Peter Debye

Dutch American physical chemist

• Born: March 24, 1884; Maastricht, the Netherlands
• Died: November 2, 1966; Ithaca, New York

Dutch American scientist Peter Debye made significant contributions to chemistry, including his pioneering work on electrolytic disassociation, now known as the Debye–Hückel theory. Debye’s research also led to the calculation of the molecular dipole moment. The unit of the dipole has been termed the Debye in his honor. Debye was awarded the 1936 Nobel Prize for his various contributions to molecular chemistry and physics.

Also known as: Petrus Josephus Wilhelmus Debije

Primary field: Chemistry

Specialty: Physical chemistry

Early Life

Peter Debye was born Petrus Josephus Wilhelmus Debije in the Dutch city of Maastricht. He was born into a modest family and his father worked as an ironsmith in a small factory. Debye attended the Hogere Burger School, graduating in 1901 as the top student in the entire province. Debye then entered the Technische Hochschule (Institute of Technology) in Aachen, Germany, just over the Dutch border. As a student, Debye found himself drawn to mathematics and physics and began focusing on scientific pursuits. In 1904, while still a student, Debye was offered a position working as a research assistant to Arnold Sommerfeld, the school’s professor of technical mechanics.

Debye graduated with a degree in engineering in 1905 and continued working with Sommerfeld. In 1906, Sommerfeld accepted a position as chair of theoretical physics at the University of Munich. He asked Debye to accompany him to the university and to apply for a doctorate program. Debye followed Sommerfeld’s recommendation, entering the University of Munich and graduating with his PhD in physics in 1908. Debye remained at the university for his postgraduate studies, which he completed in 1910. Debye’s graduate thesis project focused on the effect of radiation on spherical particles.

In 1911, Debye was offered a position as professor of theoretical physics at Zurich University in Switzerland, succeeding physicist Albert Einstein in the post. Debye transferred to the University of Utrecht in the Netherlands the following year and was awarded another professorship at Göttingen University in 1914. There, he became the director of the theoretical branch of the physics institute. He remained there until 1920.

Life’s Work

Debye’s first major contributions to experimental physics and chemistry came during the year he worked at Zürich University. His first year at the university proved a productive one for Debye. Building on Einstein’s work connecting the specific heat of a solid to the vibrations of its atoms, Debye showed that atomic solids have various frequencies at which they vibrate, rather than just the one frequency that Einstein proposed. He also clarified the specific heat (the measurement of the ability to absorb heat) of solids.

In addition, Debye began studying the dipole moment of molecules, which is a measurement of both the positive and negative electrical charges of a molecule multiplied by the distance between them. Debye was the first to show that molecules had magnetic poles and the first to create a functional system for calculating the extent of this electrical charge. His findings allowed for the creation of molecular structures of materials.

After he accepted a professorship at Göttingen University, in 1914, Debye began conducting research on X-ray scattering, or X-ray diffraction, a method for using X-rays to investigate the atomic and molecular structure of certain materials. Debye’s research built on the techniques invented by Australian physicists William Henry Bragg and William Lawrence Bragg, who were later awarded the Nobel Prize in physics. The system developed by the Braggs only enabled X-ray scattering to be used to determine the structure of relatively large samples of crystal. Debye and his assistant Paul Scherrer devised technology and methodology used to apply X-ray scattering techniques to investigate the properties of powders, now called powder diffraction.

From 1914 to 1916, Debye continued to research various aspects of X-ray scattering measurement, eventually applying the technique to a variety of materials, including liquids. Debye’s research in this area complemented Swedish physicist Ivar Waller’s work; the two researchers are now credited with discovering the Debye–Waller factor, a mathematical system used to describe the scattering of X-rays due to the thermal properties of the materials under study.

