Niels Bohr (7 October 1885 – 18 November 1962) was a Danish
physicist who made foundational contributions to understanding
atomic structure and
quantum theory. He advanced the theory of
electrons travelling in
orbits around the atom's nucleus, with the chemical properties of each
element being largely determined by the number of electrons in the outer orbits of its atoms. He introduced the idea that an electron could drop from a higher-energy orbit to a lower one, in the process emitting a
quantum of discrete energy. For his work, he received the
Nobel Prize in Physics in 1922.
Photograph credit: Bain News Service; restored by Bammesk