Editing Chemistry (section)

==History==
{{Main|History of chemistry}}
{{For timeline}}
The [[history of chemistry]] spans a period from the ancient past to the present. Since several millennia BC, civilizations were using technologies that would eventually form the basis of the various branches of chemistry. Examples include extracting [[metal]]s from [[ore]]s, making pottery and glazes, fermenting beer and wine, extracting chemicals from plants for medicine and perfume, rendering fat into [[soap]], making [[glass]], and making [[alloy]]s like [[bronze]].

Chemistry was preceded by its protoscience, [[alchemy]], which operated a non-scientific approach to understanding the constituents of matter and their interactions. Despite being unsuccessful in explaining the nature of matter and its transformations, alchemists set the stage for modern chemistry by performing experiments and recording the results. [[Robert Boyle]], although skeptical of elements and convinced of alchemy, played a key part in elevating the "sacred art" as an independent, fundamental and philosophical discipline in his work ''[[The Sceptical Chymist]]'' (1661).<ref name=":0">{{Cite journal |last=Principe |first=L. |date=2011 |title=In retrospect: The Sceptical Chymist |journal=Nature |language=en |volume=469 |issue=7328 |pages=30–31 |doi=10.1038/469030a |bibcode=2011Natur.469...30P |s2cid=6490305 |issn=1476-4687|doi-access=free }}</ref>

While both alchemy and chemistry are concerned with matter and its transformations, the crucial difference was given by the [[scientific method]] that [[chemist]]s employed in their work. Chemistry, as a body of knowledge distinct from alchemy, became an established science with the work of [[Antoine Lavoisier]], who developed a law of [[conservation of mass]] that demanded careful measurement and quantitative observations of chemical phenomena. The history of chemistry afterwards is intertwined with the [[history of thermodynamics]], especially through the work of [[Willard Gibbs]].<ref>{{Cite web |url=http://web.lemoyne.edu/~giunta/papers.html |title=Selected Classic Papers from the History of Chemistry |access-date=8 October 2017 |archive-date=17 September 2018 |archive-url=https://web.archive.org/web/20180917214900/http://web.lemoyne.edu/~giunta/papers.html |url-status=live }}</ref>

===Definition===
The definition of chemistry has changed over time, as new discoveries and theories add to the functionality of the science. The term "chymistry", in the view of noted scientist [[Robert Boyle]] in 1661, meant the subject of the material principles of mixed bodies.<ref>{{Cite book |last=Boyle |first=Robert |title=The Sceptical Chymist |publisher=Dover Publications, Incorporated (reprint) |year=1661 |isbn=978-0-486-42825-3 |location=New York}}</ref> In 1663, the chemist [[Christopher Glaser]] described "chymistry" as a scientific art, by which one learns to dissolve bodies, and draw from them the different substances on their composition, and how to unite them again, and exalt them to a higher perfection.<ref>{{Cite book| last=Glaser | first = Christopher |title= Traite de la chymie|location=Paris | year=1663}} as found in: {{Cite book| last = Kim | first = Mi Gyung | title = Affinity, That Elusive Dream – A Genealogy of the Chemical Revolution | publisher = The MIT Press | year = 2003 | isbn = 978-0-262-11273-4}}
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The 1730 definition of the word "chemistry", as used by [[Georg Ernst Stahl]], meant the art of resolving mixed, compound, or aggregate bodies into their principles; and of composing such bodies from those principles.<ref>{{Cite book |last=Stahl |first=George |title=Philosophical Principles of Universal Chemistry |year=1730 |location=London, England}}</ref> In 1837, [[Jean-Baptiste Dumas]] considered the word "chemistry" to refer to the science concerned with the laws and effects of molecular forces.<ref>Dumas, J. B. (1837). 'Affinite' (lecture notes), vii, p. 4. "Statique chimique", Paris, France: Académie des Sciences.</ref> This definition further evolved until, in 1947, it came to mean the science of substances: their structure, their properties, and the reactions that change them into other substances—a characterization accepted by [[Linus Pauling]].<ref>{{Cite book | last = Pauling | first = Linus | title = General Chemistry | publisher = Dover Publications, Inc. | year = 1947 | isbn = 978-0-486-65622-9 | url = https://archive.org/details/generalchemistry00paul_0 }}</ref> More recently, in 1998, Professor [[Raymond Chang (chemist)|Raymond Chang]] broadened the definition of "chemistry" to mean the study of matter and the changes it undergoes.<ref>{{Cite book|author=Chang, Raymond |title=Chemistry, 6th Ed.|location=New York | publisher=McGraw Hill|year=1998|isbn=978-0-07-115221-1}}</ref>

