Niels Henrik David Bohr was a Danish physicist born in Copenhagen on October 7th 1885. His father, Christian Bohr, was a college professor at Copenhagen University. Bohr had one younger brother named Harald, who was a mathematician, and a sister named Jennifer (“Niels bohr,” 1992). Bohr married Margrethe Norlund in 1912 and had six children. Unfortunately two were lost, but the remaining four would become very successful like their father. Aage followed in his father’s footsteps as a physicist, receiving the Nobel peace prize in 1975 for his collective model of the nucleus. His other sons would become a chemist, lawyer and physician (“the bohr model”).
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Bohr began his education at Gammelholm Grammar School in 1903, later entering Copenhagen University where he received his masters in physics in 1909. Soon after, in 1911, he received his doctorate. His doctor’s disputation was a theoretical work on the explanation of the properties of the metals with the aid of electron theory. It remains a classic to this day. The same year he received his doctorate, Bohr traveled to Cambridge where he studied under JJ Thompson. Unfortunately, they did not get along, so in 1912 he traveled to Manchester to study under Earnest Rutherford. It was here that he completed a theoretical work on the absorption of alpha rays that was published in Philosophical Magazine in 1913. Working off some of Rutherford’s discoveries about the atomic nucleus, Bohr was able to develop a working model of the atom (“Niels bohr,” 1992).
Perhaps Bohr’s most important work was that with the model of the atom. Bohr’s model, sometimes referred to as the planetary model, was able to provide explanation for concepts that were previously indescribable. Working off Rutherford’s previous work, Bohr was able to successfully explain the spectrum of the hydrogen atom. While Rutherford’s model focused mainly on the nucleus, Bohr paid greater attention to electrons. The previous model of the atom stated an electron was an orbiting planet. The problem in this flawed model was that the electron, moving in a circular path, would be accelerating. Acceleration would create a change in magnetic field, which would in turn carry energy away from the nucleus. The electron would eventually slow and be captured by the nucleus. Bohr’s model expanded upon Rutherford’s and solved many flaws of the previous model (“The Bohr model,”). Bohr discovered that the atom consisted of a small, positive nucleus, with negatively charged electrons traveling around it due to the electrostatic force of coulombs law. (Matthews 2010). Bohr stated that electrons travel only in successively larger orbits. The outer orbits hold more electrons that the inner ones and it’s the outer orbits that determine the atoms chemical properties (“Niels bohr,” 1992).
Although Bohr’s model eliminated many problems of earlier renderings, it was not without its own flaws. Bohr’s model violated the Heisenberg Uncertainty Principle because it states that electrons have both a known orbit and radius. It also made poor predictions about the spectra of larger atoms, did not predict the relative intensities of spectral lines, provided an incorrect value for the ground state orbital angular momentum, did not explain fine structures and hyperfine structures in spectral lines and did not explain the Zeeman effect (“Bohr model of the atom,”). The Zeeman Effect is the splitting of a spectral line by a magnetic field (Foley). Even with these problems, Bohr’s model was still important for laying a foundation for future study. Erwin Schrodinger’s electron could model, made possible by quantum mechanics, and would come to outdate the Bohr model in the 1920’s (“Niels bohr,” 2009).
Along with his structural model of the atom, Bohr was able to explain how atoms emit radiation. He suggested that when an electron jumps from an outer orbit to an inner one, it will emit light. His research found the wavelength of the emitted light is the same as the photon that carries the energy difference between the two orbits. This showed that atoms can only absorb and emit at certain wavelengths. This theory was later expanded into quantum mechanics (“Niels bohr,”).
In 1930 Bohr changed his focus to the constitution of atomic nuclei along with their transmutations and integrations. He found that a liquid droplet would give a very good picture of the nucleus. He developed the liquid droplet theory which helped clarify and provide understanding of the mechanics of nuclear fission and the splitting of the uranium atom. This theory would provide an important basis for future studies in this field by Hahn and Strassmann (“Niels bohr,” 1992).
Bohr was well known for his concept of complementarily. It helped to clarify some of the problems that he found in quantum physics. The theory stated that wave and particle aspects of nature are complementary and cannot both be true at the same time (“Niels bohr,”). In other words something must have either wave or particle like properties, not both. The concept of complementarity stated that “classical concepts such as space-time location and energy-momentum, which in classical physics were always combined into a single picture, cannot be so combined in quantum physics (“Complementarity principle,”).” In certain situations, the use of one certain classical concept will exclude the use of another classical concept. Bohr’s views on the Principle on Complementarity were represented in a number of different essays he wrote from 1933-1926 (“Niels bohr,” 1992).
Bohr was equally famous for his correspondence principle, formulated in 1920(“Niels bohr,”). This principle states that “the behavior of systems described by the theory of quantum mechanics reproduces classical physics in the limit of large quantum numbers (Parker, 1983).” In simpler terms, this principle is the idea that a new theory should be able to reproduce the results of older theories in the domains where those older theories work (“Apply quantum principle,” 1999).
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During the Nazi occupation of Denmark, Bohr being half Jewish, fled the country to escape persecution. He and his family left the country by fishing boat and went to Sweden. Bohr then traveled to England to discuss the invention of the atomic bomb. In 1943 he traveled to Los Alamos New Mexico to work on the Manhattan Project. He, along with other scientists, helped to develop the first atomic bomb. Because it had such a potential to cause catastrophic damage, Bohr viewed the bomb as a device that could unify nations. When the war was over, Bohr returned to Copenhagen and promoted the peaceful use of atomic weapons and energy. “Niels bohr,” 1992).
Bohr gave back to the community by sharing his knowledge. In 1913 he held a lectureship in physics at Copenhagen University and did the same in 1914-1916 at Victoria University in Manchester. He was a professor of theoretical physics at Copenhagen University and from 1920 until his death; he was the head of the Institute of Theoretical Physics. Along with educating future scientists, Bohr was President of the Royal Danish Academy of Sciences and the Danish Cancer Committee, Chairman of the Danish Atomic Energy Commission and a member of the Royal Society and the Royal Institution (“Niels bohr,” 1992).
Throughout his lifetime, Bohr received many different awards for his work in a variety of disciplines. The most prestigious being the Nobel Peace Prize in 1922 for his work on the atomic model. He also received the Hughes Medal in 1921, Matteucci Medal in 1923, Copley Medal in 1938, United States Atoms for Peace Award 1957 and the Sonning Prize 1961(“Niels bohr,”). Bohr had many other honors apart from theses medal and trophies. The institute of physics in Copenhagen was renamed the Niel’s Bohr Institute in his honor. On November 21st 1963 in Demark, the Bohr model semi centennial postage stamp was commemorated featuring Bohr, the hydrogen atom, and his formula for determining the difference in any two hydrogen energy levels. The atomic elements Bohrium and Hafnium were named for him along with asteroid 3948 Bohr.
Towards the end of his life, Bohr began to show an interest in molecular biology. His final work, “Light and Life”, proposed an idea that life might not be reducible to atomic physics. It was unfinished and published after his death (“Niels bohr,”).
Bohr passed away in Copenhagen on November 18th 1962 due to a stroke (“Niels bohr,” 1992). His work had an enormous impact on the scientific world of both his time and today. His extreme strides in developing the model of the atom led to the creation of an accurate model necessary for study in modern physics. His numerous formulas solved many existing problems and would lay the groundwork for future studies. If it were not for Bohr’s passion and dedication to science many modern concepts would not exist today.
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