Main Post:

An electron moves in a circular orbit around the nucleus. The angular momentum of an electron in its orbit is quantized. The emission or absorption of a photon is always followed by a change in an electron's energy when it makes a quantum hop from one orbit to another. The Bohr model of hydrogen was the first atomic structure model to explain atomic hydrogen's radiation spectrum successfully. The Rutherford nuclear model of the atom came before it. According to Rutherford's model, an atom is made up of a positively charged point-like nucleus that holds nearly all of the atom's mass and negative electrons that are situated away from the nucleus. The emission and absorption spectra of atomic hydrogen and hydrogen-like ions with low atomic numbers are explained by Bohr's model of the hydrogen atom. It was the first model to use a quantum number to describe atomic states and to propose the quantization of electron orbits within the atom. The development of quantum mechanics, which deals with many-electron atoms, was aided by Bohr's model.

Question from the main post:

Noting the quantization of electron orbits: can you discuss what was the basis for proposing this quantization? (Note that the answer relies on the electrons' dual wave-particle character).