===Background===
{{See also|Alchemy}}
[[File:Epicurus Louvre.jpg|thumb|upright=0.8|[[Democritus]]' atomist philosophy was later adopted by [[Epicurus]] (341–270 BCE).]]
Early civilizations, such as the [[Ancient Egypt|Egyptians]],<ref>[https://www.newscientist.com/article/mg16121734.300-first-chemists.html First chemists], {{Webarchive|url=https://web.archive.org/web/20150108102557/http://www.newscientist.com/article/mg16121734.300-first-chemists.html|date=8 January 2015}}, February 13, 1999, New Scientist.</ref> [[Mesopotamia|Babylonians]], and [[History of metallurgy in the Indian subcontinent|Indians]],<ref>{{cite book|title=Textiles in Indian Ocean Societies|year=2004|url=https://archive.org/details/textilesindianoc00barn|url-access=limited|first=Ruth|last=Barnes|page=[https://archive.org/details/textilesindianoc00barn/page/n15 1]|publisher=Routledge|isbn=978-0415297660}}</ref> amassed practical knowledge concerning the arts of metallurgy, pottery and dyes, but did not develop a systematic theory.

A basic chemical hypothesis first emerged in [[Classical Greece]] with the theory of [[four elements]] as propounded definitively by [[Aristotle]] stating that [[fire (classical element)|fire]], [[air (classical element)|air]], [[earth (classical element)|earth]] and [[water (classical element)|water]] were the fundamental elements from which everything is formed as a combination. [[Ancient Greece|Greek]] [[atomism]] dates back to 440 BC, arising in works by philosophers such as [[Democritus]] and [[Epicurus]]. In 50 BCE, the [[Ancient Rome|Roman]] philosopher [[Lucretius]] expanded upon the theory in his poem ''[[De rerum natura]]'' (On The Nature of Things).<ref>{{cite web|url=http://classics.mit.edu/Carus/nature_things.html|title=de Rerum Natura (On the Nature of Things)|last=Lucretius|publisher=Massachusetts Institute of Technology|work=The Internet Classics Archive|access-date=9 January 2007|archive-date=29 June 2011|archive-url=https://web.archive.org/web/20110629083541/http://classics.mit.edu/Carus/nature_things.html|url-status=live}}</ref><ref>{{cite web|last=Simpson|first=David|title=Lucretius (c. 99–55 BCE)|work=The Internet History of Philosophy|date=29 June 2005|url=https://iep.utm.edu/lucretiu/|access-date=10 November 2020|archive-date=28 May 2010|archive-url=https://web.archive.org/web/20100528115353/http://www.utm.edu/research/iep/l/lucretiu.htm|url-status=live}}</ref> Unlike modern concepts of science, Greek atomism was purely philosophical in nature, with little concern for empirical observations and no concern for chemical experiments.<ref>{{cite book|last=Strodach|first=George K.|title=The Art of Happiness|year=2012|publisher=Penguin Classics|isbn=978-0-14-310721-7|pages=7–8|location=New York}}</ref>

