The origin of the postulates in the Bohr model of the hydrogen atom

Abstract This lecture text introduces the Bohr model of the hydrogen atom in a historical context. Danish physicist Niels Henrik David Bohr introduced this model in a series of three scientific articles in 1913. The model was originally formulated on the basis of five explicit assumptions, which have been re-formulated as two postulates in modern chemistry textbooks. This contribution points out that the assumption of the absence of electromagnetic radiation in a system containing moving charges was a direct violation of Maxwell equations but, in fact, simply stated what had already been firmly established in experimental observations. The quantization condition, which said that the angular momentum of the electron is an integer multiple of h /(2π), was validated in the model by demonstrating that this leads to a theoretical prediction of the atomic spectrum of hydrogen that is in full agreement with the experimental results. In hindsight, this postulate seems to be the core achievement and was later justified in three independent discoveries: the wave–particle duality of de Broglie, the uncertainty principle of Heisenberg, and the direct detection of the angular momentum of the photon by Raman and Bhagavantam.