Slide 10 of 18
This model dates from about 1915, when Bohr was working with Rutherford.
Bohr assumed the electron is attracted to the proton in the hydrogen atom electrostatically, by Coulomb’s Law, and that it moved in a circular orbit, according to F=ma, with the electrostatic force as centripetal force.
His crucial, ad hoc, quantum assumption was that the angular momentum was quantized. This meant the electron could occupy only certain orbits, each one characterized by an integer “quantum number.”