known as the frequency rule, indicates that the transition of an atom from one state to another (usually from stationary to quantum) is accompanied by the release or absorption of energy. This process is carried out in small portions - quanta. Their value corresponds to the difference in the energy of states between which the transition actually occurs. The second postulate allows us to calculate the frequency of radiation of a hydrogen atom from known experimental values of the energies of stationary states.
Bohr's postulates are applicable to explain the absorption and emission of light by a hydrogen particle. Actually, it was in this way that Bohr himself once confirmed his conclusions. Bohr's postulates have allowed modern scientists to construct a theory of the spectrum of hydrogen. It is noteworthy that the construction of a quantitative theory of the spectrum of the next element - helium - turned out to be practically impossible.
Nevertheless, the postulates of Bohr - a physicist who laid a strong brick in the foundation of quantum theory, are still the most important observations and conclusions. In particular, it was possible to construct a theory of absorption and emission of light, which is impossible to make on the basis of data from only classical physics.
Bohr's postulates made it possible to breathe new life into classical mechanics. To this day, they remain undeniable within the framework of quantum mechanics.