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| | The considered consuming green coffee bean extract to begin losing weight may possibly appear surprisingly new nevertheless it has absolutely aided a ideal deal of individuals go back to their wonderful weight plus more. Losing fat is never a easy thing to strive for. Besides the undeniable truth that it usually need a great deal of effort plus discipline, 1 is not actually sure when the several products being presented available is effective o-r not. The question today is, can this extract be an perfect method to lose excess fat? Can it be secure? How rapidly may one really see results? Keep reading plus discover.<br><br>Chlorogenic acid is the name of the all-natural compound found in the [http://greencoffeeweightlossplan.blogspot.com green coffee weight loss] s. This valuable natural component is destroyed in the task of roasting. Dr. Lindsey Duncan is a Neuropathic Doctor plus Certified Nutritionist and was the guest of Dr. Oz in his April, 2012 show. Both of these experts endorse green coffee fat loss Extract (GCBE) because an powerful plus excellent natural way to securely lose weight. The value of utilizing only 100 per % Pure GCBE with no additives cannot be overly stressed. Even the capsule should be vegetable based.<br><br>Chlorogenic acid plays an significant role inside the metabolism. It slows down the release of glucose following the meal. This stops fat from being produced which assists with a weight reduction efforts. It boosts your metabolism plus enables we to attain higher rates of burned up calories. Higher the number of calories burned, higher is the weight reduction.<br><br>Many of the practitioners and analysis experts are wondering how can a coffee is produced to lower the excess fat! They were beneath shock whenever it was experimentally proven. Folks will consume this product and employ inside their daily because a dietary supplement.<br><br>Considering that the liver plays a major character inside keeping a weight under control by regulating fat metabolism and pumping excessive fat out through the bile and into the little intestines, it is very both a "fat burning" plus a "fat pumping" organ.<br><br>However you need to always remain hydrated particularly whenever you're continually losing fat, drinking 2 to 3 litres of water a day is suggested to avoid severe illness.<br><br>2) It has been shown to inhibit an important enzyme found inside the liver which is needed to break down glycogen: glucose-6-phosphatase (G6P). Now this has been shown inside the lab[2], however not yet in a living animal, thus how do we learn it really does inhibit G6P whenever eaten? Well it has not been straight demonstrated, yet scientists have shown which chlorogenic acid is absorbed into the blood, through the belly without getting degraded in rats[3]. So it happens to be reasonable to assume that it arrives at the liver intact, where is can reach work inhibiting G6P.<br><br>Finally, you're going to should stick to the aged diet-and-exercise system. It is not difficult to get the suggested amount of exercise, nevertheless it is actually vital which you do so. The same is true for eating the appropriate amount of fruits plus veggies. If you're certainly concerned with the ability to stick to a program, a fat reduction diary may be a desirable resource. Visit the linked website to learn more about green coffee pure. |
| {{Redirect|Chemical science|the Royal Society of Chemistry journal|Chemical Science (journal)}}
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| [[Image:Chemicals in flasks.jpg|thumb|right|Chemicals in flasks (including [[ammonium hydroxide]] and [[nitric acid]]) lit in different colors]]
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| {{science}}
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| '''Chemistry''', a branch of [[physical science]], is the study of the composition, structure, properties and change of [[matter]].<ref name=definition>{{cite web|url=http://chemweb.ucc.ie/what_is_chemistry.htm |title=What is Chemistry? |publisher=Chemweb.ucc.ie |date= |accessdate=2011-06-12}}</ref><ref>[http://dictionary.reference.com/browse/Chemistry Chemistry]. (n.d.). Merriam-Webster's Medical Dictionary. Retrieved August 19, 2007.</ref> Chemistry is chiefly concerned with [[atom]]s and their interactions with other atoms - for example, the properties of the [[chemical bond]]s formed between atoms to create [[chemical compound]]s. As well as this, interactions including atoms and other phenomena—[[electron]]s and various forms of [[energy]]—are considered, such as [[photochemical reaction]]s, [[redox|oxidation-reduction reactions]], [[Phase transition|changes in phases of matter]], and [[Separation process|separation of mixtures]]. Finally, properties of matter such as [[alloy]]s or [[polymer]]s are considered.
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| Chemistry is sometimes called "[[the central science]]" because it bridges other [[natural sciences]] like [[physics]], [[geology]] and [[biology]] with each other.<ref>Theodore L. Brown, H. Eugene Lemay, Bruce Edward Bursten, H. Lemay. ''Chemistry: The Central Science''. Prentice Hall; 8 edition (1999). ISBN 0-13-010310-1. Pages 3–4.</ref><ref>Chemistry is seen as occupying an intermediate position in a hierarchy of the sciences by "reductive level" between physics and biology. See Carsten Reinhardt. ''Chemical Sciences in the 20th Century: Bridging Boundaries''. Wiley-VCH, 2001. ISBN 3-527-30271-9. Pages 1–2.</ref> Chemistry is a branch of [[physical science]] but [[Difference between chemistry and physics|distinct from physics]].<ref>{{cite doi|10.1007/BF01801556}}</ref>
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| The etymology of the word chemistry has been much disputed.<ref>'''See:''' [[Chemistry (etymology)]] for possible origins of this word.</ref> The [[history of chemistry|origin of chemistry]] can be traced to certain practices, known as [[alchemy]], which had been practiced for several [[millennia]] in various parts of the world, particularly the Middle East.<ref>http://etext.lib.virginia.edu/cgi-local/DHI/dhi.cgi?id=dv1-04</ref>
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| ==Etymology==
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| {{TopicTOC-Chemistry}}
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| {{Main|Chemistry (word)}}
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| The word ''chemistry'' comes from the word ''alchemy'', an earlier set of practices that encompassed elements of chemistry, metallurgy, philosophy, astrology, astronomy, mysticism and medicine; it is commonly thought of as the quest to turn lead or another common starting material into gold.<ref>{{cite web|url=http://www.alchemylab.com/history_of_alchemy.htm |title=History of Alchemy |publisher=Alchemy Lab |date= |accessdate=2011-06-12}}</ref> Alchemy, which was practiced around 330, is the study of the composition of waters, movement, growth, embodying, disembodying, drawing the spirits from bodies and bonding the spirits within bodies ([[Zosimos of Panopolis|Zosimos]]).<ref>Strathern, P. (2000). ''Mendeleyev's Dream – the Quest for the Elements.'' New York: Berkley Books.</ref> An alchemist was called a 'chemist' in popular speech, and later the suffix "-ry" was added to this to describe the art of the chemist as "chemistry".
