Bohr`s theory

The Bohr Model is a physical model that depicts the atom as a small positively charged nucleus with electrons in orbit at different levels, similar in structure to the solar system. It is named for the Danish physicist Niels Bohr. Bohr's theory of atomic structure, for which he received the Nobel Prize in physics in 1922, was published in papers between 1913 and 1915. His work drew on Rutherford's nuclear model of the atom, in which the atom is seen as a compact nucleus surrounded by a swarm of much lighter electrons. Bohr's atomic model made use of quantum theory and the Planck constant (the ratio between quantum size and radiation frequency). The model proposes the explanation that an atom emits electromagnetic radiation only when an electron in the atom jumps from one quantum level to another. This model contributed enormously to future developments of theoretical atomic physics.

Developments in the field of quantum mechanics have shown that the Bohr model is not entirely correct. This model has been superceded by the similar wave model. However because of its simplicity, the Bohr model is still commonly used and taught today. Whilst today the Bohr model may look over-simple (and it only works for hydrogen), at the time it was a remarkable feat.

NIELS BOHR:

Bohr was born in Copenhagen on October 7, 1885, the son of a physiology professor, and was educated at the University of Copenhagen, where he earned his doctorate in 1911. That same year he went to Cambridge, England, to study nuclear physics under the British physicist Sir Joseph John Thomson, but he soon moved to Manchester to work with Ernest Rutherford. Bohr's theory of atomic structure, for which he received the Nobel Prize in physics in 1922, was published in papers between 1913 and 1915. In 1916 Bohr returned to the University of Copenhagen as a professor of physics, and in 1920 he was made director of the university's newly formed Institute for Theoretical Physics. He also served as a visiting professor at many universities. In 1939, recognizing the significance of the fission experiments of the German scientists Otto Hahn and Fritz Strassmann, Bohr convinced physicists at a scientific conference in the U.S. of the importance of those experiments. He later demonstrated that uranium-235 is the particular isotope of uranium that undergoes nuclear fission. Bohr then returned to Denmark, where he was forced to remain after the German occupation of the country in 1940. Eventually, however, he was persuaded to escape to Sweden, under peril of his life and that of his family. From Sweden the Bohrs traveled to England and eventually to the United States, where Bohr joined in the effort to develop the first atomic bomb, working at Los Alamos, New Mexico, until the first bomb's detonation in 1945. In 1945 Bohr returned to the University of Copenhagen, where he immediately began working to develop peaceful uses for atomic energy. He organized the first Atoms for Peace Conference in Geneva, held in 1955, and two years later he received the first Atoms for Peace Award. Bohr died in Copenhagen on November 18, 1962.