Timeline of chemistry

Timeline of chemistry lists important works, discoveries, ideas, inventions, and experiments that significantly changed mankind's understanding of the composition of matter and of the interactions thereof, the modern science known as chemistry. The history of chemistry in its modern form is often considered to begin with the English scientist Robert Boyle, though its roots can be traced back to the earliest recorded history.

Early ideas that later became incorporated into the modern science of chemistry come from two main sources. Natural philosophers such as Aristotle and Democritus used deductive reasoning in an attempt to explain the behavior of the world around them. Alchemists were people who used experimental techniques in an attempt to extend the life or perform material conversions, such as turning base metals into gold.

In the 17th century, a synthesis of the ideas of these two disciplines, that is the "deductive" and the "experimental", leads to the development of a process of thinking known as the scientific method. With the introduction of the scientific method, the modern science of chemistry was born.

Known as "the central science", the study of chemistry is strongly influenced by, and exerts a strong influence on, many other scientific and technological fields. Many events considered central to our modern understanding of chemistry are also considered key discoveries in such fields as physics, biology, astronomy, geology, and materials science to name a few. [cite web | title = Chemistry - The Central Science | work = The Chemistry Hall of Fame | publisher = York University | url = http://www.chem.yorku.ca/hall_of_fame/whychem.htm | accessdate = 2006-09-12]

Pre-17th century

Prior to the acceptance of the scientific method and its application to the field of chemistry, it is somewhat controversial to consider many of the people listed below as "chemists" in the modern sense of the word. However, the ideas of certain great thinkers, either for their prescience, or for their wide and long-term acceptance, bear listing here.;c. 3000 BCE: Egyptians formulate the theory of the Ogdoad, or the “primordial forces”, from which all was formed. These were the elements of chaos, numbered in eight, that existed before the creation of the sun.cite journal | author = J. Gwyn Griffiths | year = 1955 | title = The Orders of Gods in Greece and Egypt (According to Herodotus) | journal = The Journal of Hellenic Studies | volume = 75 | pages = 21–23 | url = http://links.jstor.org/sici?sici=0075-4269%281955%2975%3C21%3ATOOGIG%3E2.0.CO%3B2-R | accessdate = 2007-03-16 | doi = 10.2307/629164 ]

;c. 1900 BCE: Hermes Trismegistus, semi-mythical Egyptian adept king, is thought to have founded of the art of alchemy. [cite web | last = Hoeller | first = Stephan A. | title = On the Trail of the Winged God: Hermes and Hermeticism Throughout the Ages | work = Gnosis: A Journal of Western Inner Traditions (Vol. 40, Summer 1996) | publisher = The Gnosis Archive | year = 1996 | url = http://www.gnosis.org/hermes.htm | accessdate = 2007-03-11]

;c. 1200 BCE: Tapputi-Belatikallim, a perfume-maker and early chemist, was mentioned in a cuneiform tablet in Mesopotamia. [cite web | last = Giese | first = Patsy Ann | title = Women in Science: 5000 Years of Obstacles and Achievements | publisher = SHiPS Resource Center for Sociology, History and Philosophy in Science Teaching | url = http://www1.umn.edu/ships/gender/giese.htm | accessdate = 2007-03-11 ]

;c. 450 BCE: Empedocles asserts that all things are composed of four primal elements: earth, air, fire, and water, whereby two active and opposing forces, love and hate, or affinity and antipathy, act upon these elements, combining and separating them into infinitely varied forms. [cite web | last = Parry | first = Richard | title = Empedocles | work = Stanford Encyclopedia of Philosophy | publisher = Metaphysics Research Lab, CSLI, Stanford University | date = 2005-03-04 | url = http://plato.stanford.edu/entries/empedocles/ | accessdate = 2007-03-11]

;c. 440 BCE: Leucippus and Democritus propose the idea of the atom, an indivisible particle that all matter is made of. This idea is largely rejected by natural philosophers in favor of the Aristotlean view. [cite web | last = Berryman | first = Sylvia | title = Leucippus | work = Stanford Encyclopedia of Philosophy | publisher = Metaphysics Research Lab, CSLI, Stanford University | date = 2004-08-14 | url = http://plato.stanford.edu/entries/leucippus/ | accessdate = 2007-03-11] [cite web | last = Berryman | first = Sylvia | title = Democritus | work = Stanford Encyclopedia of Philosophy | publisher = Metaphysics Research Lab, CSLI, Stanford University | date = 2004-08-15 | url = http://plato.stanford.edu/entries/democritus/ | accessdate = 2007-03-11]

;c. 360 BCE: Plato coins term ‘elements’ ("stoicheia") and in his dialogue Timaeus, which includes a discussion of the composition of inorganic and organic bodies and is a rudimentary treatise on chemistry, assumes that the minute particle of each element had a special geometric shape: tetrahedron (fire), octahedron (air), icosahedron (water), and cube (earth). [cite web | last = Hillar | first = Marian | year = 2004 | url = http://www.socinian.org/aristotles_de_anima.html | title = The Problem of the Soul in Aristotle's De anima | publisher = NASA WMAP | accessdate = 2006-08-10 ]

;c. 350 BCE: Aristotle, expanding on Empedocles, proposes idea of a substance as a combination of "matter" and "form". Describes theory of the Five Elements, fire, water, earth, air, and aether. This theory is largely accepted throughout the western world for over 1000 years. [ cite web | title = HISTORY/CHRONOLOGY OF THE ELEMENTS | url = http://hilltop.bradley.edu/~rbg/el.html | accessdate = 2007-03-12]

; c. 50 BCE: Lucretius publishes "De Rerum Natura", a poetic description of the ideas of Atomism. [cite web | last = Sedley | first = David | title = Lucretius | work = Stanford Encyclopedia of Philosophy | publisher = Metaphysics Research Lab, CSLI, Stanford University | date = 2004-08-04 | url = http://plato.stanford.edu/entries/lucretius/ | accessdate = 2007-03-11]

;c. 300: Zosimos of Panopolis writes some of the oldest known books on alchemy, which he defines as the study of the composition of waters, movement, growth, embodying and disembodying, drawing the spirits from bodies and bonding the spirits within bodies.cite book | last = Strathern | first = Paul | title = Mendeleyev's Dream - The Quest for the Elements | publisher = Berkley Books | year = 2000 | id = ISBN 0-425-18467-6]

;c. 750: Ja'far al-Sadiq criticizes Aristotle's theory of four classical elements.Research Committee of Strasburg University, "Imam Jafar Ibn Muhammad As-Sadiq A.S. The Great Muslim Scientist and Philosopher", translated by Kaukab Ali Mirza, 2000. Willowdale Ont. ISBN 0969949014.]

