Most of Peter Debye's professional work involved the application of physical laws to the structure and behavior of molecules. In the 1910s, for example, he determined the dipole moments of many molecules, obtaining results that allowed him to calculate the polarity of such molecules. In recognition of this work, the unit of dipole moment, the debye, was named in his honor. Debye was also awarded the 1936 Nobel Prize in chemistry for this research, although he is perhaps best known for his contribution to the theory of electrolytic dissociation, the Debye-Hückel theory, announced in 1923. Driven out of Germany and the Netherlands during World War II, Debye immigrated to the United States and became professor of chemistry at Cornell University.
Debye was born Petrus Josephus Wilhelmus Debije on March 28, 1884, in Maastrict, the Netherlands. He is better known by the Anglicized form of his name, Peter Joseph William (or Wilhelm) Debye. His father, Joannes Wilhelmus Debije, was a foreman at a metalware manufacturer, while his mother was the former Maria Anna Barbara Ruemkens, a theater cashier prior to her marriage. The Debije's had one other child, a daughter four years younger than Peter.
Debye attended the Hoogere Burger School in Maastricht from 1896 to 1901. He then enrolled at the Technische Hochschule in Aachen, thirty kilometers from his home across the Dutch-German border. The cost of an advanced education placed a severe strain on the modest budget of the Debije family. But, as Mansel Davies writes in the Biographical Memoirs of Fellows of the Royal Society, Peter's father vowed that he "would work night and day" to keep his son in school. As a result, Debye eventually completed his studies at Aachen and received his degree in electrical engineering in 1905.
By a stroke of good fortune, one of Debye's teachers at Aachen had been the great German physicist Arnold Sommerfeld. When Sommerfeld was called to the chair of theoretical physics at the University of Münich in 1906, he asked Debye to join him as an assistant. Debye remained at Münich for five years, earning his doctorate in physics in 1908. The subject of his thesis was the effect of radiation on spherical particles with a variety of refractive properties. After earning his degree, Debye continued his research at Münich, serving as lecturer in physics during his last year there.
In 1911, Debye was offered the prestigious chair of theoretical physics at the University of Zürich, a post most recently held by Albert Einstein. Debye remained only a year at Zürich, but it appears to have been an important one. During this time he seems to have made his first serious attack on the question of the physical properties of molecules.
By the early 1900s, a fair amount of information was known about the chemical properties of molecules , but relatively little was known about their physical structure and behavior. Debye chose to deal with one aspect of this topic, the dipole moment of molecules, during his year at Zürich. The dipole moment of a molecule is its tendency to rotate in an external magnetic field, a property that is a function of the distribution of electric charge in (the polarity of) the molecule.
Hoping to do more experimental work than was expected at Zürich, Debye moved to the University of Utrecht in 1912, but stayed in this post only two years. He completed some exploratory research on the dipole of molecules there, but published relatively little on the subject. It was not until nearly a decade later that this research would be brought to fruition, with spectacular success.
In the meanwhile, Debye moved on again, this time to the University of Göttingen in 1914 as professor of theoretical and experimental physics. During his stay at Utrecht, Debye had married Matilde Alberer on April 10, 1913. Matilde was one of three daughters at the boarding house where Debye lived. The Debyes eventually had two children, Peter Paul Ruprecht and Mathilde Maria Gabiele. The younger Peter Debye became a physicist and collaborated with his father on a number of occasions.
Debye's most important work at Göttingen involved X-ray diffraction studies. The use of X rays to determine the structure of materials had been developed only a few years earlier by Max Laue and by William Henry Bragg and William Lawrence Bragg. The most serious problem with the Laue-Bragg discoveries was that they required the preparation of relatively large crystals. Debye, working with a colleague named Paul Scherrer , found that X-ray diffraction could also be used with powders. They developed this technique and eventually reported on the structure of a number of materials examined by this method.
In 1920, Debye returned to the University of Zürich where he served as professor of experimental physics and director of the physics laboratory at the Federal Institute of Technology. It was during his stay at Zürich that Debye developed the concept for which he is probably best known, the Debye-Hückel theory of electrolytic dissociation . Pioneering work on the behavior of electrolytes , substances that conduct electricity through the movement of ions, had been conducted by the Swedish chemist Svante Arrhenius in the late 1880s. Arrhenius had argued that molecules break up spontaneously in solution, with the liberated ions becoming electrolytic agents.
Debye took a different approach to the problem by way of redefining the mathematical application to physicochemical data, instead of to each possible configuration of ions. Electrolytes must dissociate almost completely in solution, he proposed, because they are already completely ionic in the solid state. The reason they do not behave that way in solution, he said, is that each ion has become surrounded by other ions of opposite charge. The movement of ions through a solution, then, is disturbed by the dragging effect of the surrounding ions. Working with a colleague, Erich Hückel, Debye generated a mathematical theory that precisely described the behavior of electrolytes in solution.
After his success with solution theory, Debye returned to his research on X-ray diffraction. In 1923, he also developed a theory that mathematically explained the Compton effect --the way the wavelengths of X rays change when they collide with electrons--and provided additional support for the wave-particle theory of electromagnetic radiation. He continued those studies when he moved to the University of Leipzig from 1927 to 1934 and then to the University of Berlin in 1934. The Nobel Prize in chemistry he received in 1936 was given in recognition of his contributions in many fields, including "his contributions to our knowledge of molecular structure through the investigations of dipole moments and on the diffraction of X rays and electrons in gases."
The rise of National Socialism resulted in an increase of political issues in German research, and Debye was soon required to become a German citizen in order to retain his post in Berlin. He chose instead to accept an appointment as professor of chemistry and head of the department at Cornell University in Ithaca, New York, in 1940. He became a U.S. citizen in 1946. Debye officially retired from his Cornell post in 1952, but continued his research in the field of polymer chemistry for another decade.
During this time, Debye was much in demand as a lecturer, both in the United Sates and Europe and remained active in the scientific community until the age of 81. He suffered a heart attack at Kennedy International Airport in April 1966 while awaiting a flight to Europe and then a fatal attack, on November 2, 1966, at his home in Ithaca. During his lifetime, Debye collected a host of honors and awards, including the Rumford Medal of the Royal Society (1930), the Lorentz Medal of the Royal Netherlands Academy of Sciences (1935), the Franklin Medal of the Franklin Institute (1937), the Faraday Medal (1949), as well as the Gibbs Medal (1949), the Kendall Award (1957), the Nichols Medal (1963), and the Priestley Medal (1963) of the American Chemical Society.
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