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| The word ''alchemy'' in turn is derived from the [[Arabic language|Arabic]] <nowiki/>word ''al-kīmīā'' (الکیمیاء). In origin, the term is borrowed from the Greek χημία or χημεία.<ref name=oed>"alchemy", entry in ''The Oxford English Dictionary'', J. A. Simpson and E. S. C. Weiner, vol. 1, 2nd ed., 1989, ISBN 0-19-861213-3.</ref><ref>p. 854, "Arabic alchemy", Georges C. Anawati, pp. 853–885 in ''Encyclopedia of the history of Arabic science'', eds. Roshdi Rashed and Régis Morelon, London: Routledge, 1996, vol. 3, ISBN 0-415-12412-3.</ref> This may have [[Ancient Egypt|Egyptian]] origins. Many believe that ''al-kīmīā'' is derived from the Greek χημία, which is in turn derived from the word '''Chemi''' or '''Kimi''', which is the ancient name of [[Egypt]] in [[Egyptian language|Egyptian]].<ref name=oed /> Alternately, ''al-kīmīā'' may be derived from χημεία, meaning "cast together".<ref>Weekley, Ernest (1967). Etymological Dictionary of Modern English. New York: Dover Publications. ISBN 0-486-21873-2</ref>
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| ===Definition===
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| In retrospect, 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|location=New York | publisher=Dover Publications, Inc. (reprint)|year=1661|isbn=0-486-42825-7}}</ref> In 1663, "chymistry" meant 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 - this definition was used by chemist [[Christopher Glaser]].<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 = 0-262-11273-6}}
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| </ref>
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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, E. |title=Philosophical Principles of Universal Chemistry|location=London | year=1730}}</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, pg 4. "Statique chimique", Paris: Academie 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 = 0-486-65622-5}}</ref> More recently, in 1998, the definition of "chemistry" was broadened to mean the study of matter and the changes it undergoes, as phrased by Professor [[Raymond Chang (chemist)|Raymond Chang]].<ref>{{Cite book|author=Chang, Raymond |title=Chemistry, 6th Ed.|location=New York | publisher=McGraw Hill|year=1998|isbn=0-07-115221-0}}</ref>
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| ==History==
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| {{Main|History of chemistry}}
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| {{See also|Alchemy|Timeline of chemistry}}
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| [[Image:Epicurus Louvre.jpg|thumb|200px|[[Democritus]]' atomist philosophy was later adopted by [[Epicurus]] (341–270 BCE).]]
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| Early civilizations, such as the [[Ancient Egypt|Egyptians]]<ref>[http://www.newscientist.com/article/mg16121734.300-first-chemists.html First chemists], February 13, 1999, New Scientist</ref> and [[Mesopotamia|Babylonians]] amassed practical knowledge concerning the arts of metallurgy, pottery and dyes, but didn't develop a systematic theory.
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| A basic chemical hypothesis first emerged in [[Classical Greece]] with the theory of [[four elements]] as propounded definitively by [[Aristotle]] stating that that [[fire]], [[air]], [[earth]] and [[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 BC, the [[Ancient Rome|Roman]] philosopher [[Lucretius]] expanded upon the theory in his book ''[[De rerum natura|De Rerum Natura]]'' (On The Nature of Things).<ref>{{cite web|last=Lucretius|title=de Rerum Natura (On the Nature of Things)|work=The Internet Classics Archive|publisher=Massachusetts Institute of Technology|date=50 BCE|url=http://classics.mit.edu/Carus/nature_things.html|accessdate=2007-01-09}}</ref><ref>{{cite web|last=Simpson|first=David|title=Lucretius (c. 99 - c. 55 BCE)|work=The Internet History of Philosophy|date=29 June 2005|url=http://www.iep.utm.edu/l/lucretiu.htm|accessdate= 2007-01-09}}</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=0-14-310721-6|pages=7–8|location=New York}}</ref>
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| 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=Feb 25, 2011|accessdate=March 12, 2013}}</ref> Alchemy was discovered and practised widely throughout the [[Arab world]] after the [[Muslim Conquest]],<ref>[[Morris Kline]] (1985) [http://books.google.com/books?id=f-e0bro-0FUC&pg=PA284&dq&hl=en#v=onepage&q=&f=false ''Mathematics for the nonmathematician'']. [[Courier Dover Publications]]. p. 284. ISBN 0-486-24823-2</ref> and from there, diffused into medieval and [[Rennaissance]] [[Europe]] through [[Latin]] translations.<ref>[http://www.chemheritage.org/explore/ancients-time.html Alchemy Timeline]{{dead link|date=June 2011}} - Chemical Heritage Society</ref>
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| ===Chemistry as science===
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| 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 achemical traditions into a scientific discipline. Boyle in particular is regarded as the founding father of chemistry due to his most important work, the classic chemistry text ''[[The Sceptical Chymist]]'' where the differentiation is made between the claims of alchemy and the empirical scientific discoveries of the new chemistry.<ref>"Robert Boyle, Founder of Modern Chemistry" Harry Sootin (2011)</ref> He formulated [[Boyle's law]], rejected the classical "four elements" and proposed a mechanistic alternative of atoms and [[chemical reactions]] that could be subject to rigorous experiment.<ref>{{cite web|url=http://www.bbc.co.uk/history/historic_figures/boyle_robert.shtml |title=History - Robert Boyle (1627–1691) |publisher=BBC |date= |accessdate=2011-06-12}}</ref>
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| [[Image:Antoine lavoisier color.jpg|thumb|right|200px|[[Antoine-Laurent de Lavoisier]] is considered the "Father of Modern Chemistry".<ref>{{Cite journal|last=Eagle |first=Cassandra T. |coauthors=Jennifer Sloan |title=Marie Anne Paulze Lavoisier: The Mother of Modern Chemistry |journal=The Chemical Educator |year=1998 |volume=3 |issue=5 |pages=1–18 |format=PDF |accessdate=2007-12-14 |doi=10.1007/s00897980249a }}</ref>]]
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| 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; who 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|title = Affinity, that Elusive Dream: A Genealogy of the Chemical Revolution | author = Mi Gyung Kim | publisher = MIT Press | year = 2003 |page = 440|isbn = 0-262-11273-6}}</ref>
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| Prior to his work, though, many important discoveries had been made, specifically relating to the nature of 'air' which was discovered to be composed of many different gases. The Scottish chemist [[Joseph Black]] (the first experimental chemist) and the Dutchman [[J. B. 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]].
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| English scientist [[John Dalton]] proposed the modern [[atomic theory|theory of atoms]] in his book (1803) ''[[Atomic Theory]]''; that all substances are composed of indivisible 'atoms' of matter and that different atoms have varying atomic weights.
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| 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, [[J. J. 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|issue=0|year=1808|volume=98|journal=Philosophical Transactions of the Royal Society|url=http://books.google.com/?id=Kg9GAAAAMAAJ|doi=10.1098/rstl.1808.0001|publisher=Royal Society of London.}}</ref>
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| 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
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| | url = http://www.webelements.com/
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| | title = WebElements: the periodic table on the web
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| | last = Winter
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| | first = Mark
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| | publisher = The [[University of Sheffield]]
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| | accessdate = January 27, 2014
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| | archivedate = January 04, 2014
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| | archiveurl = http://web.archive.org/web/20140104110225/http://webelements.com/
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| }}</ref> by the German [[Julius Lothar Meyer]] and the Russian [[Dmitri Mendeleev]] in the 1860s.<ref>[http://chemistry.about.com/library/weekly/aa030303a.htm Timeline of Element Discovery] - About.com</ref> The inert gases, later called the [[noble gases]] 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.