An early form of the idea of [[conservation of mass]] is the notion that "[[Creatio ex materia|Nothing comes from nothing]]" in [[Ancient Greek philosophy]], which can be found in [[Empedocles]] (approx. 4th century BC): "For it is impossible for anything to come to be from what is not, and it cannot be brought about or heard of that what is should be utterly destroyed."<ref>Fr. 12; see pp. 291–292 of {{Cite book |last1=Kirk |first1=G. S. |title=The Presocratic Philosophers |last2=Raven |first2=J. E. |last3=Schofield |first3=Malcolm |publisher=[[Cambridge University Press]] |year=1983 |isbn=978-0-521-27455-5 |edition=2nd |location=Cambridge}}</ref> and [[Epicurus]] (3rd century BC), who, describing the nature of the Universe, wrote that "the totality of things was always such as it is now, and always will be".<ref>{{Cite book |last1=Long |first1=A. A. |title=The Hellenistic Philosophers. Vol 1: Translations of the principal sources with philosophical commentary |last2=Sedley |first2=D. N. |publisher=Cambridge University Press |year=1987 |isbn=978-0-521-27556-9 |location=Cambridge |pages=25–26 |chapter=Epicureanism: The principals of conservation}}</ref>

[[File:Al-Jaahith - African Arab Naturalist - Basra - al jahiz.jpg|thumb|left|upright=.8|15th-century artistic impression of [[Jābir ibn Hayyān]] (Geber), a [[Alchemy and chemistry in Islam|Perso-Arab alchemist]] and pioneer in [[organic chemistry]]]]
In the [[Hellenistic world]] the art of alchemy first proliferated, mingling magic and occultism into the study of natural substances with the ultimate goal of transmuting elements into [[gold]] and discovering the elixir of eternal life.<ref>{{cite web| url=http://www.laboratory-journal.com/science/chemistry-physics/international-year-chemistry-history-chemistry | title=International Year of Chemistry – The History of Chemistry|publisher=G.I.T. Laboratory Journal Europe|date=25 February 2011|access-date=12 March 2013|url-status=dead|archive-url=https://web.archive.org/web/20130615150135/http://www.laboratory-journal.com/science/chemistry-physics/international-year-chemistry-history-chemistry|archive-date=15 June 2013}}</ref> Work, particularly the development of [[distillation]], continued in the early [[Byzantine]] period with the most famous practitioner being the 4th century Greek-Egyptian [[Zosimos of Panopolis]].<ref>{{cite book |last1=Bunch |first1=Bryan H. |url=https://archive.org/details/isbn_9780618221233/page/88 |title=The History of Science and Technology |last2=Hellemans |first2=Alexander |publisher=Houghton Mifflin Harcourt |year=2004 |isbn=978-0-618-22123-3 |page=[https://archive.org/details/isbn_9780618221233/page/88 88] |name-list-style=amp}}</ref> Alchemy continued to be developed and practised throughout the [[Arab world]] after the [[Early Muslim conquests|Muslim conquests]],<ref>[[Morris Kline]] (1985) [https://books.google.com/books?id=f-e0bro-0FUC&pg=PA284 ''Mathematics for the nonmathematician'']. {{Webarchive|url=https://web.archive.org/web/20150905200134/https://books.google.com/books?id=f-e0bro-0FUC&pg=PA284&dq&hl=en|date=5 September 2015}}. Courier Dover Publications. p. 284. {{ISBN|0-486-24823-2}}.</ref> and from there, and from the Byzantine remnants,<ref>[[Marcelin Berthelot]], [[iarchive:collectiondesanc01bert|''Collection des anciens alchimistes grecs'']] (3 vol., Paris, France, 1887–1888, p. 161); F. Sherwood Taylor, "The Origins of Greek Alchemy", ''Ambix'' 1 (1937), p. 40.</ref> diffused into medieval and [[Renaissance]] Europe through Latin translations.