;c. 815: Abu Musa Jabir ibn Hayyan (aka Geber), an Arab alchemist who is "considered by many to be the father of chemistry", [citation|first=Zygmunt S.|last=Derewenda|year=2007|title=On wine, chirality and crystallography|journal=Acta Crystallographica Section A: Foundations of Crystallography|volume=64|pages=246-258 [247] ] [John Warren (2005). "War and the Cultural Heritage of Iraq: a sadly mismanaged affair", "Third World Quarterly", Volume 26, Issue 4 & 5, p. 815-830.] [Dr. A. Zahoor (1997). [http://www.unhas.ac.id/~rhiza/saintis/haiyan.html JABIR IBN HAIYAN (Geber)] . University of Indonesia.] develops an early experimental method for chemistry, and isolates numerous acids, including hydrochloric acid, nitric acid, citric acid, acetic acid, tartaric acid, and aqua regia. [cite web | title = Father of Chemistry: Jabir Ibn Haiyan | work = Famous Muslism | publisher = Famousmuslims.com | year = 2003 | url = http://www.famousmuslims.com/Jabir%20Ibn%20Haiyan.htm | accessdate = 2007-03-12] He introduced a systematic and experimental approach to scientific research based in the laboratory, in contrast to the ancient Greek and Egyptian alchemists whose works were often allegorical and unintelligble.Kraus, Paul, Jâbir ibn Hayyân, "Contribution à l'histoire des idées scientifiques dans l'Islam. I. Le corpus des écrits jâbiriens. II. Jâbir et la science grecque,". Cairo (1942-1943). Repr. By Fuat Sezgin, (Natural Sciences in Islam. 67-68), Frankfurt. 2002:(cf. cite web|author=Ahmad Y Hassan|title=A Critical Reassessment of the Geber Problem: Part Three|url=http://www.history-science-technology.com/Geber/Geber%203.htm|accessdate=2008-08-09)]

;c. 850: Al-Kindi (aka Alkindus), an Arab chemist, refutes the practice of alchemy and the theory of the transmutation of metals. [Felix Klein-Frank (2001), "Al-Kindi", in Oliver Leaman & Hossein Nasr, "History of Islamic Philosophy", p. 174. London: Routledge.]

;c. 900: Muhammad ibn Zakarīya Rāzi (aka Rhazes), a Persian alchemist, publishes several treatises on chemistry, including some of the earliest descriptions of controlled distillation and extraction methods. He also develops early method for the production of sulfuric acid, [cite web | title = MOHAMMAD IBN ZAKARIYA AL-RAZI | work = Famous Muslism | publisher = Famousmuslims.com | year = 2003 | url = http://www.famousmuslims.com/MOHAMMAD%20IBN%20ZAKARIYA%20AL-RAZI.htm | accessdate = 2007-03-12] and experimentally refutes Aristotle's theory of four classical elements. [G. Stolyarov II (2002), "Rhazes: The Thinking Western Physician", "The Rational Argumentator", Issue VI.]

;c. 1000: Abū al-Rayhān al-Bīrūnī [Michael E. Marmura (1965). "An Introduction to Islamic Cosmological Doctrines. Conceptions of Nature and Methods Used for Its Study by the Ikhwan Al-Safa'an, Al-Biruni, and Ibn Sina" by Seyyed Hossein Nasr", "Speculum" 40 (4), p. 744-746.] and Avicenna, [Robert Briffault (1938). "The Making of Humanity", p. 196-197.] both Persian chemists, refute the practice of alchemy and the theory of the transmutation of metals.

;c. 1220: Robert Grosseteste publishes several Aristotelian commentaries where he lays out an early framework for the scientific method. [ws|"" in the 1913 "Catholic Encyclopedia"]

;c. 1250: Nasīr al-Dīn al-Tūsī (aka Tusi), a Persian chemist, describes an early version of the conservation of mass, noting that a body of matter is able to change but is not able to disappear. [Farid Alakbarov (Summer 2001). [http://azer.com/aiweb/categories/magazine/92_folder/92_articles/92_tusi.html A 13th-Century Darwin? Tusi's Views on Evolution] , "Azerbaijan International" 9 (2).]

;c. 1267: Roger Bacon publishes "Opus Maius", which among other things, proposes an early form of the scientific method, and contains results of his experiments with gunpowder. [ cite web | last = O'Connor | first = J. J. | last2 = Robertson | first2 = E. F. | title = Roger Bacon | work = MacTutor | publisher = School of Mathematics and Statistics University of St Andrews, Scotland | year = 2003 | url = http://www-groups.dcs.st-and.ac.uk/~history/Biographies/Bacon.html | accessdate = 2007-03-12 ]

;c. 1310: Pseudo-Geber, an anonymous Spanish alchemist who wrote under the name of Geber, publishes several books that establish the long-held theory that all metals were composed of various proportions of sulfur and mercury. [cite web | last = Zdravkovski | first = Zoran | last2 = Stojanoski | first2 = Kiro | title = GEBER | publisher = Institute of Chemistry, Skopje, Macedonia | date = 1997-03-09 | url = http://www.pmf.ukim.edu.mk/PMF/Chemistry/chemists/geber.htm | accessdate = 2007-03-12]

;1377: Ibn Khaldun, an Arab chemist, refutes the practice of alchemy and the theory of the transmutation of metals.

;c. 1530: Paracelsus develops the study of iatrochemistry, a subdiscipline of alchemy dedicated to extending the life, thus being the roots of the modern pharmaceutical industry. It is also claimed that he is the first to use the word "chemistry".

;1597: Andreas Libavius publishes "Alchemia", a prototype chemistry textbook. [ cite web | title = FROM LIQUID TO VAPOR AND BACK: ORIGINS | work = Special Collections Department | publisher = University of Delaware Library | url = http://www.lib.udel.edu/ud/spec/exhibits/vapor/origins.htm | accessdate = 2007-03-12 ]

17th and 18th centuries

;1605:Sir Francis Bacon publishes "The Proficience and Advancement of Learning", which contains a description of what would later be known as the scientific method. [ cite web | last = Asarnow | first = Herman | title = Sir Francis Bacon: Empiricism | work = An Image-Oriented Introduction to Backgrounds for English Renaissance Literature | publisher = University of Portland | date = 2005-08-08 | url = http://faculty.up.edu/asarnow/eliz4.htm | accessdate = 2007-02-22 ]

;1605:Michal Sedziwój publishes the alchemical treatise "A New Light of Alchemy" which proposed the existence of the "food of life" within air, much later recognized as oxygen. [ cite web | title = Sedziwój, Michal | work = infopoland: Poland on the Web | publisher = University at Buffalo | url = http://info-poland.buffalo.edu/web/sci_health/science/scientists/sedziwoj/link.shtml | accessdate = 2007-02-22 ]

;1615:Jean Beguin publishes the "Tyrocinium Chymicum", an early chemistry textbook, and in it draws the first-ever chemical equation. [Crosland, M.P. (1959). "The use of diagrams as chemical 'equations' in the lectures of William Cullen and Joseph Black." "Annals of Science, Vol 15, No. 2", Jun.]