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| Organic chemistry was developed by [[Justus von Liebig]] and others, following [[Friedrich Wohler]]'s synthesis of [[urea]] which proved that living organisms were, in theory, reducible to chemistry.<ref>{{Cite book| title = The Development of Modern Chemistry | author = Ihde, Aaron John | publisher = Courier Dover Publications | year = 1984 | page = 164 | isbn = 0-486-64235-6}}</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).
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| ===Chemical structure===
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| [[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>
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| ''Bottom:'' Observed results: a small portion of the particles were deflected, indicating [[Atomic nucleus|a small, concentrated charge]].]]
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| 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 [[Cambridge University]] 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.
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| His work on atomic structure was improved on by his students, the Danish physicist [[Niels Bohr]] and [[Henry Mosely]]. The electronic theory of [[chemical bond]]s and [[molecular orbital]]s was developed by the American scientists [[Linus Pauling]] and [[Gilbert N. Lewis]].
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| 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 |date= |accessdate=2012-03-10}}</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.
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| ==Principles of modern chemistry==
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| [[Image:Lab bench.jpg|thumb|250px|[[Laboratory]], Institute of Biochemistry, [[University of Cologne]].]]
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| The current model of atomic structure is the [[quantum mechanical model]].<ref>{{cite web|title=chemical bonding|url=http://www.britannica.com/EBchecked/topic/684121/chemical-bonding/43383/The-quantum-mechanical-model|work=Britannica|publisher=Encyclopædia Britannica|accessdate=1 November 2012}}</ref> Traditional chemistry starts with the study of [[elementary particles]], [[atom]]s, [[molecule]]s,<ref>[http://www.visionlearning.com/library/module_viewer.php?mid=49 Matter: Atoms from Democritus to Dalton] by Anthony Carpi, Ph.D.</ref> [[chemical substance|substance]]s, metals, [[crystal]]s and other aggregates of matter. This matter can be studied in solid, liquid, or gas [[states of matter|states]], in isolation or in combination. The [[chemical interaction|interactions]], reactions and transformations that are studied in chemistry are usually the result of interactions between atoms, leading to rearrangements of the chemical bonds which hold atoms together. Such behaviors are studied in a chemistry [[laboratory]].
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| The chemistry laboratory stereotypically uses various forms of [[laboratory glassware]]. However glassware is not central to chemistry, and a great deal of experimental (as well as applied/industrial) chemistry is done without it.
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| A [[chemical reaction]] is a transformation of some substances into one or more different substances.<ref>IUPAC [[Gold Book]] [http://www.iupac.org/goldbook/C01033.pdf Definition]</ref> The basis of such a chemical transformation is the rearrangement of electrons in the chemical bonds between atoms. It can be symbolically depicted through a [[chemical equation]], which usually involves atoms as subjects. The number of atoms on the left and the right in the equation for a chemical transformation is equal (when unequal, the transformation by definition is not chemical, but rather a [[nuclear reaction]] or [[radioactive decay]]). The type of chemical reactions a substance may undergo and the energy changes that may accompany it are constrained by certain basic rules, known as chemical laws.
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| [[Energy]] and [[entropy]] considerations are invariably important in almost all chemical studies. Chemical substances are classified in terms of their [[structure]], phase, as well as their [[chemical composition]]s. They can be analyzed using the tools of [[chemical analysis]], e.g. [[spectroscopy]] and [[chromatography]]. Scientists engaged in chemical research are known as [[chemists]].<ref>{{cite web|url=http://www.calmis.ca.gov/file/occguide/CHEMIST.HTM |title=California Occupational Guide Number 22: Chemists |publisher=Calmis.ca.gov |date=1999-10-29 |accessdate=2011-06-12}}</ref> Most chemists specialize in one or more sub-disciplines. Several [[concept]]s are essential for the study of chemistry; some of them are:<ref>{{cite web|url=http://antoine.frostburg.edu/chem/senese/101/matter/ |title=General Chemistry Online - Companion Notes: Matter |publisher=Antoine.frostburg.edu |date= |accessdate=2011-06-12}}</ref>
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| ===Matter===
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| {{Main|Matter}}
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| In chemistry, matter is defined as anything that has [[invariant mass|rest mass]] and [[volume]] (it takes up space) and is made up of [[particle]]s. The particles that make up matter have rest mass as well - not all particles have rest mass, such as the [[photon]]. Matter can be a pure [[chemical substance]] or a [[mixture]] of substances.<ref>{{cite book |last=Armstrong |first=James |title=General, Organic, and Biochemistry: An Applied Approach |publisher=[[Brooks/Cole]] |year=2012 |isbn=978-0-534-49349-3 |page=48}}</ref>
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| ====Atom====
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| [[File:Atom diagram.png|thumb|170px|left|A diagram of an atom based on the [[Rutherford model]]]]
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| The atom is the basic unit of chemistry. It consists of a dense core called the [[atomic nucleus]] surrounded by a space called the [[electron cloud]]. The nucleus is made up of positively charged [[protons]] and uncharged [[neutrons]] (together called [[nucleon]]s), while the electron cloud consists of negatively-charged [[electron]]s which orbit the nucleus. In a neutral atom, the negatively-charged electrons balance out the positive charge of the protons. The nucleus is dense; the mass of a nucleon is 1,836 times that of an electron, yet the radius of an atom is about 10,000 times that of its nucleus.{{sfn|Burrows|Holman|Parsons|Pilling|2008|p=13}}{{sfn|Housecroft|Sharpe|2008|p=2}}
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| The atom is also the smallest entity that can be envisaged to retain the [[chemical properties]] of the element, such as [[electronegativity]], [[ionization potential]], preferred [[oxidation state]](s), [[coordination number]], and preferred types of bonds to form (e.g., [[metallic]], [[ion]]ic, [[covalent]]).
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| ====Element====
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| [[File:Periodic table (polyatomic).svg|thumb|right|300px|Standard form of the [[periodic table]] of chemical elements. The colors represent different categories of elements]]
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| {{Main|Chemical element}}
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| A chemical element is a pure substance which is composed of a single type of atom, characterized by its particular number of [[proton]]s in the nuclei of its atoms, known as the [[atomic number]] and represented by the symbol ''Z''. The [[mass number]] is the sum of the number of protons and neutrons in a nucleus. Although all the nuclei of all atoms belonging to one element will have the same atomic number, they may not necessarily have the same mass number; atoms of an element which have different mass numbers are known as [[isotope]]s. For example, all atoms with 6 protons in their nuclei are atoms of the chemical element [[carbon]], but atoms of carbon may have mass numbers of 12 or 13.{{sfn|Housecroft|Sharpe|2008|p=2}}
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| The standard presentation of the chemical elements is in the [[periodic table]], which orders elements by atomic number. The periodic table is arranged in [[Periodic table group|groups]], or columns, and [[period (periodic table)|periods]], or rows. The periodic table is useful in identifying [[periodic trends]].{{sfn|Burrows|Holman|Parsons|Pilling|2009|p=110}}
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| ====Compound====
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| [[File:Carbon dioxide structure.png|thumb|left|130px|[[Carbon dioxide]] (CO<sub>2</sub>), an example of a chemical compound]]
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| {{Main|Chemical compound}}
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| A ''compound'' is a pure chemical substance composed of more than one element. The properties of a compound bear little similarity to those of its elements.{{sfn|Burrows|Holman|Parsons|Pilling|2008|p=12}} The standard nomenclature of compounds is set by the [[International Union of Pure and Applied Chemistry]] (IUPAC). [[Organic compound]]s are named according to the [[organic nomenclature]] system.<ref>{{cite web|url=http://www.acdlabs.com/iupac/nomenclature/ |title=IUPAC Nomenclature of Organic Chemistry |publisher=Acdlabs.com |date= |accessdate=2011-06-12}}</ref> [[Inorganic compound]]s are named according to the [[inorganic nomenclature]] system.<ref>IUPAC Provisional Recommendations for the Nomenclature of Inorganic Chemistry (2004) [http://www.iupac.org/reports/provisional/abstract04/connelly_310804.html]</ref> In addition the [[Chemical Abstracts Service]] has devised a method to index chemical substances. In this scheme each chemical substance is identifiable by a number known as its [[CAS registry number]].
