Niels H. D. Bohr

From the Nobel Prize media:

“The discoveries of the electron and radioactivity at the end of the nineth century led to different models for the structure of the atom. In 1913, Niels Bohr proposed a theory for the hydrogen atom based on quantum theory that energy is transferred only in certain well defined quantities. Electrons should move around the nucleus but only in prescribed orbits. When jumping from one orbit to another with lower energy, a light quantum is emitted. Bohr's theory could explain why atoms emitted light in fixed wavelengths.”

“Niels Bohr,” Nobel Prize Foundation

Nobel Laureate, Physics Prize, 1922