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{{Infobox Scientist
|name              = Robert Sanderson Mulliken
|box_width         =
|image             =Replace_this_image_male.svg 
|image_width       =150px
|caption           = Robert Sanderson Mulliken
|birth_date        = [[June 7]], [[1896]]
|birth_place       = [[Newburyport, Massachusetts]]
|death_date        = [[October 31]], [[1986]]
|death_place       = [[Arlington, Virginia]]
|residence         = 
|citizenship       = 
|nationality       = [[United States|American]]
|ethnicity         = 
|field             = [[physics|physicist]]
|work_institutions = 
|alma_mater        = 
|doctoral_advisor  = 
|doctoral_students = 
|known_for         = [[molecular orbital theory]]
|author_abbrev_bot = 
|author_abbrev_zoo = 
|influences        = 
|influenced        = 
|prizes            = [[Image:Nobel prize medal.svg|20px]][[Nobel Prize for chemistry]],  [[1966]]<br/>[[Priestley Medal]], [[1983]]
|religion          = 
|footnotes         = 
|signature         =
}}
{{EH}}	

'''Robert Sanderson Mulliken''' ([[June 7]], [[1896]] &ndash; [[October 31]], [[1986]]) was an [[United States|American]] [[physics|physicist]] and [[chemistry|chemist]], primarily responsible for the early development of [[molecular orbital theory]], i.e. the elaboration of the [[molecular orbital]] method of computing the structure of [[molecule]]s.  Dr. Mulliken received the [[Nobel Prize]] for chemistry in 1966.  He received the [[Priestley Medal]] in 1983.

==Early years==
Mulliken was born in [[Newburyport, Massachusetts]]. His father, Samuel Parsons Mulliken, was a professor of [[organic chemistry]] at the [[Massachusetts Institute of Technology]]. As a child, Robert Mulliken learned the name and [[botany|botanical]] classification of [[plant]]s and, in general, had an excellent, but selective, memory. For example, he learned [[German language|German]] well enough to skip the course in scientific German in college, but could not remember the name of his high school German teacher. He also made the acquaintance, while still a child, of the physical chemist [[Arthur Amos Noyes]].

Mulliken helped with some of the editorial work when his father wrote his four-volume text on organic compound identification, and thus became an expert on [[Organic nomenclature|organic chemical nomenclature]].

===Education===
In high school in Newburyport, Mulliken took a scientific curriculum. He graduated in 1913 and succeeded in getting a scholarship to MIT that had earlier been won by his father. Like his father, he majored in [[chemistry]]. Already as an undergraduate, he did his first publishable research: on the synthesis of organic chlorides. Because he was unsure of his future direction, he included some [[chemical engineering]] courses in his curriculum and spent a summer touring chemical plants in [[Massachusetts]] and [[Maine]]. He received his [[Bachelor of Science|B. S.]] [[academic degree|degree]] in chemistry from MIT in 1917. 

====Early career====
At this time, the [[United States]] had just entered [[World War I]], and Mulliken took a position at [[American University]] in [[Washington, D.C.]],  making poison gas under [[James B. Conant]]. After nine months, he was drafted into the Army's Chemical Warfare Service, but continued on the same task. His laboratory techniques left much to be desired, and he was out of service for months with burns. Later he got a bad case of influenza, and was still in the hospital at war's end.

After the war, he took a job investigating the effects of zinc oxide and [[carbon]] black on rubber, but quickly decided that this was not the kind of chemistry he wanted to pursue. So in 1919 he entered the [[Doctor of Philosophy|Ph. D.]] program at the [[University of Chicago]].

===Graduate and early postdoctoral education===
He got his doctorate in 1921 based on research into the separation of [[isotope]]s of [[Mercury (element)|mercury]] by [[evaporation]], and continued in his isotope separation by this method. While at [[Chicago]], he took a course under the [[Nobel Prize in Physics|Nobel Prize-winning physicist]] [[Robert A. Millikan]], which exposed him to the [[old quantum theory]]. He also became interested in strange [[molecule]]s after exposure to work by [[Hermann I. Schlesinger]] on [[diborane]].

At Chicago, he had received a grant from the National Research Council (NRC) which had paid for much of his work on isotope separation. The NRC grant was extended in 1923 for two years so he could study isotope effects on band spectra of such diatomic molecules as boron nitride (BN) (comparing molecules with B<sup>10</sup> and B<sup>11</sup>). He went to [[Harvard University]] to learn spectrographic technique from [[Frederick A. Saunders]] and quantum theory from [[E. C. Kemble]]. At the time, he was able to associate with many future luminaries, including [[J. Robert Oppenheimer]], [[John H. Van Vleck]], and [[Harold C. Urey]]. He also met [[John C. Slater]], who had worked with [[Niels Bohr]].