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| ====Molecule====
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| {{Main|Molecule}}
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| [[File:Caffeine (1) 3D ball.png|230px|thumb|right|A ball-and-stick representation of the [[caffeine]] molecule (C<sub>8</sub>H<sub>10</sub>N<sub>4</sub>O<sub>2</sub>).]]
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| A ''molecule'' is the smallest indivisible portion of a pure [[chemical substance]] that has its unique set of chemical properties, that is, its potential to undergo a certain set of chemical reactions with other substances. However, this definition only works well for substances that are composed of molecules, which is not true of many substances (see below). Molecules are typically a set of atoms bound together by [[covalent bond]]s, such that the structure is electrically neutral and all valence electrons are paired with other electrons either in bonds or in [[lone pair]]s.
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| Thus, molecules exist as electrically neutral units, unlike ions. When this rule is broken, giving the "molecule" a charge, the result is sometimes named a [[molecular ion]] or a polyatomic ion. However, the discrete and separate nature of the molecular concept usually requires that molecular ions be present only in well-separated form, such as a directed beam in a vacuum in a [[mass spectrometer]]. Charged polyatomic collections residing in solids (for example, common sulfate or nitrate ions) are generally not considered "molecules" in chemistry.
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| [[File:Benzene-2D-full.svg|thumb|150px|left|A 2-D [[skeletal model]] of a [[benzene]] molecule (C<sub>6</sub>H<sub>6</sub>)]]
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| The "inert" or [[Noble gas|noble gas elements]] ([[helium]], [[neon]], [[argon]], [[krypton]], [[xenon]] and [[radon]]) are composed of lone atoms as their smallest discrete unit, but the other isolated chemical elements consist of either molecules or networks of atoms bonded to each other in some way. Identifiable molecules compose familiar substances such as water, air, and many organic compounds like alcohol, sugar, gasoline, and the various [[pharmaceutical]]s.
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| However, not all substances or chemical compounds consist of discrete molecules, and indeed most of the solid substances that makes up the solid crust, mantle, and core of the Earth are chemical compounds without molecules. These other types of substances, such as [[ionic compounds]] and [[network solids]], are organized in such a way as to lack the existence of identifiable molecules ''per se''. Instead, these substances are discussed in terms of [[formula unit]]s or [[unit cell]]s as the smallest repeating structure within the substance. Examples of such substances are mineral salts (such as [[table salt]]), solids like carbon and diamond, metals, and familiar [[silica]] and [[silicate minerals]] such as quartz and granite.
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| One of the main characteristics of a molecule is its geometry often called its [[molecular structure|structure]]. While the structure of diatomic, triatomic or tetra atomic molecules may be trivial, (linear, angular pyramidal etc.) the structure of polyatomic molecules, that are constituted of more than six atoms (of several elements) can be crucial for its chemical nature.
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| ====Substance and mixture====
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| {{infobox
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| | data1 = [[File:Cín.png|100px]][[File:Sulfur-sample.jpg|100px]]
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| | data2 = [[File:Diamants maclés 2(République d'Afrique du Sud).jpg|100px]][[File:Sugar 2xmacro.jpg|100px]]
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| | data3 = [[File:Sal (close).jpg|100px]][[File:Sodium bicarbonate.jpg|100px]]
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| | data5 = Examples of pure chemical substances. From left to right: the elements [[tin]] (Sn) and [[sulfur]] (S), [[diamond]] (an [[allotrope]] of [[carbon]]), [[sucrose]] (pure sugar), and [[sodium chloride]] (salt) and [[sodium bicarbonate]] (baking soda), which are both ionic compounds.
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| }}
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| A chemical substance is a kind of matter with a definite [[chemical composition|composition]] and set of [[chemical properties|properties]].<ref>{{Cite book| title = General Chemistry | author = Hill, J.W.; Petrucci, R.H.; McCreary, T.W.; Perry, S.S. | edition = 4th | publisher = Pearson Prentice Hall | location = Upper Saddle River, NJ | year = 2005 | page = 37}}</ref> A collection of substances is called a mixture. Examples of mixtures are [[Earth's atmosphere|air]] and alloys.{{citation needed|date=September 2013}}
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| ====Mole and amount of substance====
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| {{Main|Mole (unit)|l1=Mole}}
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| The mole is a unit of measurement that denotes an [[amount of substance]] (also called chemical amount). The mole is defined as the number of atoms found in exactly 0.012 kilogram (or 12 grams) of [[carbon-12]], where the carbon-12 atoms are unbound, at rest and in their [[ground state]].<ref>{{cite web|url=http://www.bipm.org/en/si/base_units/ |title=Official SI Unit definitions |publisher=Bipm.org |date= |accessdate=2011-06-12}}</ref> The number of entities per mole is known as the [[Avogadro constant]], and is determined empirically to be approximately 6.022{{e|23}} mol<sup>−1</sup>.{{sfn|Burrows|Holman|Parsons|Pilling|2008|p=16}} [[Molar concentration]] is the amount of a particular substance per volume of [[solution]], and is commonly reported in mol[[decimetre|dm]]<sup>−3</sup>.{{sfn|Atkins|de Paula|2009|p=9}}
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| ===Phase===
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| [[File:Phase changes.svg|thumb|280px|Example of phase changes]]
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| {{Main|Phase (matter)|l1=Phase}}
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| In addition to the specific chemical properties that distinguish different chemical classifications chemicals can exist in several phases. For the most part, the chemical classifications are independent of these bulk phase classifications; however, some more exotic phases are incompatible with certain chemical properties. A ''phase'' is a set of states of a chemical system that have similar bulk structural properties, over a range of conditions, such as [[pressure]] or [[temperature]].
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| Physical properties, such as [[density]] and [[refractive index]] tend to fall within values characteristic of the phase. The phase of matter is defined by the ''[[phase transition]]'', which is when energy put into or taken out of the system goes into rearranging the structure of the system, instead of changing the bulk conditions.
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| Sometimes the distinction between phases can be continuous instead of having a discrete boundary, in this case the matter is considered to be in a [[supercritical fluid|supercritical]] state. When three states meet based on the conditions, it is known as a [[triple point]] and since this is invariant, it is a convenient way to define a set of conditions.
