The Bohr Model of the Atom K. Lee Lerner scholar.harvard.edu/kleelerner kleelerner@alumni.harvard.edu This article is part of a series of essays identifying and explaining theories essential to understanding modern scientific thought. This is a DRAFT COPY of an article that appeared in World of Physics and other STEM references (print and online) books published by Thomson Gale or Cnegage Gale. The content of this article was subsequently revised and published in Scientific Thought: In Context, edited by Brenda Wilmoth Lerner and K. Lee Lerner, and published in two volumes by Thomson Gale (now Cengage Gale) in 2010. The Bohr model of atomic structure was developed by Danish physicist and Nobel laureate Niels Bohr (1885-1962). Published in 1913, Bohr's model improved the classical atomic models of physicists J. J. Thomson and Ernest Rutherford by incorporating quantum theory. While working on his doctoral dissertation at Copenhagen University, Bohr studied physicist Max Planck's quantum theory of radiation. After graduation, Bohr worked in England with Thomson and subsequently with Rutherford. During this time Bohr developed his model of atomic structure. Before Bohr, the classical model of the atom was similar to the Copernican model of the solar system where, just as planets orbit the sun, electrically negative electrons moved in orbits about a relatively massive, positively charged nucleus. The classical model of the atom allowed electrons to orbit at any distance from the nucleus. This predicted that when, for example, a hydrogen atom was heated, it should produce a continuous spectrum of colors as it cooled because its electron, moved away from the nucleus by the heat energy, would gradually give up that energy as it spiraled back closer to the nucleus. Spectroscopic experiments, however, showed that hydrogen atoms produced only certain colors when heated. In addition, physicist James Clark Maxwell's influential