Physics: 1922

Bohr, Niels (1885-1962), was a noted Danish physicist who developed a theory about the structure of the atom. Bohr's theory, published in 1913, was based on an earlier one proposed by Ernest Rutherford, a New Zealand-born physicist. Rutherford had shown that the atom consisted of a positively charged nucleus, with negatively charged electrons whirling around the nucleus. Bohr proposed that the electrons could travel only in certain successively larger orbits around the nucleus. He thought the outer orbits could hold more electrons than the inner ones. Bohr also suggested that the electrons in the outermost orbit determined the atom's chemical properties.

Bohr, aided by a theory proposed by the German physicist Max Planck, described the way atoms emit radiation. Bohr assumed that when an electron jumps from an outer orbit to an inner one, it emits light. His theory explained the way light is given off by hydrogen, the simplest atom. Later, other scientists expanded Bohr's theory into quantum mechanics. This field of physics explains the structure of more complex atoms, the way they give off light, and other related matters.

Bohr was born on Oct. 7, 1885, in Copenhagen, Denmark. He received a doctor's degree in physics at the University of Copenhagen in 1911. That same year, he traveled to Cambridge, England, to study under the noted British physicist Sir Joseph J. Thomson. Bohr went to Manchester, England, in 1912 to work with Rutherford.

In 1916, Bohr became a professor of physics at the University of Copenhagen. Danish authorities opened the Institute for Theoretical Physics (now called the Niels Bohr Institute) there in 1921, and Bohr became its director. Bohr won the 1922 Nobel Prize in physics chiefly for his work on atomic structure. During the 1930's, Bohr made many contributions to the study of the nucleus of the atom and to an understanding of quantum mechanics.

In 1943, during World War II, Bohr fled from Copenhagen to escape the Nazis. He traveled to Los Alamos, New Mexico, where he advised scientists working on the first atomic bomb. He returned to Copenhagen after the war ended in 1945. Bohr later promoted peaceful uses of nuclear energy. He died on Nov. 18, 1962.

Contributor: Roger H. Stuewer, Ph.D., Professor of the History of Science and Technology, University of Minnesota.