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| The most familiar examples of phases are [[solid]]s, [[liquid]]s, and [[gas]]es. Many substances exhibit multiple solid phases. For example, there are three phases of solid [[iron]] (alpha, gamma, and delta) that vary based on temperature and pressure. A principal difference between solid phases is the [[crystal structure]], or arrangement, of the atoms. Another phase commonly encountered in the study of chemistry is the ''aqueous'' phase, which is the state of substances dissolved in [[aqueous solution]] (that is, in water).
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| Less familiar phases include [[plasma physics|plasmas]], [[Bose-Einstein condensate]]s and [[fermionic condensate]]s and the [[paramagnetism|paramagnetic]] and [[ferromagnetism|ferromagnetic]] phases of [[magnet]]ic materials. While most familiar phases deal with three-dimensional systems, it is also possible to define analogs in two-dimensional systems, which has received attention for its relevance to systems in [[biology]].
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| ===Bonding===
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| {{Main|Chemical bond}}
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| [[File:Ionic bonding animation.gif|thumb|right|250px|An animation of the process of ionic bonding between [[sodium]] (Na) and [[chlorine]] (Cl) to form [[sodium chloride]], or common table salt. Ionic bonding involves one atom taking valence electrons from another (as opposed to sharing, which occurs in covalent bonding]]
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| Atoms sticking together in molecules or crystals are said to be bonded with one another. A chemical bond may be visualized as the [[multipole]] balance between the positive charges in the nuclei and the negative charges oscillating about them.<ref>{{cite web|author=Visionlearning |url=http://www.visionlearning.com/library/module_viewer.php?mid=55 |title=Chemical Bonding by Anthony Carpi, Ph |publisher=visionlearning |date= |accessdate=2011-06-12}}</ref> More than simple attraction and repulsion, the energies and distributions characterize the availability of an electron to bond to another atom.
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| A chemical bond can be a [[covalent bond]], an [[ionic bond]], a [[hydrogen bond]] or just because of [[Van der Waals force]]. Each of these kinds of bonds is ascribed to some potential. These potentials create the [[chemical interaction|interaction]]s which hold atoms together in [[molecule]]s or [[crystal]]s. In many simple compounds, [[Valence Bond Theory]], the Valence Shell Electron Pair Repulsion model ([[VSEPR]]), and the concept of [[oxidation number]] can be used to explain molecular structure and composition.
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| An ionic bond is formed when a metal loses one or more of its electrons, becoming a positively charged cation, and the electrons are then gained by the non-metal atom, becoming a negatively charged anion. The two oppositely charged ions attract one another, and the ionic bond is the electrostatic force of attraction between them. For example, [[sodium]] (Na), a metal, loses one electron to become an Na<sup>+</sup> cation while [[chlorine]] (Cl), a non-metal, gains this electron to become Cl<sup>-</sup>. The ions are held together due to electrostatic attraction, and that compound [[sodium chloride]] (NaCl), or common table salt, is formed.
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| [[File:Elektronenformel Punkte CH4.svg|thumb|160px|left|In the [[methane]] molecule (CH<sub>4</sub>), the carbon atom shares a pair of valence electrons with each of the four hydrogen atoms. Thus, the octet rule is satisfied for C-atom (it has eight electrons in its valence shell) and the duet rule is satisfied for the H-atoms (they have two electrons in their valence shells.]]
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| In a covalent bond, one or more pairs of [[valence electron]]s are shared by two atoms: the resulting electrically neutral group of bonded atoms is termed a [[molecule]]. Atoms will share valence electrons in such a way as to create a [[noble gas]] electron configuration (eight electrons in their outermost shell) for each atom. Atoms that tend to combine in such a way that they each have eight electrons in their valence shell are said to follow the [[octet rule]]. However, some elements like [[hydrogen]] and [[lithium]] need only two electron in their outermost shell to attain this stable configuration; these atoms are said to follow the ''duet rule'', and in this way they are reaching the electron configuration of the noble gas [[helium]], which has two electrons in its outer shell.
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| Similarly, theories from [[classical physics]] can be used to predict many ionic structures. With more complicated compounds, such as [[complex (chemistry)|metal complexes]], valence bond theory is less applicable and alternative approaches, such as the [[molecular orbital]] theory, are generally used. See diagram on electronic orbitals.
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| ===Energy===
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| {{Main|Energy}}
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| In the context of chemistry, energy is an attribute of a substance as a consequence of its [[atomic structure|atomic]], [[molecular structure|molecular]] or aggregate [[chemical structure|structure]]. Since a chemical transformation is accompanied by a change in one or more of these kinds of structures, it is invariably accompanied by an [[endothermic reaction|increase]] or [[exothermic reaction|decrease]] of [[energy]] of the substances involved. Some energy is transferred between the surroundings and the reactants of the reaction in the form of [[heat]] or [[photochemistry|light]]; thus the products of a reaction may have more or less energy than the reactants.
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| A reaction is said to be [[exergonic reaction|exergonic]] if the final state is lower on the energy scale than the initial state; in the case of [[endergonic reaction]]s the situation is the reverse. A reaction is said to be [[exothermic reaction|exothermic]] if the reaction releases heat to the surroundings; in the case of [[endothermic reaction]]s, the reaction absorbs heat from the surroundings.
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| Chemical reactions are invariably not possible unless the reactants surmount an energy barrier known as the [[activation energy]]. The ''speed'' of a chemical reaction (at given temperature T) is related to the activation energy E, by the Boltzmann's population factor <math>e^{-E/kT} </math> - that is the probability of a molecule to have energy greater than or equal to E at the given temperature T. This exponential dependence of a reaction rate on temperature is known as the [[Arrhenius equation]].
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| The activation energy necessary for a chemical reaction to occur can be in the form of heat, light, [[electricity]] or mechanical [[force]] in the form of [[ultrasound]].<ref>Reilly, Michael. (2007). [http://www.newscientisttech.com/article/dn11427 Mechanical force induces chemical reaction], NewScientist.com news service, Reilly {{Dead link|date=November 2010}}</ref>
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| A related concept [[thermodynamic free energy|free energy]], which also incorporates entropy considerations, is a very useful means for predicting the feasibility of a reaction and determining the state of equilibrium of a chemical reaction, in [[chemical thermodynamics]]. A reaction is feasible only if the total change in the [[Gibbs free energy]] is negative, <math> \Delta G \le 0 \,</math>; if it is equal to zero the chemical reaction is said to be at [[chemical equilibrium|equilibrium]].
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| There exist only limited possible states of energy for electrons, atoms and molecules. These are determined by the rules of [[quantum mechanics]], which require [[quantization (physics)|quantization]] of energy of a bound system. The atoms/molecules in a higher energy state are said to be excited. The molecules/atoms of substance in an excited energy state are often much more reactive; that is, more amenable to chemical reactions.
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| The phase of a substance is invariably determined by its energy and the energy of its surroundings. When the [[intermolecular force]]s of a substance are such that the energy of the surroundings is not sufficient to overcome them, it occurs in a more ordered phase like liquid or solid as is the case with water (H<sub>2</sub>O); a liquid at room temperature because its molecules are bound by [[hydrogen bonds]].<ref>[http://www.chem4kids.com/files/matter_changes.html Changing States of Matter] - Chemforkids.com</ref> Whereas [[hydrogen sulfide]] (H<sub>2</sub>S) is a gas at room temperature and standard pressure, as its molecules are bound by weaker [[dipole-dipole interaction]]s.