Debye accepted a position as professor of physics at the Institute of Technology in Zürich in 1920. Here, Debye researched molecular properties with his assistant and colleague Erich Hückel, a German physicist who had received his doctorate from Göttingen University. Debye and Hückel examined the properties of electrolyte solutions, which are solutions that conduct electricity through the movement of ions. It had been discovered that the observed behavior of electrolyte solutions often departed from the behavior observers expected, given the concentration of ions within the solution. Debye and Hückel derived a theory that disassociated ions in solution are surrounded by ions of a different charge and therefore the movement of any ion is governed by both its concentration and the opposing effect of surrounding ions. From this, Debye and Hückel devised a mathematical formula that described the behavior of ions in electrolyte solutions according to their theory. This became a cornerstone of understanding ionic behavior in electrolyte solutions, now called the Debye-Hückel theory.

In 1927, Debye transferred to the University of Leipzig in Germany, where he took a position as professor of experimental physics. In Leipzig he had the opportunity to continue further research into molecular physics and proposed a theory to explain the Compton effect, which defines the changing wavelength of X-rays colliding with electrons. Debye’s calculations showed how energy from the X-rays is absorbed in scattering electrons, thus resulting in a decrease in energy and increase in wavelength in the associated X-rays.

In 1934, Debye accepted a position at Berlin University, and in 1936 he was awarded the Nobel Prize in Chemistry. In 1939, when Germany invaded Poland, Debye was told that he would have to renounce his Dutch citizenship or resign from the university. Debye refused to take either option, but instead decided to accept a standing offer he had received to lecture in the chemistry department at Cornell University in Ithaca, New York. Debye left Berlin in January 1940, and by July he had been offered a permanent position at Cornell, which he accepted.

Debye remained at Cornell until his retirement in 1952, becoming an American citizen in 1946. As a foreigner, he was kept away from classified military projects during World War II, but did consult on methods to synthesize rubber. Debye continued to engage in research after his official retirement, publishing more than fifty papers on a variety of subjects in molecular and physical chemistry between his retirement and his death in 1966.

Impact

Debye’s research focused on the intersection of chemistry and physics and his work helped to inspire developments in both fields. It is often noted by biographers that Debye’s research into basic physical properties contributed to the growth of quantum physics. He was the first to demonstrate the quantization of electron orbits, which is the way in which the classical model of electron orbits are transitioned to an understanding in keeping with quantum theory. Debye also helped to demonstrate the wave-particle duality and the calculation of the conservation of energy and momentum in his studies on X-ray scattering. His work would become an essential stage in the development of numerous techniques involving molecular engineering and manipulation.

Debye’s research on X-ray diffraction is another cornerstone of his scientific legacy and was one of the primary reasons for his receipt of the 1936 Nobel Prize. The scattering techniques that Debye and his colleagues helped to develop constitute one of the most powerful and useful research tools utilized in physical and molecular chemistry. Debye’s research greatly contributed to the current understanding of molecular bonding and the physical structure of molecules.

Over the course of his career, Debye contributed a number of important discoveries to physics and chemistry. He worked with and trained a large number of physicists and chemists who went on to make significant contributions to the field. In addition to his 1936 Nobel Prize, Debye was awarded the Polymer Physics Prize from the American Physical Society and the National Medal of Science, both in 1965.

Bibliography

Atkins, Peter, Julia de Paulo, and Ron Friedman. Quanta, Matter, and Change: A Molecular Approach to Physical Change. New York: Macmillan, 2008. Print. Contains a discussion of the Debye–Hückel Theory, including information on the development of the theory and its applications.

Courtens, Eric. “Peter Debye: A Life for Science.” Great Solid State Physicists of the 20th Century. Ed. Julio Antonio Gonzalo and Carmen Arago Lopez. Hackensack: World Scientific, 2003. Print. Contains a chapter on the life and research of Peter Debye containing biographical information and a review of Debye’s major contributions to science.

Debye, Peter. The Collected Papers of Peter J. W. Debye. Woodbridge: Oxbow, 1988. Print. A collection of the primary scholarly papers published by Peter Debye during his career.