Robert S. Mulliken
American physical chemist who developed molecular orbital theory.
Robert Sanderson Mulliken (June 7, 1896 – October 31, 1986) was an American physical chemist who pioneered the development of molecular orbital theory, a method for computing molecular structure. He was awarded the Nobel Prize in Chemistry in 1966 and the Priestley Medal in 1983. Born in Newburyport, Massachusetts, his father was an MIT organic chemistry professor. As a child, Mulliken learned plant taxonomy and had a selective memory, once learning German well enough to skip a college course while forgetting his high school German teacher’s name. He also met physical chemist Arthur Amos Noyes as a child. Mulliken helped edit his father’s four-volume text on organic compound identification, becoming an expert in chemical nomenclature. He graduated high school in 1913 and earned a scholarship to MIT, where he majored in chemistry and conducted his first publishable research on organic chlorides. After receiving his B.S. in 1917, he worked on poison gas under James B. Conant, then served in the Army’s Chemical Warfare Service, suffering burns and influenza. In 1919, he entered the University of Chicago, earning a Ph.D. in 1921 for research on mercury isotope separation. At Chicago, he studied under physicist Robert A. Millikan and became interested in diborane. With a National Research Council grant, he studied isotope effects on band spectra of diatomic molecules at Harvard, learning from Frederick A. Saunders and E. C. Kemble. He associated with J. Robert Oppenheimer, John H. Van Vleck, Harold C. Urey, and John C. Slater. In 1925 and 1927, he traveled to Europe, working with Erwin Schrödinger, Paul Dirac, Werner Heisenberg, Louis de Broglie, Max Born, Walther Bothe, and Friedrich Hund. Influenced by Hund, Mulliken developed molecular orbital theory in 1927, also called Hund-Mulliken theory. He taught physics at NYU from 1926 to 1928, then as a Guggenheim Fellow worked at Leipzig with Heisenberg, Edward Teller, and Hund. He returned to the University of Chicago as an associate professor of physics in 1930, becoming full professor in 1931 and holding a joint appointment in chemistry. He continued refining his theory, which contrasted with the valence-bond method developed by Walter Heitler, Fritz London, John Slater, and Linus Pauling.
- field
- Physical chemistry
- nationality
- American
- known_for
- Molecular orbital theory, Mulliken population analysis, electronegativity scale
Lore & Background
As a child, Robert Mulliken learned the names and botanical classifications of plants, demonstrating an excellent but selective memory; for instance, he learned German well enough to skip a college scientific German course but could not recall his high school German teacher’s name. He also assisted with editorial work on his father’s four-volume text on identifying organic compounds, which made him an expert in organic chemical nomenclature. After graduating from high school in Newburyport, he earned a scholarship to MIT, where his father had also studied, and majored in chemistry. As an undergraduate, he conducted his first publishable research on synthesizing organic chlorides. He received his B.S. in 1917, then worked on poison gas production under James B. Conant at American University during World War I. Drafted into the Army’s Chemical Warfare Service, he continued the same task, though his laboratory techniques were poor, leading to months of hospitalization from burns and later influenza. After the war, he briefly investigated the effects of zinc oxide and carbon black on rubber before deciding to pursue a Ph.D. at the University of Chicago, which he earned in 1921 for research on separating mercury isotopes by evaporation.
Reader's Guide
Robert Mulliken's primary contribution was the development of molecular orbital theory, which describes electrons in molecules as delocalized orbitals extending over the entire molecule, in contrast to the valence-bond method that treated bonds as localized between atom pairs. This approach, also called the Hund-Mulliken theory, proved more flexible for calculating excited states and a wide variety of molecular types, eventually eclipsing the valence-bond method. Mulliken also derived a scale for measuring electronegativity based on the average of an atom's ionization enthalpy and electron affinity, and developed Mulliken population analysis for assigning charges to atoms in molecules.
Did You Know?
- Mulliken learned German well enough to skip scientific German in college but could not remember his high school German teacher's name.
- He conducted his first publishable research as an undergraduate at MIT on the synthesis of organic chlorides.
- Mulliken was hospitalized for months during World War I after suffering burns from his laboratory work and later contracting influenza.
Frequently Asked Questions
What is Robert S. Mulliken most famous for?
He developed the foundational ideas of molecular orbital theory, giving chemists a mathematical way to predict molecular structure and bonding. He also introduced the Mulliken population analysis and the Mulliken electronegativity scale, both still referenced in modern chemistry.
What is the Mulliken electronegativity scale?
It is a quantitative measure of an atom's tendency to attract electrons, derived from its ionization energy and electron affinity. Mulliken proposed this approach as a more physically grounded alternative to earlier qualitative scales.
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