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| The transfer of energy from one chemical substance to another depends on the ''size'' of energy [[quantum|quanta]] emitted from one substance. However, heat energy is often transferred more easily from almost any substance to another because the [[phonons]] responsible for vibrational and rotational energy levels in a substance have much less energy than [[photons]] invoked for the electronic energy transfer. Thus, because vibrational and rotational energy levels are more closely spaced than electronic energy levels, heat is more easily transferred between substances relative to light or other forms of electronic energy. For example, ultraviolet electromagnetic radiation is not transferred with as much efficacy from one substance to another as thermal or electrical energy.
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| The existence of characteristic energy levels for different [[chemical substance]]s is useful for their identification by the analysis of [[spectral lines]]. Different kinds of spectra are often used in chemical [[spectroscopy]], e.g. [[infrared spectroscopy|IR]], [[microwave spectroscopy|microwave]], [[NMR]], [[electron spin resonance|ESR]], etc. Spectroscopy is also used to identify the composition of remote objects - like stars and distant galaxies - by analyzing their radiation spectra.
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| [[Image:Emission spectrum-Fe.svg|thumb|500px|center|Emission spectrum of [[iron]]]]
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| The term [[Energy#Chemical energy|chemical energy]] is often used to indicate the potential of a chemical substance to undergo a transformation through a [[chemical reaction]] or to transform other chemical substances.
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| ===Reaction===
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| {{Main|Chemical reaction}}
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| [[Image:VysokePece1.jpg|thumb|right|During chemical reactions, bonds between atoms break and form, resulting in different substances with different properties. In a blast furnace, iron oxide, a [[chemical compound|compound]], reacts with carbon monoxide to form iron, one of the [[chemical element]]s, and carbon dioxide.]]
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| When a chemical substance is transformed as a result of its interaction with another substance or with energy, a chemical reaction is said to have occurred. A ''chemical reaction'' is therefore a concept related to the 'reaction' of a substance when it comes in close contact with another, whether as a mixture or a [[solution]]; exposure to some form of energy, or both. It results in some energy exchange between the constituents of the reaction as well with the system environment which may be designed vessels which are often [[laboratory glassware]].
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| Chemical reactions can result in the formation or [[dissociation (chemistry)|dissociation]] of molecules, that is, molecules breaking apart to form two or more smaller molecules, or rearrangement of atoms within or across molecules. Chemical reactions usually involve the making or breaking of chemical bonds. [[Redox|Oxidation, reduction]], [[dissociation (chemistry)|dissociation]], acid-base [[neutralization (chemistry)|neutralization]] and molecular [[rearrangement reaction|rearrangement]] are some of the commonly used kinds of chemical reactions.
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| A chemical reaction can be symbolically depicted through a [[chemical equation]]. While in a non-nuclear chemical reaction the number and kind of atoms on both sides of the equation are equal, for a nuclear reaction this holds true only for the nuclear particles viz. protons and neutrons.<ref>[http://goldbook.iupac.org/C01034.html Chemical Reaction Equation]- IUPAC Goldbook</ref>
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| The sequence of steps in which the reorganization of chemical bonds may be taking place in the course of a chemical reaction is called its [[Reaction mechanism|mechanism]]. A chemical reaction can be envisioned to take place in a number of steps, each of which may have a different speed. Many [[reaction intermediates]] with variable stability can thus be envisaged during the course of a reaction. Reaction mechanisms are proposed to explain the [[chemical kinetics|kinetics]] and the relative product mix of a reaction. Many [[chemists|physical chemists]] specialize in exploring and proposing the mechanisms of various chemical reactions. Several empirical rules, like the [[Woodward-Hoffmann rules]] often come handy while proposing a mechanism for a chemical reaction.
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| According to the [[IUPAC]] gold book a chemical reaction is "a process that results in the interconversion of chemical species."<ref>[[Gold Book]] [http://goldbook.iupac.org/C01033.html Chemical Reaction] IUPAC Goldbook</ref> Accordingly, a chemical reaction may be an [[elementary reaction]] or a [[stepwise reaction]]. An additional caveat is made, in that this definition includes cases where the [[conformer|interconversion of conformers]] is experimentally observable. Such detectable chemical reactions normally involve sets of molecular entities as indicated by this definition, but it is often conceptually convenient to use the term also for changes involving single molecular entities (i.e. 'microscopic chemical events').
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| ===Ions and salts===
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| [[File:Potassium-chloride-3D-ionic.png|thumb|160px|The crystal lattice structure of [[potassium chloride]] (KCl), a salt which is formed due to the attraction of K<sup>+</sup> cations and Cl<sup>-</sup> anions. Note how the overall charge of the ionic compound is zero.]]
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| {{Main|Ion}}
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| An ''ion'' is a charged species, an atom or a molecule, that has lost or gained one or more electrons. When an atom loses an electron and thus has more protons than electrons, the atom is a positively-charged ion or [[cation]]. When an atom gains an electron and thus has more electrons than protons, the atom is a negatively-charged ion or [[anion]]. Cations and anions can form a crystalline lattice of neutral [[salt (chemistry)|salt]]s, such as the Na<sup>+</sup> and Cl<sup>-</sup> ions forming [[sodium chloride]], or NaCl. Examples of [[polyatomic ion]]s that do not split up during [[Acid-base reaction theories|acid-base reactions]] are [[hydroxide]] (OH<sup>−</sup>) and [[phosphate]] (PO<sub>4</sub><sup>3−</sup>).
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| [[plasma (physics)|Plasma]] is composed of gaseous matter that has been completely ionized, usually through high temperature.
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| ===Acidity and basicity===
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| [[File:Hydrogen-bromide-3D-vdW.png|thumb|left|160px|When [[hydrogen bromide]] (HBr), pictured, is dissolved in water, it forms the strong acid [[hydrobromic acid]]]]
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| {{Main|Acid–base reaction}}
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| A substance can often be classified as an acid or a [[base (chemistry)|base]]. There are several different theories which explain acid-base behavior. The simplest is [[Arrhenius acid|Arrhenius theory]], which states than an acid is a substance that produces [[hydronium ion]]s when it is dissolved in water, and a base is one that produces [[hydroxide ion]]s when dissolved in water. According to [[Brønsted–Lowry acid–base theory]], acids are substances that donate a positive [[hydrogen]] [[ion]] to another substance in a chemical reaction; by extension, a base is the substance which receives that hydrogen ion.