;1637:René Descartes publishes "Discours de la méthode", which contains an outline of the scientific method. [ws|"" in the 1913 "Catholic Encyclopedia"]

;1648:Posthumous publication of the book "Ortus medicinae" by Jan Baptist van Helmont, which is cited by some as a major transitional work between alchemy and chemistry, and as an important influence on Robert Boyle. The book contains the results of numerous experiments and establishes an early version of the Law of conservation of mass. [cite web | title = Johann Baptista van Helmont | work = History of Gas Chemistry | publisher = Center for Microscale Gas Chemistry, Creighton University | date = 2005-09-25 | url = http://mattson.creighton.edu/History_Gas_Chemistry/vanHelmont.html | accessdate = 2007-02-23] ;1661:Robert Boyle publishes "The Sceptical Chymist", a treatise on the distinction between chemistry and alchemy. It contains some of the earliest modern ideas of atoms, molecules, and chemical reaction, and marks the beginning of the history of modern chemistry. cite web | title = Robert Boyle | work = Chemical Achievers: The Human Face of Chemical Sciences | publisher = Chemical Heritage Foundation | year = 2005 | url = http://www.chemheritage.org/classroom/chemach/forerunners/boyle.html | accessdate = 2007-02-22 ]

;1662:Robert Boyle proposes Boyle's Law, an experimentally based description of the behavior of gases, specifically the relationship between pressure and volume.

;1754:Joseph Black isolates carbon dioxide, which he called "fixed air". [cite web | last = Cooper | first = Alan | title = Joseph Black | work = History of Glasgow University Chemistry Department | publisher = University of Glasgow Department of Chemistry | year = 1999 | url = http://www.chem.gla.ac.uk/dept/black.htm | accessdate = 2006-02-23 ]

;1758:Joseph Black formulates the concept of latent heat to explain the thermochemistry of phase changes. [cite book | last = Partington | first = J.R. | title = A Short History of Chemistry | publisher = Dover Publications, Inc | year = 1989 | id = ISBN 0-486-65977-1]

;1773-1774: Carl Wilhelm Scheele and Joseph Priestly independently isolate oxygen, called by Priestly "dephlogisticated air" and Scheele "fire air". [cite web | title = Joseph Priestley | work = Chemical Achievers: The Human Face of Chemical Sciences | publisher = Chemical Heritage Foundation | year = 2005 | url = http://www.chemheritage.org/classroom/chemach/forerunners/priestley.html | accessdate = 2007-02-22] [cite web | title = Carl Wilhelm Scheele | work = History of Gas Chemistry | publisher = Center for Microscale Gas Chemistry, Creighton University | date = 2005-09-11 | url = http://mattson.creighton.edu/History_Gas_Chemistry/Scheele.html | accessdate = 2007-02-23]

;1778:Antoine Lavoisier, considered "The father of modern chemistry" ["Lavoisier, Antoine." Encyclopædia Britannica. 2007. Encyclopædia Britannica Online. 24 July 2007 .] , recognizes and names oxygen, and recognizes its importance and role in combustion.cite web | last = Weisstein | first = Eric W. | title = Lavoisier, Antoine (1743-1794) | work = Eric Weisstein's World of Scientific Biography | publisher = Wolfram Research Products | year = 1996 | url = http://scienceworld.wolfram.com/biography/Lavoisier.html | accessdate = 2007-02-23 ]

;1787:Antoine Lavoisier publishes "Méthode de nomenclature chimique", the first modern system of chemical nomenclature.

;1787:Jacques Charles proposes Charles's Law, a corollary of Boyle's Law, describes relationship between temperature and volume of a gas. [cite web | title = Jacques Alexandre César Charles | work = Centennial of Flight | publisher = U.S. Centennial of Flight Commission | year = 2001 | url = http://www.centennialofflight.gov/essay/Dictionary/Charles/DI16.htm | accessdate = 2007-02-23 ]

;1789:Antoine Lavoisier publishes "Traité Élémentaire de Chimie", the first modern chemistry textbook. It is a complete survey of (at that time) modern chemistry, including the first concise definition of the law of conservation of mass, and thus also represents the founding of the discipline of stoichiometry or quantitative chemical analysis. [ cite book | last = Burns | first = Ralph A. | title = Fundamentals of Chemistry | publisher = Prentice Hall | year = 1999 | page = 32 | isbn = 0023173513]

;1797:Joseph Proust proposes the law of definite proportions, which states that elements always combine in small, whole number ratios to form compounds. [ cite web | title = Proust, Joseph Louis (1754-1826) | work = 100 Distinguished Chemists | publisher = European Association for Chemical and Molecular Science | year = 2005 | url = http://www.euchems.org/Distinguished/19thCentury/proustlouis.asp | accessdate = 2007-02-23 ]

;1800:Alessandro Volta devises the first chemical battery, thereby founding the discipline of electrochemistry. [ cite web | title = Inventor Alessandro Volta Biography | work = The Great Idea Finder | publisher = The Great Idea Finder | year = 2005 | url = http://www.ideafinder.com/history/inventors/volta.htm | accessdate = 2007-02-23 ]

19th century

;1803:John Dalton proposes Dalton's Law, which describes relationship between the components in a mixture of gases and the relative pressure each contributes to that of the overall mixture.cite web | title = John Dalton | work = Chemical Achievers: The Human Face of Chemical Sciences | publisher = Chemical Heritage Foundation | year = 2005 | url = http://www.chemheritage.org/classroom/chemach/periodic/dalton.html | accessdate = 2007-02-22]

;1805:Joseph Louis Gay-Lussac discovers that water is composed of two parts hydrogen and one part oxygen by volume. cite web | title = December 6 Births | work = Today in Science History | publisher = Today in Science History | year = 2007 | url = http://www.todayinsci.com/12/12_06.htm | accessdate = 2007-03-12 ]

;1807-1808: Sir Humphry Davy uses electrolysis to isolate numerous elements, including potassium, sodium, calcium, strontium, barium, chlorine and the first discovery of aluminum. [cite web | title = Humphrey Davy | work = Chemical Achievers: The Human Face of Chemical Sciences | publisher = Chemical Heritage Foundation | year = 2005 | url = http://www.chemheritage.org/classroom/chemach/electrochem/davy.html | accessdate = 2007-02-22]

;1808:Joseph Louis Gay-Lussac collects and discovers several chemical and physical properties of air and of other gases, including experimental proofs of Boyle's and Charles's laws, and of relationships between density and composition of gases.

;1808:John Dalton publishes "New System of Chemical Philosophy", which contains first modern scientific description of the atomic theory, and clear description of the law of multiple proportions.

