Physical Revolution in Chemistry: the Core Ideas behind the Bohr Model of the Atom

Abstract

Niels Bohr published the fundamentals of the atom model later named after him in three scientific papers in 1913. This article explores the origins of the famous postulates in the model and also discusses how these were validated experimentally in later discoveries. The postulate that states the circular movement of the electron around the nucleus contradicted the Maxwell equations, which were well established in 1913 and required the emission of electromagnetic radiation in such cases. However, the assumed scenario followed directly from sound experimental findings. The truly novel element was the quantum postulate, which enabled a fully quantitative interpretation of the known atomic spectrum of the hydrogen atom. To establish the postulate, Bohr assumed a connection between the frequency of the circular motion of the electron and the frequency of the emitted electromagnetic radiation. At the time, the utility of this assumption was shown by the agreement of the conclusions drawn from it with experimental observations. The physical background of the quantum postulate was discovered later by seemingly remote findings: the wave-particle duality, the quantum mechanical uncertainty principle, and the experimental confirmation of the fact that the angular momentum of the photon is a constant that does not depend on its energy. In this sense, the postulates that were originally set up only to provide the framework for an atom model became the harbingers of later major developments in physics already given in the form of an exact mathematical equation.