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| A third common theory is [[Lewis acids and bases|Lewis acid-base theory]], which is based on the formation of new chemical bonds. Lewis theory explains that an acid is a substance which is capable of accepting a pair of electrons from another substance during the process of bond formation, while a base is a substance which can provide a pair of electrons to form a new bond. According to this theory, the crucial things being exchanged are charges.<ref>{{cite web| url = http://www.apsidium.com/theory/lewis_acid.htm | title = The Lewis Acid-Base Concept | accessdate = 2010-07-31 | date = May 19, 2003 | work = Apsidium | archiveurl = //web.archive.org/web/20080527132328/http://www.apsidium.com/theory/lewis_acid.htm | archivedate = 2008-05-27}}</ref>{{Verify credibility|date=July 2010}}<!-- A nicely layed-out and informative page on Lewis; unfortunately the apsidium.com web site was anonymous and thus not "reliable source" --> There are several other ways in which a substance may be classified as an acid or a base, as is evident in the history of this concept <ref>{{cite web|url=http://www.bbc.co.uk/dna/h2g2/A708257 |title=History of Acidity |publisher=Bbc.co.uk |date=2004-05-27 |accessdate=2011-06-12}}</ref>
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| Acid strength is commonly measured by two methods. One measurement, based on the Arrhenius definition of acidity, is [[pH]], which is a measurement of the hydronium ion concentration in a solution, as expressed on a negative [[logarithm]]ic scale. Thus, solutions that have a low pH have a high hydronium ion concentration, and can be said to be more acidic. The other measurement, based on the Brønsted–Lowry definition, is the [[acid dissociation constant]] (K<sub>a</sub>), which measure the relative ability of a substance to act as an acid under the Brønsted–Lowry definition of an acid. That is, substances with a higher K<sub>a</sub> are more likely to donate hydrogen ions in chemical reactions than those with lower K<sub>a</sub> values.
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| ===Redox===
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| {{Main|Redox}}
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| Redox (''red''uction-''ox''idation) reactions include all [[chemical reaction]]s in which atoms have their [[oxidation state]] changed by either gaining electrons (reduction) or losing electrons (oxidation). Substances that have the ability to oxidize other substances are said to be oxidative and are known as [[oxidizing agents]], oxidants or oxidizers. An oxidant removes electrons from another substance. Similarly, substances that have the ability to reduce other substances are said to be reductive and are known as [[reducing agents]], reductants, or reducers.
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| A reductant transfers electrons to another substance, and is thus oxidized itself. And because it "donates" electrons it is also called an electron donor. Oxidation and reduction properly refer to a change in oxidation number—the actual transfer of electrons may never occur. Thus, oxidation is better defined as an increase in [[oxidation number]], and reduction as a decrease in oxidation number.
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| ===Equilibrium===
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| {{Main|Chemical equilibrium}}
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| Although the concept of [[Chemical equilibrium|equilibrium]] is widely used across sciences, in the context of chemistry, it arises whenever a number of different states of the chemical composition are possible. For example, in a mixture of several chemical compounds that can react with one another, or when a substance can be present in more than one kind of phase.
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| A system of chemical substances at equilibrium, even though having an unchanging composition, is most often not [[static equilibrium|static]]; molecules of the substances continue to react with one another thus giving rise to a [[dynamic equilibrium]]. Thus the concept describes the state in which the parameters such as chemical composition remain unchanged over time.
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| ===Chemical laws===
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| {{Main|Chemical law}}
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| Chemical reactions are governed by certain laws, which have become fundamental concepts in chemistry. Some of them are:
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| <div style="-moz-column-count:2; column-count:2;">
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| * [[Avogadro's law]]
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| * [[Beer-Lambert law]]
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| * [[Boyle's law]] (1662, relating pressure and volume)
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| * [[Charles's law]] (1787, relating volume and temperature)
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| * [[Fick's law of diffusion]]
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| * [[Gay-Lussac's law#Pressure-temperature law|Gay-Lussac's law]] (1809, relating pressure and temperature)
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| * [[Le Chatelier's Principle]]
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| * [[Henry's law]]
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| * [[Hess's Law]]
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| * [[Conservation of energy|Law of conservation of energy]] leads to the important concepts of [[Chemical equilibrium|equilibrium]], [[thermodynamics]], and [[chemical kinetics|kinetics]].
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| * [[Law of conservation of mass]] continues to be conserved in [[isolated system]]s, even in modern physics. However, [[special relativity]] shows that due to [[mass-energy equivalence]], whenever non-material "energy" (heat, light, kinetic energy) is removed from a non-isolated system, some mass will be lost with it. High energy losses result in loss of weighable amounts of mass, an important topic in [[nuclear chemistry]].
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| * [[Law of definite composition]], although in many systems (notably biomacromolecules and minerals) the ratios tend to require large numbers, and are frequently represented as a fraction.
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| * [[Law of multiple proportions]]
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| * [[Raoult's Law]]
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| </div>
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| ==Practice==
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| ===Subdisciplines===
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| Chemistry is typically divided into several major sub-disciplines. There are also several main cross-disciplinary and more specialized fields of chemistry.<ref>{{cite web|author=W.G. Laidlaw; D.E. Ryan And Gary Horlick; H.C. Clark, Josef Takats, And Martin Cowie; R.U. Lemieux |url=http://www.thecanadianencyclopedia.com/index.cfm?PgNm=TCE&Params=A1ARTA0001555 |title=Chemistry Subdisciplines |publisher=The Canadian Encyclopedia |date=1986-12-10 |accessdate=2011-06-12}}</ref>
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| * [[Analytical chemistry]] is the analysis of material samples to gain an understanding of their [[chemical composition]] and [[Chemical structure|structure]]. Analytical chemistry incorporates standardized experimental methods in chemistry. These methods may be used in all subdisciplines of chemistry, excluding purely theoretical chemistry.
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| * [[Biochemistry]] is the study of the [[chemical compound|chemicals]], [[chemical reaction]]s and [[chemical interaction]]s that take place in living [[organism]]s. Biochemistry and organic chemistry are closely related, as in [[medicinal chemistry]] or [[neurochemistry]]. Biochemistry is also associated with [[molecular biology]] and [[genetics]].
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| * [[Inorganic chemistry]] is the study of the properties and reactions of inorganic compounds. The distinction between organic and inorganic disciplines is not absolute and there is much overlap, most importantly in the sub-discipline of [[organometallic chemistry]].
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| * [[Materials science|Materials chemistry]] is the preparation, characterization, and understanding of substances with a useful function. The field is a new breadth of study in graduate programs, and it integrates elements from all classical areas of chemistry with a focus on fundamental issues that are unique to materials. Primary systems of study include the chemistry of condensed phases (solids, liquids, [[polymers]]) and [[interface (chemistry)|interfaces]] between different phases.
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| * [[Neurochemistry]] is the study of neurochemicals; including transmitters, peptides, proteins, lipids, sugars, and nucleic acids; their interactions, and the roles they play in forming, maintaining, and modifying the nervous system.
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| * [[Nuclear chemistry]] is the study of how subatomic particles come together and make nuclei. Modern [[Nuclear transmutation|Transmutation]] is a large component of nuclear chemistry, and the [[table of nuclides]] is an important result and tool for this field.
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| * [[Organic chemistry]] is the study of the structure, properties, composition, mechanisms, and [[chemical reaction|reactions]] of [[organic compound]]s. An organic compound is defined as any compound based on a carbon skeleton.
