Timeline of Chemistry - 20th Century

20th Century

Mikhail Semyonovich Tsvet invents chromatography, an important analytic technique.
Hantaro Nagaoka proposes an early nuclear model of the atom, where electrons orbit a dense massive nucleus.
Fritz Haber and Carl Bosch develop the Haber process for making ammonia from its elements, a milestone in industrial chemistry with deep consequences in agriculture.
Albert Einstein explains Brownian motion in a way that definitively proves atomic theory.
Leo Hendrik Baekeland invents bakelite, one of the first commercially successful plastics.
Robert Millikan measures the charge of individual electrons with unprecedented accuracy through the oil drop experiment, confirming that all electrons have the same charge and mass.
S. P. L. Sørensen invents the pH concept and develops methods for measuring acidity.
Antonius Van den Broek proposes the idea that the elements on the periodic table are more properly organized by positive nuclear charge rather than atomic weight.
The first Solvay Conference is held in Brussels, bringing together most of the most prominent scientists of the day. Conferences in physics and chemistry continue to be held periodically to this day.
Ernest Rutherford, Hans Geiger, and Ernest Marsden perform the gold foil experiment, which proves the nuclear model of the atom, with a small, dense, positive nucleus surrounded by a diffuse electron cloud.
William Henry Bragg and William Lawrence Bragg propose Bragg's law and establish the field of X-ray crystallography, an important tool for elucidating the crystal structure of substances.
Peter Debye develops the concept of molecular dipole to describe asymmetric charge distribution in some molecules.
Niels Bohr introduces concepts of quantum mechanics to atomic structure by proposing what is now known as the Bohr model of the atom, where electrons exist only in strictly defined orbitals.
Henry Moseley, working from Van den Broek's earlier idea, introduces concept of atomic number to fix inadequacies of Mendeleev's periodic table, which had been based on atomic weight.
Frederick Soddy proposes the concept of isotopes, that elements with the same chemical properties may have differing atomic weights.
J. J. Thomson expanding on the work of Wien, shows that charged subatomic particles can be separated by their mass-to-charge ratio, a technique known as mass spectrometry.
Gilbert N. Lewis publishes "The Atom and the Molecule", the foundation of valence bond theory.
Otto Stern and Walther Gerlach establish concept of quantum mechanical spin in subatomic particles.
Gilbert N. Lewis and Merle Randall publish Thermodynamics and the Free Energy of Chemical Substances, first modern treatise on chemical thermodynamics.
Gilbert N. Lewis develops the electron pair theory of acid/base reactions.
Louis de Broglie introduces the wave-model of atomic structure, based on the ideas of wave-particle duality.
Wolfgang Pauli develops the exclusion principle, which states that no two electrons around a single nucleus may have the same quantum state, as described by four quantum numbers.
Erwin Schrödinger proposes the Schrödinger equation, which provides a mathematical basis for the wave model of atomic structure.
Werner Heisenberg develops the uncertainty principle which, among other things, explains the mechanics of electron motion around the nucleus.
Fritz London and Walter Heitler apply quantum mechanics to explain covalent bonding in the hydrogen molecule, which marked the birth of quantum chemistry.
Linus Pauling publishes Pauling's rules, which are key principles for the use of X-ray crystallography to deduce molecular structure.
Erich Hückel proposes Hückel's rule, which explains when a planar ring molecule will have aromatic properties.
Harold Urey discovers deuterium by fractionally distilling liquid hydrogen.
James Chadwick discovers the neutron.
Linus Pauling and Robert Mulliken quantify electronegativity, devising the scales that now bear their names.
Wallace Carothers leads a team of chemists at DuPont who invent nylon, one of the most commercially successful synthetic polymers in history.
Carlo Perrier and Emilio Segrè perform the first confirmed synthesis of technetium-97, the first artificially produced element, filling a gap in the periodic table. Though disputed, the element may have been synthesized as early as 1925 by Walter Noddack and others.