;1808:Jöns Jakob Berzelius publishes "Lärboki Kemien" in which he proposes modern chemical symbols and notation, and of the concept of relative atomic weight. [cite web | title = Jöns Jakob Berzelius | work = Chemical Achievers: The Human Face of Chemical Sciences | publisher = Chemical Heritage Foundation | year = 2005 | url = http://www.chemheritage.org/classroom/chemach/electrochem/berzelius.html | accessdate = 2007-02-22]

;1811:Amedeo Avogadro proposes Avogadro's law, that equal volumes of gases contain equal numbers of particles. [cite web | title = Amedeo Avogadro | work = Chemical Achievers: The Human Face of Chemical Sciences | publisher = Chemical Heritage Foundation | year = 2005 | url = http://www.chemheritage.org/classroom/chemach/periodic/avogadro.html | accessdate = 2007-02-22 ]

;1815:William Prout proposes Prout's hypothesis, that all elements are conglomerations of hydrogen. Later disproven, though the near equivalence of the masses of protons and neutrons can explain the popularity of it. cite web | title = William Prout | url = http://www.cartage.org.lb/en/themes/Biographies/MainBiographies/P/Prout/1.html | accessdate = 2007-03-12]

;1825:Michael Faraday isolates benzene, the first known aromatic hydrocarbon. [ cite web | title = Michael Faraday | work = Famous Physicists and Astronomers | url = http://www.phy.hr/~dpaar/fizicari/xfaraday.html | accessdate = 2007-03-12] ;1825:Friedrich Wöhler and Justus von Liebig perform the first confirmed discovery and explanation of isomers, earlier named by Berzelius. Working with cyanic acid and fulminic acid, they correctly deduce that isomerism was caused by differing arrangements of atoms within a molecular structure. cite web | title = Justus von Liebig and Friedrich Wöhler | work = Chemical Achievers: The Human Face of Chemical Sciences | publisher = Chemical Heritage Foundation | year = 2005 | url = http://www.chemheritage.org/classroom/chemach/chemsynthesis/liebig-wohler.html | accessdate = 2007-02-22 ]

;1827:William Prout classifies biomolecules into their modern groupings: carbohydrates, proteins and lipids.

;1828:Friedrich Wöhler synthesizes urea, thereby establishing that organic compounds could be produced from inorganic starting materials, disproving the theory of vitalism.

;1832:Friedrich Wöhler and Justus von Liebig discover and explain functional groups and radicals in relation to organic chemistry.

;1840:Germain Hess proposes Hess's Law, an early statement of the Law of conservation of energy, which establishes that energy changes in a chemical process depend only on the states of the starting and product materials and not on the specific pathway taken between the two states. [cite web | title = Hess, Germain Henri | url = http://www.cartage.org.lb/en/themes/Biographies/MainBiographies/H/Hess/1.html | accessdate = 2007-03-12 ]

;1847:Hermann Kolbe obtains acetic acid from completely inorganic sources, further disproving vitalism. [ cite web | title = Kolbe, Adolph Wilhelm Hermann | publisher = European Association for Chemical and Molecular Sciences | work = 100 Distinguished European Chemists | year = 2005 | url = http://www.euchems.org/Distinguished/19thCentury/kolbeadolph.asp | accessdate = 2007-03-12]

;1848:Lord Kelvin establishes concept of absolute zero, the temperature at which all molecular motion ceases. [ cite web | last = Weisstein | first = Eric W. | title = Kelvin, Lord William Thomson (1824-1907) | work = Eric Weisstein's World of Scientific Biography | publisher = Wolfram Research Products | year = 1996 | url = http://scienceworld.wolfram.com/biography/Kelvin.html | accessdate = 2007-03-12 ]

;1849:Louis Pasteur discovers that the racemic form of tartaric acid is a mixture of the levorotatory and dextrotatory forms, thus clarifying the nature of optical rotation and advancing the field of stereochemistry. [ cite web | title = History of Chirality | publisher = Stheno Corporation | year = 2006 | url = http://www.sthenocorp.com/history.htm | accessdate = 2007-03-12]

;1852:August Beer proposes Beer's law, which explains the relationship between the composition of a mixture and the amount of light it will absorb. Based partly on earlier work by Pierre Bouguer and Johann Heinrich Lambert, it establishes the analytical technique known as spectrophotometry. [ cite web | title = Lambert-Beer Law | publisher = Sigrist-Photometer AG | date = 2007-03-07 | url = http://www.photometer.com/en/abc/abc_061.htm | accessdate = 2007-03-12 ]

;1855:Benjamin Silliman, Jr. pioneers methods of petroleum cracking, which makes the entire modern petrochemical industry possible. [ cite web | title = Benjamin Silliman, Jr. (1816-1885) | work = Picture History | publisher = Picture History LLC | year = 2003 | url = http://www.picturehistory.com/find/p/17879/mcms.html | accessdate = 2007-03-24]

;1856:William Henry Perkin synthesizes Perkin's mauve, the first synthetic dye. Created as an accidental byproduct of an attempt to create quinine from coal tar. This discovery is the foundation of the dye synthesis industry, one of the earliest successful chemical industries. [cite web | title = William Henry Perkin | work = Chemical Achievers: The Human Face of Chemical Sciences | publisher = Chemical Heritage Foundation | year = 2005 | url = http://www.chemheritage.org/classroom/chemach/chemsynthesis/perkin.html | accessdate = 2007-03-24 ]

;1857:Friedrich August Kekulé von Stradonitz proposes that carbon is tetravalent, or forms exactly four chemical bonds. cite web | title = Archibald Scott Couper and August Kekulé von Stradonitz | work = Chemical Achievers: The Human Face of Chemical Sciences | publisher = Chemical Heritage Foundation | year = 2005 | url = http://www.chemheritage.org/classroom/chemach/chemsynthesis/couper-kekule.html | accessdate = 2007-02-22 ]

;1859-1860: Gustav Kirchhoff and Robert Bunsen lay the foundations of spectroscopy as a means of chemical analysis, which lead them to the discovery of caesium and rubidium. Other workers soon used the same technique to discover indium, thalium, and helium. [ cite web | last = O'Connor | first = J. J. | last2 = Robertson | first2 = E.F. | title = Gustav Robert Kirchhoff | work = MacTutor | publisher = School of Mathematics and Statistics University of St Andrews, Scotland | year = 2002 | url = http://www-groups.dcs.st-and.ac.uk/~history/Biographies/Kirchhoff.html | accessdate = 2007-03-24 ]

;1860:Stanislao Cannizzaro, resurrecting Avogadro's ideas regarding diatomic molecules, compiles a table of atomic weights and presents it at the 1860 Karlsruhe Congress, ending decades of conflicting atomic weights and molecular formulas, and leading to Mendeleev's discovery of the periodic law. [Eric R. Scerri, "The Periodic Table: Its Story and Its Significance", Oxford University Press, 2006.]

