Niels Bohr

Danish Physicist

1885-1962

Legacy Project 2000

Physical Chemistry 351

Erin Pfeifer

The life of Niels Bohr and the influences he has made in our world are very far reaching. His scientific achievements, especially, have had a profound impact in the scientific community and have revolutionized the way we understand science today. This project is not intended to be complete summary of Niels Bohr, rather I was interested in some of his major trademarks and more important breakthroughs in science. Niels Bohr was an incredible man with an interesting life. I have learned much from this project.

Education

Niels Bohr was born in Copenhagen Denmark on October 7, 1885. His compulsory education was completed in Copenhagen and he also entered the University of Copenhagen in 1903. As a student in 1908, Bohr received his first award of many to come, for an investigation of the surface tension using oscillating fluid jets. This award was offered by the Academy of Sciences in Copenhagen and Bohr received the first place prize. Bohr completed his Master’s in Physics in 1909 and his Doctorate in 1911, with Studies on the electron theory of metals as his thesis. Bohr’s primary research was done in Manchester under Professor Rutherford. Bohr and Rutherford had a good relationship and Rutherford was very receptive to Bohr’s ideas, unlike some of Bohr’s previous research professors.

Research and Bohr’s Atomic Structure

Bohr concentrated the majority of his effort on researching the structure of the atom, and in 1913 he completed his theory of atomic structure. This atomic theory was a combination of Rutherford’s work and ideas of the atom, with Planck’s Quantum Theory. Rutherford’s atomic theory described an atomic model with all the mass concentrated in a nucleus with electrons circling the nucleus in a fixed orbit. This theory was shown incorrect by using Maxwell’s equations, which states since the electrons are moving in a circular motion, they are accelerating. Accelerating electrons means they are emitting radiation and therefore losing energy and would eventually spiral in motion toward the nucleus and collapse. Bohr’s insight was that he declared an electron could orbit the nucleus but only in discrete orbits which didn’t emit radiation. An electron moves to a higher orbit, with a larger radius, by absorbing radiation (a photon) and in contrast will emit a photon of energy when the electron moves to a lower orbit with a smaller radius. Each orbit corresponds to an angular momentum value relating to Planck’s constant (h) divided by 2pi. Insights regarding radiation and atoms were taken from Planck’s Quantum Theory.

Bohr proposed that the outer orbits could accommodate more electrons than the inner orbits. In total, the atomic structure theory that Bohr proposed included an atom which was 1/10,000 the size of the atoms proposed by other scientists. In 1922, Niels Bohr received the Nobel Prize in Physics for his research in the atomic structure.

The figure below illustrates some past and also present atomic models. Thomson, Rutherford, Bohr, and the electron cloud model are present. This figure is taken from the World Book Encyclopedia (1999 edition). The other figure is from Bohr’s lecture for the Nobel Prize. He illustrates the shapes and sizes of the electron orbitals.

Other Theories

*1920-Bohr made descriptions of the periodic table.

*1936-Bohr described the nucleus as a compound structure.

*1939-Uranium isotope fission.

This theory was proposed based on experiments to recognize the

*"Correspondence Principle"-Bohr stated that predictions in quantum

1. Copenhagen interpretation of quantum mechanics
2. Complementarity-Bohr described as how two things can exist as two distinct phenomenea, each equally important and each defined under different circumstances. An example would be how an electron can behave like a particle and a wave. Both are equally important.

Bohr’s Involvement with the Atomic Bomb

As mentioned earlier, Bohr’s understanding and ideas of fission were used to create a chain reaction process that led to the development of the atomic bomb. Bohr used his "Liquid Drop" model to help understand the fission process. During World War II, Bohr and his family fled Denmark in order to escape the Nazi threat towards the Jews. Bohr himself was half Jewish his family and escaped via fishing boat to Sweden. Bohr then traveled to England and participated in discussions regarding the atomic bomb project. Bohr traveled further yet, in 1943, to Los Alamos, New Mexico to work with fellow Danish collegues and other scientists on the Manhattan Project. It is somewhat unclear regarding the exact amount of participation by Bohr, but it is clear that he participated in many discussion concerning the appropriate use and control of the atomic bomb or with any other form of this newly discovered energy source. Bohr was very concerned about the atomic bomb and tended to view the bomb as device that could unify nations, since it could after all, cause catastrophic damage. As part of Bohr’s efforts to promote proper use of the atomic bomb, he wrote a letter 1950 to the United Nations, discussing peaceful policies with nuclear weapons. Bohr also met with Roosevelt and Churchill regarding his attitudes about nuclear energy.

Awards and Positions

*1916-Bohr returned to the University of Copenhagen to teach Physics

*1916-He was appointed Chair of Theoretical Physics at U. or Copenhagen

*Appointed Director of the Niels Bohr Institute

*1922-Won the Nobel Prize in Physics for his atomic structure

*1957-Received the first U.S. Atoms for Peace Award

The Bohr Family

I found in my research that Bohr had a very impressive family, composed of so many intelligent people.

"Anyone who in not dizzy after his first acquaintance with quantum of action has not understood a word".

Acknowledgements