Robert S. Mulliken was a pioneering American physical chemist born on June 7, 1896, in Newburyport, Massachusetts, to Samuel Parsons Mulliken, a Professor of Organic Chemistry. He earned his undergraduate degree from the Massachusetts Institute of Technology and completed his Ph.D. in physics at the University of Chicago in 1921 under the guidance of Robert A. Millikan. Mulliken began his academic career at New York University from 1926 to 1928 before joining the University of Chicago faculty where he remained for over five decades until 1985. He later served as Distinguished Professor of Physics and Chemistry at Florida State University until his retirement. His distinguished career spanned the golden age of quantum chemistry development, establishing him as one of the field's foundational figures.
Mulliken's most significant contribution was the development of molecular orbital theory, which revolutionized the understanding of chemical bonding and molecular structure. Departing from the concept of static atomic orbitals, he proposed that when molecules form, the atoms' original electron configurations transform into an overall molecular configuration with electrons occupying molecular orbitals that extend across the entire molecule. His theoretical framework systematized the electron states of molecules and provided the quantum-mechanical foundation for understanding chemical bonds. This groundbreaking work earned him the 1966 Nobel Prize in Chemistry, awarded specifically for his fundamental work concerning chemical bonds and the electronic structure of molecules by the molecular orbital method. His contributions were so profound that he became widely known throughout the scientific community as Mr. Molecule.
Beyond his theoretical contributions, Mulliken made significant impacts during World War II as Director of the Information Division for the University of Chicago's Plutonium Project, part of the Manhattan Project, where he helped draft the first Prospectus on Nucleonics outlining peaceful applications of atomic energy. He was instrumental in establishing the Division of Chemical Physics in 1951 and served as its inaugural chairman, helping to shape the field's institutional structure. Mulliken maintained an active research group that continued to advance molecular science through experimental spectroscopy and theoretical developments well into his later years. His legacy endures through the widespread adoption of molecular orbital theory as a cornerstone of modern quantum chemistry education and research. The profound influence of his work continues to shape how scientists understand and predict molecular behavior across chemistry, physics, and materials science.