;1862:Alexander Parkes exhibits Parkesine, one of the earliest synthetic polymers, at the International Exhibition in London. This discovery formed the foundation of the modern plastics industry. [cite web | title = Alexander Parkes (1813 - 1890) | work = People & Polymers | publisher = Plastics Historical Society | url = http://www.plastiquarian.com/parkes.htm | accessdate = 2007-03-24 ]

;1862:Alexandre-Emile Béguyer de Chancourtois publishes the telluric helix, an early, three-dimensional version of the Periodic Table of the Elements. cite web | title = The Periodic Table | publisher = The Third Millennium Online | url = http://www.3rd1000.com/history/periodic.htm | accessdate = 2007-03-24 ]

;1864:John Newlands proposes the law of octaves, a precursor to the Periodic Law.

;1864:Lothar Meyer develops an early version of the periodic table, with 28 elements organized by valence. cite web | title = Julius Lothar Meyer and Dmitri Ivanovich Mendeleev | work = Chemical Achievers: The Human Face of Chemical Sciences | publisher = Chemical Heritage Foundation | year = 2005 | url = http://www.chemheritage.org/classroom/chemach/periodic/meyer-mendeleev.html| accessdate = 2007-02-22 ]

;1865:Johann Josef Loschmidt determines exact number of molecules in a mole, later named Avogadro's Number. [cite episode |network=NPR |station=KUHF-FM Houston |title=Johann Josef Loschmidt |number=1858 |series=The Engines of Our Ingenuity |serieslink=The Engines of Our Ingenuity |credits=John H. Lienhard |airdate=2003 |transcripturl=http://www.uh.edu/engines/epi1858.htm |accessdate=2007-03-24]

;1865:Friedrich August Kekulé von Stradonitz, based partially on the work of Loschmidt and others, establishes structure of benzene as a six carbon ring with alternating single and double bonds.

;1865:Adolf von Baeyer begins work on indigo dye, a milestone in modern industrial organic chemistry which revolutionizes the dye industry. [ cite web | title = Adolf von Baeyer: The Nobel Prize in Chemistry 1905 | work = Nobel Lectures, Chemistry 1901-1921 | publisher = Elsevier Publishing Company | year = 1966 | url = http://nobelprize.org/nobel_prizes/chemistry/laureates/1905/baeyer-bio.html | accessdate = 2007-02-28] ;1869:Dmitri Mendeleev publishes the first modern periodic table, with the 66 known elements organized by atomic weights. The strength of his table was its ability to accurately predict the properties of as-yet unknown elements.

;1873:Jacobus Henricus van 't Hoff and Joseph Achille Le Bel, working independently, develop a model of chemical bonding that explains the chirality experiments of Pasteur and provides a physical cause for optical activity in chiral compounds. [cite web | title = Jacobus Henricus van't Hoff | work = Chemical Achievers: The Human Face of Chemical Sciences | publisher = Chemical Heritage Foundation | year = 2005 | url = http://www.chemheritage.org/classroom/chemach/chemsynthesis/vanthoff.html | accessdate = 2007-02-22 ]

;1876:Josiah Willard Gibbs publishes "On the Equilibrium of Heterogeneous Substances", a compilation of his work on thermodynamics and physical chemistry which lays out the concept of free energy to explain the physical basis of chemical equilibria. [ cite web | last = O'Connor | first = J. J. | last2 = Robertson | first2 = E.F. | title = Josiah Willard Gibbs | work = MacTutor | publisher = School of Mathematics and Statistics University of St Andrews, Scotland | year = 1997 | url = http://www-groups.dcs.st-and.ac.uk/~history/Biographies/Gibbs.html | accessdate = 2007-03-24 ]

;1877:Ludwig Boltzmann establishes statistical derivations of many important physical and chemical concepts, including entropy, and distributions of molecular velocities in the gas phase. [ cite web | last = Weisstein | first = Eric W. | title = Boltzmann, Ludwig (1844-1906) | work = Eric Weisstein's World of Scientific Biography | publisher = Wolfram Research Products | year = 1996 | url = http://scienceworld.wolfram.com/biography/Boltzmann.html | accessdate = 2007-03-24 ]

;1883:Svante Arrhenius develops ion theory to explain conductivity in electrolytes. [cite web | title = Svante August Arrhenius | work = Chemical Achievers: The Human Face of Chemical Sciences | publisher = Chemical Heritage Foundation | year = 2005 | url = http://www.chemheritage.org/classroom/chemach/electrochem/arrhenius.html | accessdate = 2007-02-22]

;1884:Jacobus Henricus van 't Hoff publishes "Études de Dynamique chimique", a seminal study on chemical kinetics. [ cite web | title = Jacobus H. van 't Hoff: The Nobel Prize in Chemistry 1901 | work = Nobel Lectures, Chemistry 1901-1921 | publisher = Elsevier Publishing Company | year = 1966 | url = http://nobelprize.org/nobel_prizes/chemistry/laureates/1901/hoff-bio.html | accessdate = 2007-02-28]

;1884:Hermann Emil Fischer proposes structure of purine, a key structure in many biomolecules, which he later synthesized in 1898. Also begins work on the chemistry of glucose and related sugars. [ cite web | title = Emil Fischer: The Nobel Prize in Chemistry 1902 | work = Nobel Lectures, Chemistry 1901-1921 | publisher = Elsevier Publishing Company | year = 1966 | url = http://nobelprize.org/nobel_prizes/chemistry/laureates/1902/fischer-bio.html | accessdate = 2007-02-28]

;1884:Henry Louis Le Chatelier develops Le Chatelier's principle, which explains the response of dynamic chemical equilibria to external stresses. [ cite web | title = Henry Louis Le Châtelier | work = World of Scientific Discovery | publisher = Thomson Gale | year = 2005 | url = http://www.bookrags.com/biography/henry-louis-le-chatelier-wsd/ | accessdate = 2007-03-24 ]

;1885:Eugene Goldstein names the cathode ray, later discovered to be composed of electrons, and the canal ray, later discovered to be positive hydrogen ions that had been stripped of their electrons in a cathode ray tube. These would later be named protons. [ cite web | title = History of Chemistry | work = Intensive General Chemistry publisher = Columbia University Department of Chemistry Undergraduate Program | url = http://www.columbia.edu/itc/chemistry/chem-c2507/navbar/chemhist.html | accessdate = 2007-03-24 ]

;1893:Alfred Werner discovers the octahedral structure of cobalt complexes, thus establishing the field of coordination chemistry. [ cite web | title = Alfred Werner: The Nobel Prize in Chemistry 1913 | work = Nobel Lectures, Chemistry 1901-1921 | publisher = Elsevier Publishing Company | year = 1966 | url = http://nobelprize.org/nobel_prizes/chemistry/laureates/1913/werner-bio.html | accessdate = 2007-03-24]