The Arabic works attributed to [[Jabir ibn Hayyan]] introduced a systematic classification of chemical substances, and provided instructions for deriving an inorganic compound ([[sal ammoniac]] or [[ammonium chloride]]) from [[Organic compound|organic substances]] (such as plants, blood, and hair) by chemical means.<ref>{{cite journal <!-- Citation bot bypass--> |last1=Stapleton |first1=Henry Enest |author1-link=Henry Ernest Stapleton |last2=Azo |first2=R. F. |last3=Hidayat Husain |first3=M. |year=1927 |title=Chemistry in Iraq and Persia in the Tenth Century A.D. |url=http://www.southasiaarchive.com/Content/sarf.100203/231270 |journal=Memoirs of the Asiatic Society of Bengal |volume=VIII |issue=6 |pages=317–418 |oclc=706947607}} pp. 338–340; {{Cite book |last=Kraus |first=Paul |author-link=Paul Kraus (Arabist) |title=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 |publisher=Institut Français d'Archéologie Orientale |year=1942–1943 |isbn=978-3-487-09115-0 |location=Cairo |oclc=468740510}} vol. II, pp. 41–42.</ref> Some Arabic Jabirian works (e.g., the "Book of Mercy", and the "Book of Seventy") were later translated into Latin under the [[Latinisation of names|Latinized]] name "Geber",<ref>Darmstaedter, Ernst. "Liber Misericordiae Geber: Eine lateinische Übersetzung des gröβeren Kitâb l-raḥma", ''Archiv für Geschichte der Medizin'', 17/4, 1925, pp. 181–197; Berthelot, Marcellin. "Archéologie et Histoire des sciences", ''Mémoires de l'Académie des sciences de l'Institut de France'', 49, 1906, pp. 308–363; see also Forster, Regula. [https://referenceworks.brillonline.com/entries/encyclopaedia-of-islam-3/jabir-b-hayyan-COM_32665 "Jābir b. Ḥayyān"], {{Webarchive|url=https://web.archive.org/web/20210418013644/https://referenceworks.brillonline.com/entries/encyclopaedia-of-islam-3/jabir-b-hayyan-COM_32665|date=18 April 2021}}, ''Encyclopaedia of Islam, Three''.</ref> and in 13th-century Europe an anonymous writer, usually referred to as [[pseudo-Geber]], started to produce alchemical and metallurgical writings under this name.<ref>Newman, William R. "New Light on the Identity of Geber", ''Sudhoffs Archiv'', 1985, 69, pp. 76–90; Newman, William R. ''The Summa perfectionis of Pseudo-Geber: A critical ed., translation and study'', Leiden: Brill, 1991, pp. 57–103. It has been argued by Ahmad Y. Al-Hassan that the pseudo-Geber works were actually translated into Latin from the Arabic (see Al-Hassan, Ahmad Y. "The Arabic Origin of the ''Summa'' and Geber Latin Works: A Refutation of Berthelot, Ruska, and Newman Based on Arabic Sources", in: Ahmad Y. Al-Hassan. ''Studies in al-Kimya': Critical Issues in Latin and Arabic Alchemy and Chemistry''. Hildesheim: Georg Olms Verlag, 2009, pp. 53–104; also available [http://www.history-science-technology.com/geber/geber%2004.html online]. {{Webarchive|url=https://web.archive.org/web/20210225044920/http://www.history-science-technology.com/geber/geber%2004.html|date=25 February 2021}}).</ref> Later influential Muslim philosophers, such as [[Abū al-Rayhān al-Bīrūnī]]<ref>{{cite journal | doi = 10.2307/2851429 | last1 = Marmura | first1 = Michael E. | last2 = Nasr | first2 = Seyyed Hossein| year = 1965 | title = ''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 | jstor = 2851429| journal = Speculum | volume = 40 | issue = 4| pages = 744–746 | title-link = Hossein Nasr }}</ref> and [[Avicenna]]<ref>[[Robert Briffault]] (1938). ''The Making of Humanity'', pp. 196–197.</ref> disputed the theories of alchemy, particularly the theory of the [[Philosopher's stone|transmutation of metals]].

