Niels Henrik David Bohr was born in Copenhagen, Denmark on October 7, 1885 to Christian Bohr, a professor of physiology at Copenhagen University, and Ellen Bohr, also known as Adler. Niels was the middle of three children, his older sister Jenny was born in 1883, and his younger brother Harald would eventually become a professor of mathematics. Their father, Christian, was a well-known physiologist and was largely responsible for awakening an interest in physics and math in his children.

Harald Bohr

In October 1891, Niels entered the Grammelholms School. He did well in school but was not outstanding, usually coming third or fourth in a class of about 20 students. The subject he excelled at was, surprisingly, physical education. He was an excellent soccer player, but not as good as his brother Harald who won a silver medal playing soccer for Denmark.

In 1903, Bohr entered Copenhagen University, and graduated in 1911 with his doctorate. He went on to study at Cambridge under the eminent physicist J.J. Thompson, and later to Manchester University to study with Ernest Rutherford. Rutherford was much more receptive to Bohr's new ideas and the two of them formed a very close personal and working relationship that resulted in Bohr producing his theory of the hydrogen atom in 1913 at the age of 27.

Bohr worked on the theoretical implications of the nuclear model of the atom that had been recently proposed by Rutherford. Bohr was among the first to see the importance of atomic number, which indicates the position of an element on the periodic table and is equal to the number of protons in the nuclei of atoms. Bohr also recognized that the various physical and chemical properties of the elements depend upon the electrons moving around the nuclei of atoms.

Bohr revolutionized the view of the atom. Rutherford’s model of the atom had pictured a small dense nucleus with electrons swirling around it randomly like planets in the solar system. While it was a crucial step towards understanding atomic structure, Rutherford’s model was both mechanically and electromagnetically unstable. Bohr stabilized Rutherford’s model by introducing the new and not yet clarified ideas of quantum theory being developed by Max Planck, Albert Einstein, and other physicists. Departing radically from classical physics, Bohr postulated that the electrons in an atom could exist only in a discrete set of orbitals or electron shells, each characterized by a definite value of its energy. This description of atomic structure is known as the Bohr atomic model and is discussed in detail in our Atomic Theory II module.  In recognition of this work, Bohr was awarded the Nobel Prize in physics in 1922.

Niels Bohr and Margrethe Nørlund

In 1912 Bohr married Margrethe Nørlund and had six sons. One of Bohrs sons, Aage, followed his father into physics and also won a Nobel Prize in 1975. Niels returned to Denmark as a professor at the University of Copenhagen, and in 1921 the University established the Institute for Theoretical Physics for him. Bohr served as director of the Institute for the rest of his life. Bohr's personal warmth, good humor ("Never express yourself more clearly than you can think," he once said), and hospitality combined with world events to make Copenhagen a refuge for many of the century's greatest physicists.

In the 1930’s, as Adolph Hitler rose to power in Germany, Bohr became deeply concerned for his colleagues, and offered a place for many escaping Jewish scientists to live and work. In 1939 Bohr visited the United States with news that German scientists were working to split the atom. This information prompted the United States to launch the Manhattan Project and develop the atomic bomb.

Shortly after Bohr's return home, the German army occupied Denmark. Three years later, Bohr's family fled to Sweden in a fishing boat. Bohr and his son Aage soon left Sweden, traveling in an empty bomb rack of a British military plane. Bohr and Aage then traveled to the United States, where both joined the government's team of physicists working on the atomic bomb at Los Alamos National Laboratory. Bohr had reservations about the moral consequences of the bomb and angered Winston Churchill by promoting postwar arms control. In his later years, Bohr devoted his work to the peaceful application of atomic physics. On June 9, 1950, Bohr sent a letter to the United Nations advocating full openness between nations over atomic technology and went on to organize the Atoms for Peace Conference in Geneva in 1955.

On November 18, 1962, Niels Bohr died from a heart attack in his home in Copenhagen.

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