;1894-1898: William Ramsay discovers the noble gases, which fill a large and unexpected gap in the periodic table and led to models of chemical bonding. [cite web | title = William Ramsay: The Nobel Prize in Chemistry 1904 | work = Nobel Lectures, Chemistry 1901-1921 | publisher = Elsevier Publishing Company | year = 1966 | url = http://nobelprize.org/nobel_prizes/chemistry/laureates/1904/ramsay-bio.html | accessdate = 2007-03-20]

;1897:J. J. Thomson discovers the electron using the cathode ray tube. [cite web | title = Joseph John Thomson | work = Chemical Achievers: The Human Face of Chemical Sciences | publisher = Chemical Heritage Foundation | year = 2005 | url = http://www.chemheritage.org/classroom/chemach/atomic/thomson.html | accessdate = 2007-02-22 ]

;1898:Wilhelm Wien demonstrates that canal rays (streams of positive ions) can be deflected by magnetic fields, and that the amount of deflection is proportional to the mass-to-charge ratio. This discovery would lead to the analytical technique known as mass spectrometry. [ cite web | title = Alfred Werner: The Nobel Prize in Physics 1911 | work = Nobel Lectures, Physics 1901-1921 | publisher = Elsevier Publishing Company | year = 1967 | url = http://nobelprize.org/nobel_prizes/physics/laureates/1911/wien-bio.html | accessdate = 2007-03-24]

;1898:Maria Sklodowska-Curie and Pierre Curie isolate radium and polonium from pitchblende. [cite web | title = Marie Sklodowska Curie | work = Chemical Achievers: The Human Face of Chemical Sciences | publisher = Chemical Heritage Foundation | year = 2005 | url = http://www.chemheritage.org/classroom/chemach/atomic/curie.html | accessdate = 2007-02-22 ]

;c. 1900: Ernest Rutherford discovers the source of radioactivity as decaying atoms; coins terms for various types of radiation. cite web | title = Ernest Rutherford: The Nobel Prize in Chemistry 1908 | work = Nobel Lectures, Chemistry 1901-1921 | publisher = Elsevier Publishing Company | year = 1966 | url = http://nobelprize.org/nobel_prizes/chemistry/laureates/1908/rutherford-bio.html | accessdate = 2007-02-28]

20th century

;1903:Mikhail Semyonovich Tsvet invents chromatography, an important analytic technique. [cite web | title = Tsvet, Mikhail (Semyonovich) | work = Compton's Desk Reference | publisher = Encyclopædia Britannica | year = 2007 | url = http://deskreference.britannica.com/ebc/print?tocId=9381267 | accessdate = 2007-03-24 ]

;1904:Hantaro Nagaoka proposes an early nuclear model of the atom, where electrons orbit a dense massive nucleus. cite web | title = Physics Time-Line 1900 to 1949 | publisher = Weburbia.com | url = http://www.weburbia.com/pg/hist3.htm | accessdate = 2007-03-25]

;1905: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. [cite web | title = Fritz Haber | work = Chemical Achievers: The Human Face of Chemical Sciences | publisher = Chemical Heritage Foundation | year = 2005 | url = http://www.chemheritage.org/classroom/chemach/gases/haber.html | accessdate = 2007-02-22 ]

;1905:Albert Einstein explains Brownian motion in a way that definitively proves atomic theory. [ cite web | last = Cassidy | first = David | title = Einstein on Brownian Motion | publisher = The Center for History of Physics | year = 1996 | url = http://www.aip.org/history/einstein/essay-brownian.htm | accessdate = 2007-03-25 ]

;1907:Leo Hendrik Baekeland invents bakelite, one of the first commercially successful plastics. [ cite web | title = Leo Hendrik Baekeland | work = Chemical Achievers: The Human Face of Chemical Sciences | publisher = Chemical Heritage Foundation | year = 2005 | url = http://www.chemheritage.org/classroom/chemach/plastics/baekeland.html | accessdate = 2007-02-22 ]

;1909: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.

;1909: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. [ cite web | title = Robert A. Millikan: The Nobel Prize in Physics 1923 | work = Nobel Lectures, Physics 1922-1941 | publisher = Elsevier Publishing Company | year = 1965 | url = http://nobelprize.org/nobel_prizes/physics/laureates/1923/press.html | accessdate = 2007-07-17]

;1909:S. P. L. Sørensen invents the pH concept and develops methods for measuring acidity. [cite web | title = Søren Sørensen | work = Chemical Achievers: The Human Face of Chemical Sciences | publisher = Chemical Heritage Foundation | year = 2005 | url = http://chemheritage.org/classroom/chemach/electrochem/sorensen.html| accessdate = 2007-02-22 ]

;1911: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. [ cite web |last = Parker | first = David | title = Nuclear Twins: The Discovery of the Proton and Neutron | work = Electron Centennial Page | url = http://www.davidparker.com/janine/twins.html | accessdate = 2007-03-25]

;1911: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 until today. [ cite web | title = Solvay Conference | publisher = Einstein Symposium | year = 2005 | url = http://www.bibalex.org/Einstein2005/About_Solvay.htm | accessdate = 2007-03-28 ]

;1912: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. cite web | title = The Nobel Prize in Physics 1915 | work = Nobelprize.org | publisher = The Nobel Foundation | url = http://nobelprize.org/nobel_prizes/physics/laureates/1915/ | accessdate = 2007-02-28]

;1912:Peter Debye develops the concept of molecular dipole to describe asymmetric charge distribution in some molecules. [ cite web | title = Peter Debye: The Nobel Prize in Chemistry 1936 | work = Nobel Lectures, Chemistry 1922-1941 | publisher = Elsevier Publishing Company | year = 1966 | url = http://nobelprize.org/nobel_prizes/chemistry/laureates/1936/debye-bio.html | accessdate = 2007-02-28] ;1913: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. [ cite web | title = Niels Bohr: The Nobel Prize in Physics 1922 | work = Nobel Lectures, Chemistry 1922-1941 | publisher = Elsevier Publishing Company | year = 1966 | url = http://nobelprize.org/nobel_prizes/physics/laureates/1922/bohr-bio.html | accessdate = 2007-03-25]

;1913: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, [ cite web | last = Weisstein | first = Eric W. | title = Moseley, Henry (1887-1915) | work = Eric Weisstein's World of Scientific Biography | publisher = Wolfram Research Products | year = 1996 | url = http://scienceworld.wolfram.com/biography/Moseley.html | accessdate = 2007-03-25 ]