[[File:Georgius Agricola.jpg|thumb|upright=0.8|[[Georgius Agricola]], author of ''[[De re metallica]]'', was the first to drop the Arabic definite article ''al-'', exclusively writing ''chymia'' and ''chymista'', giving chemistry its modern name.<ref name="Hexagon2005">{{cite journal |last1=Marshall |first1=James L. |last2=Marshall |first2=Virginia R. |title=Rediscovery of the Elements: Agricola |journal=The Hexagon |date=Autumn 2005 |volume=96 |issue=3 |page=59 |url=https://chemistry.unt.edu/sites/default/files/users/owj0001/agricola.pdf |access-date=7 January 2024 |publisher=Alpha Chi Sigma |issn=0164-6109 |oclc=4478114}}</ref><ref name="berk" /><ref name="Rafferty 2012 p. 10" />]]
Improvements of the refining of ores and their extractions to smelt metals was widely used source of information for early chemists in the 16th century, among them [[Georg Agricola]] (1494–1555), who published his major work ''[[De re metallica]]'' in 1556. His work, describing highly developed and complex processes of mining metal ores and metal extraction, were the pinnacle of metallurgy during that time. His approach removed all mysticism associated with the subject, creating the practical base upon which others could and would build. The work describes the many kinds of furnaces used to smelt ore, and stimulated interest in minerals and their composition. Agricola has been described as the "father of metallurgy" and the founder of [[geology]] as a scientific discipline.<ref>[[Karl Alfred von Zittel]] (1901). ''History of Geology and Palaeontology'', p. 15.</ref><ref name="berk">{{cite web |title=Georgius Agricola |url=https://ucmp.berkeley.edu/history/agricola.html |access-date=4 April 2019 |publisher=University of California – Museum of Paleontology}}</ref><ref name="Rafferty 2012 p. 10">Rafferty, John P. (2012). ''Geological Sciences; Geology: Landforms, Minerals, and Rocks''. New York: Britannica Educational Publishing, p. 10. {{ISBN|9781615305445}}</ref>

Under the influence of the [[scientific revolution|new empirical methods]] propounded by [[Sir Francis Bacon]] and others, a group of chemists at [[Oxford]], [[Robert Boyle]], [[Robert Hooke]] and [[John Mayow]] began to reshape the old alchemical traditions into a scientific discipline. Boyle in particular questioned some commonly held chemical theories and argued for chemical practitioners to be more "philosophical" and less commercially focused in ''[[The Sceptical Chymist|The Sceptical Chemyst]]''.<ref name=":0" /> He formulated [[Boyle's law]], rejected the classical "four elements" and proposed a mechanistic alternative of atoms and [[chemical reaction]]s that could be subject to rigorous experiment.<ref>{{cite web |url=https://www.bbc.co.uk/history/historic_figures/boyle_robert.shtml |title=History – Robert Boyle (1627–1691) |publisher=BBC |access-date=12 June 2011 |archive-date=9 January 2011 |archive-url=https://web.archive.org/web/20110109090458/http://www.bbc.co.uk/history/historic_figures/boyle_robert.shtml |url-status=live }}</ref>

[[File:David - Portrait of Monsieur Lavoisier (cropped).jpg|thumb|upright=0.8|[[Antoine-Laurent de Lavoisier]] is considered the "Father of Modern Chemistry".<ref>{{Cite journal |last1=Eagle |first1=Cassandra T. |last2=Sloan |first2=Jennifer |year=1998 |title=Marie Anne Paulze Lavoisier: The Mother of Modern Chemistry |journal=The Chemical Educator |volume=3 |issue=5 |pages=1–18 |doi=10.1007/s00897980249a |s2cid=97557390}}</ref>]]
In the following decades, many important discoveries were made, such as the nature of 'air' which was discovered to be composed of many different gases. The Scottish chemist [[Joseph Black]] and the Flemish [[Jan Baptist van Helmont]] discovered [[carbon dioxide]], or what Black called 'fixed air' in 1754; [[Henry Cavendish]] discovered [[hydrogen]] and elucidated its properties and [[Joseph Priestley]] and, independently, [[Carl Wilhelm Scheele]] isolated pure [[oxygen]]. The theory of [[phlogiston]] (a substance at the root of all combustion) was propounded by the German [[Georg Ernst Stahl]] in the early 18th century and was only overturned by the end of the century by the French chemist [[Antoine Lavoisier]], the chemical analogue of Newton in physics. Lavoisier did more than any other to establish the new science on proper theoretical footing, by elucidating the principle of [[conservation of mass]] and developing a new system of chemical nomenclature used to this day.<ref>{{Cite book |author=Kim |first=Mi Gyung |url=https://archive.org/details/affinitythatelus00kimm_807 |title=Affinity, that Elusive Dream: A Genealogy of the Chemical Revolution |publisher=MIT Press |year=2003 |isbn=978-0-262-11273-4 |page=[https://archive.org/details/affinitythatelus00kimm_807/page/n454 440] |url-access=limited}}</ref>