In 1925 and 1927, Mulliken traveled to Europe, working with outstanding spectroscopists and quantum theorists such as [[Erwin Schrödinger]], [[Paul Dirac|Paul A. M. Dirac]], [[Werner Heisenberg]], [[Louis-Victor de Broglie|Louis de Broglie]], [[Max Born]], and [[Walther Bothe]] (all of whom eventually received Nobel Prizes) and [[Friedrich Hund]], who was at the time Born's assistant. They all, as well as [[Wolfgang Pauli]], were developing the new [[quantum mechanics]] that would eventually supersede the old quantum theory. Mulliken was particularly influenced by Hund, who had been working on quantum interpretation of band spectra of diatomic molecules, the same spectra which Mulliken had investigated at Harvard. In 1927 Mulliken worked with Hund and as a result developed his [[molecular orbital]] theory, in which electrons are assigned to states that extend over an entire molecule. In consequence, molecular orbital theory was also referred to as the ''Hund-Mulliken theory.'''

===Beginning of his scientific career===
From 1926 to 1928, he taught in the [[physics]] department at [[New York University]] (NYU). This was his first recognition as a '''physicist'''; though his work had been considered important by '''chemists,''' it clearly was on the borderline between the two sciences and both would claim him from this point on. Then he returned to the University of Chicago as an associate professor of physics, being promoted to full professor in 1931. He would ultimately hold a position jointly in both the physics and chemistry departments. At both NYU and Chicago, he continued to refine his molecular-orbital theory.

Up to this point, the primary way to calculate the [[electronic structure]] of molecules was based on a calculation by [[Walter Heitler]] and [[Fritz London]] on the [[hydrogen]] molecule (H<sub>2</sub>) in 1927. With improvements by [[John C. Slater]] and [[Linus Pauling]], this method assumed that the [[chemical bond|bonds]] in any molecule could be described in a manner similar to the bond in H<sub>2</sub>, and since it corresponded to chemists' ideas of localized bonds between pairs of atoms, this method (called the '''Valence-Bond (VB)''' or '''Heitler-London-Slater-Pauling (HLSP)''' method), was very popular. However, particularly in attempting to calculate the properties of excited states (molecules that have been excited by some source of energy), the VB method does not always work well. Mulliken's molecular-orbital method, building on the quantitative work of [[John Lennard-Jones]], proved to be more flexible and applicable to a vast variety of types of molecules and molecular fragments, and has totally eclipsed Pauling's valence-bond method. As a result of this development, he received the Nobel Prize in Chemistry in 1966.

Mulliken became a member of the [[United States National Academy of Sciences|National Academy of Sciences]] in 1936, the youngest member in the organization's history, at that time.

[[Mulliken population analysis]] is named after him, a method of assigning charges to atoms in a molecule.

==Family==
On December 24, 1929, he married Mary Helen von Noé, daughter of a [[geology]] professor at the University of Chicago. They had two daughters.

==Later years==
In 1934, he derived a new scale for measuring the [[electronegativity]] of elements. This does not entirely correlate with the scale of [[Linus Pauling]], but is generally in close correspondence.

In [[World War II]], from 1942 to 1945, Mulliken directed the Information Office for the University of Chicago's [[Plutonium]] project. Afterward, he developed mathematical formulas to enable the progress of the molecular-orbital theory.

In 1952 he began to apply [[quantum mechanics]] to the analysis of the reaction between [[Gilbert N. Lewis|Lewis]] [[acid]] and [[Base (chemistry)|base]] [[molecule]]s. (See [[Acid-base reaction theories]].) He became Distinguished Professor of Physics and Chemistry in 1961 and continued in his studies of [[molecular structure]] and [[spectroscopy|spectra]], ranging from diatomic molecules to large complex aggregates. He retired in 1985.

He died of congestive heart failure at his daughter's home in [[Arlington, Virginia]] (across the [[Potomac River]] from [[Washington, D.C.]]) His body was returned to [[Chicago]] for burial.

==References==
*{{Citation
|id = [[PMID]]:17745979
|url= http://www.ncbi.nlm.nih.gov/pubmed/17745979
|last=Platt
|first=
|publication-date=1966 Nov 11
|year=[[1966]]
|title=1966 Nobel Laureate in Chemistry: Robert S. Mulliken.
|volume=154
|issue=3750
|periodical=[[Science (journal)|Science]]
|pages=745-747
|doi = 10.1126/science.154.3750.745
}}





{{Nobel Prize in Chemistry Laureates 1951-1975}}

{{BD|1896|1986|Mulliken, Robert Sanderson}}
[[Category:American physicists]]
[[Category:American chemists]]
[[Category:Massachusetts Institute of Technology alumni]]
[[Category:Nobel laureates in Chemistry]]
[[Category:Florida State University faculty]]
[[Category:Guggenheim Fellows]]
[[Category:International Academy of Quantum Molecular Science members]]
[[Category:People from Essex County, Massachusetts]]
[[Category:Physical chemists]]
[[Category:University of Chicago alumni]]
[[Category:Priestley Medal]]

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