;1913:Frederick Soddy proposes the concept of isotopes, that elements with the same chemical properties may have differing atomic weights. [ cite web | title = Frederick Soddy The Nobel Prize in Chemistry 1921 | work = Nobel Lectures, Chemistry 1901-1921 | publisher = Elsevier Publishing Company | year = 1966 | url = http://nobelprize.org/nobel_prizes/chemistry/laureates/1921/soddy-bio.html | accessdate = 2007-03-25]

;1913: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. [ cite web | title = Early Mass Spectrometry | work = A History of Mass Spectrometry | publisher = Scripps Center for Mass Spectrometry | year = 2005 | url = http://masspec.scripps.edu/MSHistory/timelines/1897.php | accessdate = 2007-03-26 ]

;1916:Gilbert N. Lewis publishes "The Atom and the Molecule", the foundation of valence bond theory.cite web | title = Gilbert Newton Lewis and Irving Langmuir | work = Chemical Achievers: The Human Face of Chemical Sciences | publisher = Chemical Heritage Foundation | year = 2005 | url = http://www.chemheritage.org/classroom/chemach/chemsynthesis/lewis-langmuir.html | accessdate = 2007-02-22 ]

;1921:Otto Stern and Walther Gerlach establish concept of quantum mechanical spin in subatomic particles. [ cite web | title = Electron Spin | url = http://hyperphysics.phy-astr.gsu.edu/hbase/spin.html | accessdate = 2007-03-26 ]

;1923:Gilbert N. Lewis and Merle Randall publish "Thermodynamics and the Free Energy of Chemical Substances", first modern treatise on chemical thermodynamics. [ cite web | last = LeMaster | first = Nancy | last2 = McGann | first2 = Diane | title = GILBERT NEWTON LEWIS: AMERICAN CHEMIST (1875-1946) | work = Woodrow Wilson Leadership Program in Chemistry | publisher = The Woodrow Wilson National Fellowship Foundation | year = 1992 | url = http://www.woodrow.org/teachers/ci/1992/Lewis.html | accessdate = 2007-03-25]

;1923:Gilbert N. Lewis develops the electron pair theory of acid/base reactions.

;1924:Louis de Broglie introduces the wave-model of atomic structure, based on the ideas of wave-particle duality. [ cite web | title = Louis de Broglie: The Nobel Prize in Physics 1929 | work = Nobel Lectures, Physics 1922-1941 | publisher = Elsevier Publishing Company | year = 1965 | url = http://nobelprize.org/nobel_prizes/physics/laureates/1929/broglie-bio.html | accessdate = 2007-02-28]

;1925: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. [ cite web | title = Wolfgang Pauli: The Nobel Prize in Physics 1945 | work = Nobel Lectures, Physics 1942-1962 | publisher = Elsevier Publishing Company | year = 1964 | url = http://nobelprize.org/nobel_prizes/physics/laureates/1945/pauli-bio.html | accessdate = 2007-02-28]

;1926:Erwin Schrödinger proposes the Schrödinger equation, which provides a mathematical basis for the wave model of atomic structure. [ cite web | title = Erwin Schrödinger: The Nobel Prize in Physics 1933 | work = Nobel Lectures, Physics 1922-1941 | publisher = Elsevier Publishing Company | year = 1965 | url = http://nobelprize.org/nobel_prizes/physics/laureates/1933/schrodinger-bio.html | accessdate = 2007-02-28]

;1927:Werner Heisenberg develops the uncertainty principle which, among other things, explains the mechanics of electron motion around the nucleus. [ cite web | title = Werner Heisenberg: The Nobel Prize in Physics 1932 | work = Nobel Lectures, Physics 1922-1941 | publisher = Elsevier Publishing Company | year = 1965 | url = http://nobelprize.org/nobel_prizes/physics/laureates/1932/heisenberg-bio.html | accessdate = 2007-02-28]

;1927:Fritz London and Walter Heitler apply quantum mechanics to explain covalent bonding in the hydrogen molecule, [Walter Heitler and Fritz London "Wechselwirkung neutraler Atome und homöopolare Bindung nach der Quantenmechanik", "Zeitschrift für Physik" 44 (1927) 455-472.] which marked the birth of quantum chemistry. [Ivor Grattan-Guinness. "Companion Encyclopedia of the History and Philosophy of the Mathematical Sciences". Johns Hopkins University Press, 2003, p. 1266.; Jagdish Mehra, Helmut Rechenberg. "The Historical Development of Quantum Theory". Springer, 2001, p. 540.]

;c. 1930: Linus Pauling proposes Pauling's rules, which are key principles for the use of X-ray crystallography to deduce molecular structure.cite web | title = Linus Pauling: The Nobel Prize in Chemistry 1954 | work = Nobel Lectures, Chemistry 1942-1962 | publisher = Elsevier Publishing Company | year = 1964 | url = http://nobelprize.org/nobel_prizes/chemistry/laureates/1954/pauling-bio.html | accessdate = 2007-02-28] ;1930:Wallace Carothers leads a team of chemists at DuPont who invent nylon, one of the most commercially successful synthetic polymers in history. [cite web | title = Wallace Hume Carothers | work = Chemical Achievers: The Human Face of Chemical Sciences | publisher = Chemical Heritage Foundation | year = 2005 | url = http://www.chemheritage.org/classroom/chemach/plastics/carothers.html | accessdate = 2007-02-22 ]

;1931:Erich Hückel proposes Hückel's rule, which explains when a planar ring molecule will have aromatic properties. [ cite web | last = Rzepa | first = Henry S. | title = The aromaticity of Pericyclic reaction transition states | publisher = Department of Chemistry, Imperial College London | url = http://www.ch.ic.ac.uk/rzepa/pericyclic/ | accessdate = 2007-03-26 ]

;1931:Harold Urey discovers deuterium by fractionally distilling liquid hydrogen. [ cite web | title = Harold C. Urey: The Nobel Prize in Chemistry 1934 | work = Nobel Lectures, Chemistry 1922-1941 | publisher = Elsevier Publishing Company | year = 1965 | url = http://nobelprize.org/nobel_prizes/chemistry/laureates/1934/urey-bio.html | accessdate = 2007-03-26]

;1932:James Chadwick discovers the neutron. [ cite web | title = James Chadwick: The Nobel Prize in Physics 1935 | work = Nobel Lectures, Physics 1922-1941 | publisher = Elsevier Publishing Company | year = 1965 | url = http://nobelprize.org/nobel_prizes/physics/laureates/1935/chadwick-bio.html | accessdate = 2007-02-28]

;1932–1934:Linus Pauling and Robert Mulliken quantify electronegativity, devising the scales that now bear their names. [cite journal |title=Electronegativity from Avogadro to Pauling: II. Late Nineteenth- and Early Twentieth-Century Developments |author=William B. Jensen |journal=Journal of Chemical Education |year=2003 |volume=80 pages=279]

