Editing Robert S. Mulliken (section)

==Early years==
Robert Mulliken was born in [[Newburyport, Massachusetts]] on June 7 1896. 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 plants 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 followed a scientific curriculum. He graduated in 1913 and succeeded in getting a scholarship to MIT which had earlier been won by his father. Like his father, he majored in [[chemistry]]. Already as an undergraduate, he conducted 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 contracted a bad case of influenza, and was still hospitalized 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. Hence, in 1919 he entered the Ph.D. program at the [[University of Chicago]].

===Graduate and early postdoctoral education===
Mulliken 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 molecules after exposure to work by [[Hermann I. Schlesinger]] on [[diborane]].

[[File:Hund,Friedrich 1929 Chicago.jpg|thumb|300px|Robert Mulliken, Chicago 1929 (third from right)]]
At Chicago, he had received a grant from the [[United States National Research Council|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 [[J. Robert Oppenheimer]] and many future Nobel laureates, including [[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.'''

===Early 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 ultimately held 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 the conception of hybridized atomic orbitals by [[John C. Slater]] and [[Linus Pauling]], which rationalized observed molecular geometries, the method was based on the premise that the [[chemical bond|bonds]] in any molecule could be described in a manner similar to the bond in H<sub>2</sub>, namely, as overlapping atomic orbitals centered on the atoms involved.  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. In attempting to calculate the properties of excited states (molecules that have been excited by an energy source), the VB method does not always work well. With its description of the electron wave functions in molecules as delocalized molecular orbitals that possess the same symmetry as the molecule, Hund and Mulliken's molecular-orbital method, including contributions by [[John Lennard-Jones]], proved to be more flexible and applicable to a vast variety of types of molecules and molecular fragments, and has eclipsed the 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 the time.<ref>{{Cite web |title=Robert S. Mulliken |url=http://www.nasonline.org/member-directory/deceased-members/52287.html |access-date=2023-05-03 |website=www.nasonline.org}}</ref> He was elected to the [[American Philosophical Society]] in 1940 and the [[American Academy of Arts and Sciences]] in 1965.<ref>{{Cite web |title=APS Member History |url=https://search.amphilsoc.org/memhist/search?creator=Robert+S.+Mulliken&title=&subject=&subdiv=&mem=&year=&year-max=&dead=&keyword=&smode=advanced |access-date=2023-05-03 |website=search.amphilsoc.org}}</ref><ref>{{Cite web |title=Robert Sanderson Mulliken |url=https://www.amacad.org/person/robert-sanderson-mulliken |access-date=2023-05-03 |website=American Academy of Arts & Sciences |date=9 February 2023 |language=en}}</ref> He was elected a [[List of Fellows of the Royal Society elected in 1967|Foreign Member of the Royal Society (ForMemRs) in 1967]].<ref name="frs"/>

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