English scientist [[John Dalton]] proposed the modern [[atomic theory|theory of atoms]]; that all substances are composed of indivisible 'atoms' of matter and that different atoms have varying atomic weights.

The development of the electrochemical theory of chemical combinations occurred in the early 19th century as the result of the work of two scientists in particular, [[Jöns Jacob Berzelius]] and [[Humphry Davy]], made possible by the prior invention of the [[voltaic pile]] by [[Alessandro Volta]]. Davy discovered nine new elements including the [[alkali metals]] by extracting them from their [[oxide]]s with electric current.<ref>{{cite journal|first=Humphry|last=Davy|title=On some new Phenomena of Chemical Changes produced by Electricity, particularly the Decomposition of the fixed Alkalies, and the Exhibition of the new Substances, which constitute their Bases|pages=1–45|year=1808|volume=98|journal=Philosophical Transactions of the Royal Society|url=https://books.google.com/books?id=Kg9GAAAAMAAJ|doi=10.1098/rstl.1808.0001|doi-access=free|access-date=30 November 2020|archive-date=18 April 2021|archive-url=https://web.archive.org/web/20210418022330/https://books.google.com/books?id=Kg9GAAAAMAAJ|url-status=live}}</ref>

[[File:Дмитрий Иванович Менделеев 4.gif|thumb|left|In his periodic table, [[Dmitri Mendeleev]] predicted the existence of 7 new elements,<ref>{{cite web|work=Chemistry 412 course notes|title=A Brief History of the Development of Periodic Table|publisher=Western Oregon University|url=https://people.wou.edu/~courtna/ch412/perhist.htm|access-date=20 July 2015|archive-date=9 February 2020|archive-url=https://web.archive.org/web/20200209103433/https://people.wou.edu/~courtna/ch412/perhist.htm|url-status=live}}</ref> and placed all 60 elements known at the time in their correct places.<ref>[http://www.rsc.org/education/teachers/resources/periodictable/pre16/develop/index.htm Note]. {{Webarchive|url=https://web.archive.org/web/20150924141037/http://www.rsc.org/education/teachers/resources/periodictable/pre16/develop/index.htm|date=24 September 2015}}. "...it is surely true that had Mendeleev never lived modern chemists would be using a Periodic Table" and {{cite web |title=Dmitri Mendeleev |url=http://www.rsc.org/education/teachers/resources/periodictable/pre16/develop/mendeleev.htm |url-status=live |archive-url=https://archive.today/20140702202659/http://www.rsc.org/education/teachers/resources/periodictable/pre16/develop/mendeleev.htm |archive-date=2 July 2014 |access-date=18 July 2015 |publisher=Royal Society of Chemistry}}</ref>]]
British [[William Prout]] first proposed ordering all the elements by their atomic weight as all atoms had a weight that was an exact multiple of the atomic weight of hydrogen. [[J.A.R. Newlands]] devised an early table of elements, which was then developed into the modern [[periodic table]] of elements<ref name="WebElements_dot_com">{{cite web
| url         = http://www.webelements.com/
| title       = WebElements: the periodic table on the web
| last        = Winter
| first       = Mark
| publisher   = The [[University of Sheffield]]
| access-date = 27 January 2014
| archive-date= 4 January 2014
| archive-url  = https://web.archive.org/web/20140104110225/http://webelements.com/
| url-status  = live
}}</ref> in the 1860s by [[Dmitri Mendeleev]] and independently by several other scientists including [[Julius Lothar Meyer]].<ref>{{cite web|url=https://www.sciencehistory.org/historical-profile/julius-lothar-meyer-and-dmitri-ivanovich-mendeleev|title=Julius Lothar Meyer and Dmitri Ivanovich Mendeleev|publisher=Science History Institute|access-date=20 March 2018|date=June 2016|archive-date=21 March 2018|archive-url=https://web.archive.org/web/20180321130939/https://www.sciencehistory.org/historical-profile/julius-lothar-meyer-and-dmitri-ivanovich-mendeleev|url-status=live}}</ref><ref>"What makes these family likenesses among the elements? In the 1860s everyone was scratching their heads about that, and several scientists moved towards rather similar answers. The man who solved the problem most triumphantly was a young Russian called Dmitri Ivanovich Mendeleev, who visited the salt mine at Wieliczka in 1859." {{cite book|title=The Ascent of Man|author=Bronowski, Jacob|publisher=Little, Brown and Company|isbn=978-0-316-10930-7|year=1973|page=[https://archive.org/details/ascentofmanbron00bron/page/322 322]|url=https://archive.org/details/ascentofmanbron00bron/page/322}}</ref> The inert gases, later called the [[noble gas]]es were discovered by [[William Ramsay]] in collaboration with [[Lord Rayleigh]] at the end of the century, thereby filling in the basic structure of the table.