Eugene Houdry develops a method of industrial scale catalytic cracking of petroleum, leading to the development of the first modern oil refinery.
Pyotr Kapitsa, John Allen and Don Misener produce supercooled helium-4, the first zero-viscosity superfluid, a substance that displays quantum mechanical properties on a macroscopic scale.
Otto Hahn discovers the process of nuclear fission in uranium and thorium.
Linus Pauling publishes The Nature of the Chemical Bond, a compilation of a decades worth of work on chemical bonding. It is one of the most important modern chemical texts. It explains hybridization theory, covalent bonding and ionic bonding as explained through electronegativity, and resonance as a means to explain, among other things, the structure of benzene.
Edwin McMillan and Philip H. Abelson identify neptunium, the lightest and first synthesized transuranium element, found in the products of uranium fission. McMillan would found a lab at Berkeley that would be involved in the discovery of many new elements and isotopes.
Glenn T. Seaborg takes over McMillan's work creating new atomic nuclei. Pioneers method of neutron capture and later through other nuclear reactions. Would become the principal or co-discoverer of nine new chemical elements, and dozens of new isotopes of existing elements.
Jacob A. Marinsky, Lawrence E. Glendenin, and Charles D. Coryell perform the first confirmed synthesis of Promethium, filling in the last "gap" in the periodic table.
Felix Bloch and Edward Mills Purcell develop the process of nuclear magnetic resonance, an analytical technique important in elucidating structures of molecules, especially in organic chemistry.
Linus Pauling uses X-ray crystallography to deduce the secondary structure of proteins.
Alan Walsh pioneers the field of atomic absorption spectroscopy, an important quantitative spectroscopy method that allows one to measure specific concentrations of a material in a mixture.
Robert Burns Woodward, Geoffrey Wilkinson, and Ernst Otto Fischer discover the structure of ferrocene, one of the founding discoveries of the field of organometallic chemistry.
James D. Watson and Francis Crick propose the structure of DNA, opening the door to the field of molecular biology.
Jens Skou discovers Na⁺/K⁺-ATPase, the first ion-transporting enzyme.
Max Perutz and John Kendrew use X-ray crystallography to elucidate a protein structure, specifically sperm whale myoglobin.
Neil Bartlett synthesizes xenon hexafluoroplatinate, showing for the first time that the noble gases can form chemical compounds.
George Olah observes carbocations via superacid reactions.
Richard R. Ernst performs experiments that will lead to the development of the technique of Fourier transform NMR. This would greatly increase the sensitivity of the technique, and open the door for magnetic resonance imaging or MRI.
Robert Burns Woodward and Roald Hoffmann propose the Woodward-Hoffmann rules, which use the symmetry of molecular orbitals to explain the stereochemistry of chemical reactions.
Hotosi Nozaki and Ryōji Noyori discovered the first example of asymmetric catalysis (hydrogenation) using a structurally well-defined chiral transition metal complex.
John Pople develops the Gaussian program greatly easing computational chemistry calculations.
Yves Chauvin offered an explanation of the reaction mechanism of olefin metathesis reactions.
Karl Barry Sharpless and group discover a stereoselective oxidation reactions including Sharpless epoxidation, Sharpless asymmetric dihydroxylation, and Sharpless oxyamination.
Harold Kroto, Robert Curl and Richard Smalley discover fullerenes, a class of large carbon molecules superficially resembling the geodesic dome designed by architect R. Buckminster Fuller.
Sumio Iijima uses electron microscopy to discover a type of cylindrical fullerene known as a carbon nanotube, though earlier work had been done in the field as early as 1951. This material is an important component in the field of nanotechnology.
First total synthesis of Taxol by Robert A. Holton and his group.
Eric Cornell and Carl Wieman produce the first Bose–Einstein condensate, a substance that displays quantum mechanical properties on the macroscopic scale.

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