1. Overview
Friedrich Hermann Hund (Friedrich Hermann HundFriedrich Hermann HundGerman; February 4, 1896 - March 31, 1997) was a prominent German physicist from Karlsruhe. He is widely recognized for his fundamental contributions to atomic physics and molecular physics. His most significant scientific achievements include the formulation of Hund's rules for predicting electron configurations, the development of Hund's cases which describe particular regimes in diatomic molecular angular momentum coupling, and his collaborative work on molecular orbital theory (often known as the Hund-Mulliken theory). Hund also made a pioneering identification of the quantum tunneling effect. His work played a pivotal role in advancing quantum theory and shaped modern scientific understanding in physics and chemistry.
2. Life
Friedrich Hermann Hund's life was marked by extensive academic pursuits and significant contributions to theoretical physics. His journey began with his education in various scientific fields, leading to a distinguished career across several German universities and international research institutions.
2.1. Early Life and Education
Friedrich Hund pursued his higher education at the University of Marburg and the University of Göttingen. During his studies, he specialized in a comprehensive curriculum that included mathematics, physics, and geography.
2.2. Academic Career
Hund commenced his academic career in 1925, serving as a private lecturer for theoretical physics at the University of Göttingen. His career then progressed through a series of significant professorial appointments at various prestigious institutions. In 1927, he became a professor of theoretical physics at the University of Rostock. This was followed by a professorship in mathematical physics at Leipzig University in 1929. After a period, he moved to the University of Jena in 1946, where he was a professor of theoretical physics, and subsequently to the Goethe University Frankfurt in 1951, also as a professor of theoretical physics. He returned to the University of Göttingen in 1957, resuming his role as a professor of theoretical physics.
Beyond his university appointments in Germany, Hund also undertook important research stays abroad. In 1926, he conducted research in Copenhagen alongside the renowned physicist Niels Bohr. He also served as a visiting lecturer on the atom at Harvard University in 1928. Throughout his prolific career, Hund authored more than 250 academic papers and essays, making substantial contributions to quantum theory, particularly concerning the structure of atoms and the analysis of molecular spectra. He collaborated with many leading physicists of his time, including Erwin Schrödinger, Paul Dirac, Werner Heisenberg, Max Born, and Walther Bothe. During his time as Born's assistant, Hund focused on the quantum interpretation of the band spectra of diatomic molecules.
2.3. Personal Life
On March 17, 1931, Friedrich Hund married Ingeborg Seynsche (1905-1994), a mathematician, in Barmen. The couple had six children. Their children included Gerhard Hund (1932-2024), who became both a chess player and a mathematician; Dietrich (1933-1939); Irmgard (born 1934); Martin (1937-2018); Andreas (born 1940); and Erwin (1941-2022). His granddaughters, Barbara Hund (born 1959) and Isabel Hund (born 1962), both achieved recognition as chess players. Friedrich Hund passed away on March 31, 1997, at the age of 101, and is interred in the Munich Waldfriedhof.
3. Major Scientific Contributions
Friedrich Hund's scientific work laid foundational principles that continue to be central to quantum mechanics, atomic physics, and molecular chemistry. His most impactful contributions include developing rules for electron configurations, defining molecular coupling cases, pioneering molecular orbital theory, and identifying the quantum tunneling effect.
3.1. Hund's Rules and Cases
Hund is widely recognized for Hund's rules, which are empirical rules used to predict the electron configuration of atoms in their ground state. The most prominent among these is Hund's rule of maximum multiplicity (often referred to simply as Hund's Rule in chemistry). This rule states that for a given electron configuration, a state with the maximum possible number of unpaired electrons (and thus maximum total spin angular momentum) has the lowest energy. These unpaired electrons also tend to have parallel spins. Hund's rules are of paramount importance in spectroscopy and quantum chemistry for understanding atomic and molecular properties.
In addition to his rules for atomic electron configurations, Hund also formulated Hund's cases. These describe particular regimes in the angular momentum coupling of diatomic molecules. Hund's cases are crucial for the analysis and interpretation of molecular spectra.
3.2. Molecular Orbital Theory (Hund-Mulliken Theory)
Friedrich Hund played a pivotal role in the development of molecular orbital theory, a fundamental concept in quantum chemistry. His work in this area, carried out in collaboration with the American chemist Robert S. Mulliken, led to the theory often being referred to as the Hund-Mulliken MO theory. This theory provides a framework for understanding molecular structure by describing electrons in molecules as occupying molecular orbitals that extend over the entire molecule, rather than being confined to individual bonds or atoms.
Robert S. Mulliken, who was awarded the Nobel Prize in Chemistry in 1966 for his work on molecular orbital theory, consistently acknowledged the profound influence of Hund's contributions on his own research. Mulliken notably expressed that he would have gladly shared the Nobel Prize with Hund due to the significance of Hund's foundational work. The Hund-Mulliken theory, while sometimes challenging to visualize directly, is remarkably effective in predicting molecular properties and has been instrumental in the advancement of theoretical chemistry, often requiring complex calculations that necessitate the use of computers.