;1937: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. [ cite web | title = Emilio Segrè: The Nobel Prize in Physics 1959 | work = Nobel Lectures, Physics 1942-1962 | publisher = Elsevier Publishing Company | year = 1965 | url = http://nobelprize.org/nobel_prizes/physics/laureates/1959/segre-bio.html | accessdate = 2007-02-28]

;1937:Eugene Houdry develops a method of industrial scale catalytic cracking of petroleum, leading to the development of the first modern oil refinery. [cite web | title = Eugene Houdry | work = Chemical Achievers: The Human Face of Chemical Sciences | publisher = Chemical Heritage Foundation | year = 2005 | url = http://www.chemheritage.org/classroom/chemach/petroleum/houdry.html | accessdate = 2007-02-22 ]

;1937: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. [cite web | title = Pyotr Kapitsa: The Nobel Prize in Physics 1978 | work = Les Prix Nobel, The Nobel Prizes 1991 | publisher = Nobel Foundation | year = 1979 | url = http://nobelprize.org/nobel_prizes/physics/laureates/1978/kapitsa-bio.html | accessdate = 2007-03-26]

;1938:Otto Hahn discovers the process of nuclear fission in uranium and thorium. [cite web | title = Otto Hahn: The Nobel Prize in Chemistry 1944 | work = Nobel Lectures, Chemistry 1942-1962 | publisher = Elsevier Publishing Company | year = 1964 | url = http://nobelprize.org/nobel_prizes/chemistry/laureates/1944/hahn-bio.html | accessdate = 2007-04-07]

;1939: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.

;1940: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 Berkley that would be involved in the discovery of many new elements and isotopes.cite web | title = Glenn Theodore Seaborg | work = Chemical Achievers: The Human Face of Chemical Sciences | publisher = Chemical Heritage Foundation | year = 2005 | url = http://www.chemheritage.org/classroom/chemach/atomic/seaborg.html | accessdate = 2007-02-22 ]

;1941: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.

;1945: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. cite web | title = History of the Elements of the Periodic Table | publisher = AUS-e-TUTE | url = http://www.ausetute.com.au/elemhist.html | accessdate = 2007-03-26 ]

;1945-1946: 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. [ cite web | title = The Nobel Prize in Physics 1952 | work = Nobelprize.org | publisher = The Nobel Foundation | url = http://nobelprize.org/nobel_prizes/physics/laureates/1952/ | accessdate = 2007-02-28]

;1951:Linus Pauling uses X-ray crystallography to deduce the secondary structure of proteins.

;1952: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. [ cite web | last = Hannaford | first = Peter | title = Alan Walsh 1916-1998 | work = AAS Biographical Memoirs | publisher = Australian Academy of Science | url = http://www.science.org.au/academy/memoirs/walsh2.htm | accessdate = 2007-03-26 ]

;1952: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. cite journal | last = Cornforth | first = Lord Todd, John | title = Robert Burns Woodward. 10 April 1917-8 July 1979 | journal = Biographical Memoirs of Fellows of the Royal Society | volume = Vol. 27 | issue = Nov., 1981 | pages = pp. 628–695 | publisher = JSTOR | url = http://links.jstor.org/sici?sici=0080-4606(198111)27%3C628%3ARBW1A1%3E2.0.CO%3B2-W | accessdate = 2007-03-27 | month = Nov | year = 1981 | doi = 10.1098/rsbm.1981.0025 "note: authorization required for web access."]

;1953:James D. Watson and Francis Crick propose the structure of DNA, opening the door to the field of molecular biology. [ cite web | title = The Nobel Prize in Medicine 1962 | work = Nobelprize.org | publisher = The Nobel Foundation | url = http://nobelprize.org/nobel_prizes/medicine/laureates/1962/ | accessdate = 2007-02-28]

;1958:Max Perutz and Sir John Cowdery Kendrew use X-ray crystallography to elucidate a protein structure, specifically Sperm Whale myoglobin. [ cite web | title = The Nobel Prize in Chemistry 1962 | work = Nobelprize.org | publisher = The Nobel Foundation | url = http://nobelprize.org/nobel_prizes/chemistry/laureates/1962/ | accessdate = 2007-02-28]

;1962:Neil Bartlett synthesizes xenon hexafluoroplatinate, showing for the first time that the noble gases can form chemical compounds. [cite web | title = Simple experiment | work = National historic chemical landmarks | publisher = American Chemical Society | url = http://acswebcontent.acs.org/landmarks/bartlett/experiment.html | accessdate = 2007-03-02; Raber, L. Noble Gas Reactivity Research Honored. "Chemical and Engineering News", July 3, 2006, Volume 84, Number 27, p. 43]

;1964: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. [ cite web | title = Richard R. Ernst The Nobel Prize in Chemistry 1991 | work = Les Prix Nobel, The Nobel Prizes 1991 | publisher = Nobel Foundation | year = 1992 | url = http://nobelprize.org/nobel_prizes/chemistry/laureates/1991/ernst-autobio.html | accessdate = 2007-03-27]

;1965: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. ;1985: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. [ cite web | title = The Nobel Prize in Chemistry 1996 | work = Nobelprize.org | publisher = The Nobel Foundation | url = http://nobelprize.org/nobel_prizes/chemistry/laureates/1996/ | accessdate = 2007-02-28]

;1991: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. [ cite web | title = Benjamin Franklin Medal awarded to Dr. Sumio Iijima, Director of the Research Center for Advanced Carbon Materials, AIST | publisher = National Institute of Advanced Industrial Science and Technology | year = 2002 | url = http://www.aist.go.jp/aist_e/topics/20020129/20020129.html | accessdate = 2007-03-27]

;1995:Eric Cornell and Carl Wieman produce the first Bose–Einstein condensate, a substance that displays quantum mechanical properties on the macroscopic scale. [cite web | title = Cornell and Wieman Share 2001 Nobel Prize in Physics | work = NIST News Release | publisher = National Institute of Standards and Technology | year = 2001 | url = http://www.nist.gov/public_affairs/releases/n01-04.htm | accessdate = 2007-03-27]

ee also

*History of chemistry
*Discoveries of the chemical elements
*Nobel Prize in chemistry

References

External links

* [http://www.chemheritage.org/classroom/chemach/index.html Chemical Achievers: The Human Face of the Chemical Sciences]
* [http://scienceworld.wolfram.com/biography/ Eric Weisstein's World of Scientific Biography]
* [http://mattson.creighton.edu/HistoryGasChemistry.html History of Gas Chemistry]
* [http://nobelprize.org/nobel_prizes/lists/all/ list of all Nobel Prize laureates]
* [http://www.ausetute.com.au/elemhist.html History of Elements of the Periodic Table]
* [http://www.chemsoc.org/timeline/pages/timeline.html Chemsoc timeline]