Organic chemistry was developed by [[Justus von Liebig]] and others, following [[Friedrich Wöhler]]'s synthesis of [[urea]].<ref>{{Cite book| title = The Development of Modern Chemistry | author = Ihde, Aaron John | publisher = Courier Dover Publications | year = 1984 | page = 164 | isbn = 978-0-486-64235-2}}</ref> Other crucial 19th century advances were; an understanding of valence bonding ([[Edward Frankland]] in 1852) and the application of thermodynamics to chemistry ([[J. W. Gibbs]] and [[Svante Arrhenius]] in the 1870s).

[[File:Rutherford gold foil experiment results.svg|right|upright|thumb|''Top:'' Expected results: [[alpha particle]]s passing through the [[plum pudding model]] of the atom undisturbed.<br>
''Bottom:'' Observed results: a small portion of the particles were deflected, indicating [[Atomic nucleus|a small, concentrated charge]].]]
At the turn of the twentieth century the theoretical underpinnings of chemistry were finally understood due to a series of remarkable discoveries that succeeded in probing and discovering the very nature of the internal structure of atoms. In 1897, [[J.J. Thomson]] of the [[University of Cambridge]] discovered the [[electron]] and soon after the French scientist [[Becquerel]] as well as the couple [[Pierre Curie|Pierre]] and [[Marie Curie]] investigated the phenomenon of [[radioactivity]]. In a series of pioneering scattering experiments [[Ernest Rutherford]] at the [[University of Manchester]] discovered the internal structure of the atom and the existence of the proton, classified and explained the different types of radioactivity and successfully [[Nuclear transmutation|transmuted]] the first element by bombarding [[nitrogen]] with [[alpha particle]]s.

His work on atomic structure was improved on by his students, the Danish physicist [[Niels Bohr]], the Englishman [[Henry Moseley]] and the German [[Otto Hahn]], who went on to father the emerging [[nuclear chemistry]] and discovered [[nuclear fission]]. The electronic theory of [[chemical bond]]s and [[molecular orbital]]s was developed by the American scientists [[Linus Pauling]] and [[Gilbert N. Lewis]].

The year 2011 was declared by the United Nations as the International Year of Chemistry.<ref>{{cite web |url=http://www.chemistry2011.org |title=Chemistry |publisher=Chemistry2011.org |access-date=10 March 2012 |archive-url=https://web.archive.org/web/20111008032346/http://www.chemistry2011.org/ |archive-date=8 October 2011 |url-status=dead }}</ref> It was an initiative of the International Union of Pure and Applied Chemistry, and of the United Nations Educational, Scientific, and Cultural Organization and involves chemical societies, academics, and institutions worldwide and relied on individual initiatives to organize local and regional activities.