3.3. Quantum Tunneling
In 1926, Friedrich Hund was the first to identify and theoretically describe the phenomenon known as quantum tunneling. This effect, where a quantum particle can pass through a potential energy barrier even if it does not have enough kinetic energy to surmount it, was a groundbreaking discovery. Hund's initial work on quantum mechanical barrier penetration laid crucial groundwork for the understanding of various quantum processes and had a significant influence on the development of the broader field of quantum mechanics.
4. Publications
Friedrich Hund was a prolific author, publishing numerous academic papers and several influential books throughout his career. His publications cover a wide range of topics within theoretical physics, particularly focusing on quantum theory, atomic and molecular structure, and the history of physical concepts.
- Versuch einer Deutung der großen Durchlässigkeit einiger Edelgase für sehr langsame Elektronen, Dissertation, University of Göttingen 1923
- Linienspektren und periodisches System der Elemente, Habilitation Thesis, University of Göttingen, Springer 1927
- Allgemeine Quantenmechanik des Atom- und Molekelbaues, in Handbuch der Physik, Band 24/1, 2nd edn., pp. 561-694 (1933)
- Materie als Feld, Berlin, Springer 1954
- Einführung in die Theoretische Physik, 5 vols. 1944-51, Meyers Kleine Handbücher, Leipzig, Bibliographisches Institut, 1945, 1950/51 (vol. 1: Mechanik, vol. 2: Theorie der Elektrizität und des Magnetismus, vol. 3: Optik, vol. 4: Theorie der Wärme, vol. 5: Atom- und Quantentheorie)
- Theoretische Physik, 3 vols., Stuttgart Teubner, first 1956-57, vol. 1: Mechanik, 5th edn. 1962, vol. 2: Theorie der Elektrizität und des Lichts, Relativitätstheorie, 4th edn. 1963, vol. 3: Wärmelehre und Quantentheorie, 3rd edn. 1966
- Theorie des Aufbaues der Materie, Stuttgart, Teubner 1961
- Grundbegriffe der Physik, Mannheim, Bibliographisches Institut 1969, 2nd edn. 1979
- Geschichte der Quantentheorie, 1967, 2nd edn., Mannheim, Bibliographisches Institut 1975, 3rd edn. 1984; English translation 1974
- Quantenmechanik der Atome, in Handbuch der Physik/Encyclopedia of Physics, Band XXXVI, Berlin, Springer 1956
- Die Geschichte der Göttinger Physik, Vandenhoeck und Ruprecht 1987 (Göttinger Universitätsreden)
- Geschichte der physikalischen Begriffe, 1968, 2nd edn. (2 vols.), Mannheim, Bibliographisches Institut 1978 (vol. 1: Die Entstehung des mechanischen Naturbildes, vol. 2: Die Wege zum heutigen Naturbild), Spektrum Verlag 1996
- Göttingen, Kopenhagen, Leipzig im Rückblick, in Fritz Bopp (ed.) Werner Heisenberg und die Physik unserer Zeit, Braunschweig 1961
- A comprehensive list of his writings, [http://teleschach.de/archiv/schriften_f_hund.htm Verzeichnis der Schriften Friedrich Hund (1896-1997)], contains approximately 300 entries and is available online.
5. Awards and Honours
Friedrich Hund received numerous accolades throughout his distinguished career, acknowledging his profound impact on the field of physics. These honors include prestigious medals, memberships in esteemed academic societies, and posthumous recognitions.
He was awarded the Max Planck Medal in 1943, a highly esteemed award for outstanding achievements in theoretical physics. In 1971, he received the Cotenius Medal, and in 1974, he was honored with the Otto Hahn Prize in physics and chemistry. Hund was also an esteemed member of the International Academy of Quantum Molecular Science, an organization dedicated to promoting quantum molecular science.
Beyond these formal awards, Hund received several posthumous tributes. He was made an honorary citizen of Jena, and a street in the city was named in his honor. In June 2004, a section of a new building for the Physics Department at the University of Göttingen was given the address Friedrich-Hund-Platz 1. Furthermore, the Institute for Theoretical Physics at the University of Göttingen also bears his name.
6. Legacy and Impact
Friedrich Hund's extensive body of work left an indelible mark on the fields of physics and chemistry, fundamentally shaping the understanding of atomic and molecular structures and advancing quantum theory. His contributions provided crucial frameworks that remain cornerstones of modern scientific inquiry.
His 100th birthday was commemorated by the publication of the book Friedrich Hund: Geschichte der physikalischen Begriffe (History of Physical Concepts) in 1996, which reflects his significant contributions to the conceptual development of physics. Werner Kutzelnigg also penned a comprehensive review highlighting Hund's specific and profound impact on chemistry. Hund's deep interest in the history of science was further explored in an interview conducted by Klaus Hentschel and Renate Tobies. His pivotal contributions to quantum theory, particularly in elucidating the structure of atoms and molecular spectra, significantly propelled academic development and refined the contemporary scientific understanding of matter.