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| * [[Physical chemistry]] is the study of the physical and fundamental basis of chemical systems and processes. In particular, the energetics and dynamics of such systems and processes are of interest to physical chemists. Important areas of study include [[chemical thermodynamics]], [[chemical kinetics]], [[electrochemistry]], [[statistical mechanics]], [[spectroscopy]], and more recently, [[astrochemistry]].<ref>{{Cite journal| author = Herbst, Eric | title = Chemistry of Star-Forming Regions | journal = Journal of Physical Chemistry A | date = May 12, 2005 | volume = 109 | pages = 4017–4029 | issue = 18 | doi = 10.1021/jp050461c | pmid = 16833724}}</ref> Physical chemistry has large overlap with [[molecular physics]]. Physical chemistry involves the use of [[calculus|infinitesimal calculus]] in deriving equations. It is usually associated with [[quantum chemistry]] and theoretical chemistry. Physical chemistry is a distinct discipline from [[chemical physics]], but again, there is very strong overlap.
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| * [[Theoretical chemistry]] is the study of chemistry via fundamental theoretical reasoning (usually within [[mathematics]] or [[physics]]). In particular the application of [[quantum mechanics]] to chemistry is called [[quantum chemistry]]. Since the end of the [[World War II|Second World War]], the development of computers has allowed a systematic development of [[computational chemistry]], which is the art of developing and applying [[computer program]]s for solving chemical problems. Theoretical chemistry has large overlap with (theoretical and experimental) [[condensed matter physics]] and [[molecular physics]].
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| Other disciplines within chemistry are traditionally grouped by the type of matter being studied or the kind of study. These include [[inorganic chemistry]], the study of [[inorganic]] matter; [[organic chemistry]], the study of [[organic compound|organic]] (carbon based) matter; [[biochemistry]], the study of [[chemical substance|substances]] found in [[organisms|biological organisms]]; [[physical chemistry]], the study of chemical processes using physical concepts such as [[thermodynamics]] and [[quantum mechanics]]; and [[analytical chemistry]], the analysis of material samples to gain an understanding of their [[chemical composition]] and [[Chemical structure|structure]]. Many more specialized disciplines have emerged in recent years, e.g. [[neurochemistry]] the chemical study of the [[nervous system]] (see [[#Subdisciplines|subdisciplines]]).
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| Other fields include [[agrochemistry]], [[astrochemistry]] (and [[cosmochemistry]]), [[atmospheric chemistry]], [[chemical engineering]], [[chemical biology]], [[chemo-informatics]], [[electrochemistry]], [[environmental chemistry]], [[femtochemistry]], [[flavor|flavor chemistry]], [[flow chemistry]], [[geochemistry]], [[green chemistry]], [[histochemistry]], [[history of chemistry]], [[hydrogenation|hydrogenation chemistry]], [[immunochemistry]], [[marine chemistry]], [[materials science]], [[mathematical chemistry]], [[mechanochemistry]], [[medicinal chemistry]], [[molecular biology]], [[molecular mechanics]], [[nanotechnology]], [[natural product chemistry]], [[oenology]], [[organometallic chemistry]], [[petrochemistry]], [[pharmacology]], [[photochemistry]], [[physical organic chemistry]], [[phytochemistry]], [[polymer chemistry]], [[radiochemistry]], [[solid-state chemistry]], [[sonochemistry]], [[supramolecular chemistry]], [[surface chemistry]], [[synthetic chemistry]], [[thermochemistry]], and many others.
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| ===Chemical industry===
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| {{Main|Chemical industry}}
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| The [[chemical industry]] represents an important economic activity. The global top 50 chemical producers in 2004 had sales of 587 billion [[US dollars]] with a profit margin of 8.1% and [[research and development]] spending of 2.1% of total chemical sales.<ref>{{Cite journal| title = Top 50 Chemical Producers | journal = Chemical & Engineering News | date = July 18, 2005 | volume = 83 | issue = 29 | pages = 20–23 | url = http://pubs.acs.org/cen/coverstory/83/8329globaltop50.html}}</ref>
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| ===Professional societies===
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| {{div col|colwidth=20em}}
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| * [[American Chemical Society]]
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| * [[American Society for Neurochemistry]]
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| * [[Chemical Institute of Canada]]
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| * [[Chemical Society of Peru]]
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| * [[International Union of Pure and Applied Chemistry]]
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| * [[Royal Australian Chemical Institute]]
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| * [[Royal Netherlands Chemical Society]]
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| * [[Royal Society of Chemistry]]
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| * [[Society of Chemical Industry]]
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| * [[World Association of Theoretical and Computational Chemists]]
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| * [[List of chemistry societies]]
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| {{div col end}}
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| ==See also==
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| {{Wikipedia books|Chemistry}}
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| {{Portal|Chemistry|Science}}
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| {{Main|Outline of chemistry}}
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| * [[Glossary of chemistry terms]]
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| * [[Common chemicals]]
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| * [[International Year of Chemistry]]
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| * [[List of chemists]]
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| * [[List of compounds]]
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| * [[List of important publications in chemistry]]
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| * [[List of software for molecular mechanics modeling]]
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| * [[List of unsolved problems in chemistry]]
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| * [[Periodic Systems of Small Molecules]]
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| * [[Philosophy of chemistry]]
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| ==References==
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| {{Reflist|2}}
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| ==Bibliography==
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| *{{cite book |ref=harv |last1=Atkins |first1=Peter |authorlink1=Peter Atkins |last2=de Paula |first2=Julio |title=Elements of Physical Chemistry |edition=5th |year=2009 |origyear=1992 |publisher=[[Oxford University Press]] |location=New York |isbn=978-0-19-922672-6}}
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| *{{cite book |ref=harv |last1=Burrows |first1=Andrew |last2=Holman |first2=John |last3=Parsons |first3=Andrew |last4=Pilling |first4=Gwen |last5=Price |first5=Gareth |title=Chemistry<sup>3</sup> |year=2009 |publisher=[[Oxford University Press]] |location=Italy |isbn=978-0-19-927789-6}}
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| *{{cite book |ref=harv |last1=Housecroft |first1=Catherine E. |last2=Sharpe |first2=Alan G. |title=Inorganic Chemistry |edition=3rd |year=2008 |origyear=2001 |publisher=[[Pearson Education]] |location=Harlow, Essex |isbn=978-0-13-175553-6 |oclc= |zbl= |doi= |id=}}
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| ==Further reading==
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| {{Sister project links|Chemistry}}
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| {{wikiversity|chemistry|at-link=School:Chemistry|at=The School of Chemistry}}
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| ;Popular reading
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| * Atkins, P.W. ''Galileo's Finger'' ([[Oxford University Press]]) ISBN 0-19-860941-8
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| * Atkins, P.W. ''Atkins' Molecules'' (Cambridge University Press) ISBN 0-521-82397-8
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| * Kean, Sam. ''The Disappearing Spoon - and other true tales from the Periodic Table ''(Black Swan) London, 2010 ISBN 978-0-552-77750-6
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| * [[Primo Levi|Levi, Primo]] ''The Periodic Table'' (Penguin Books) [1975] translated from the Italian by Raymond Rosenthal (1984) ISBN 978-0-14-139944-7
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| * Stwertka, A. ''A Guide to the Elements'' (Oxford University Press) ISBN 0-19-515027-9
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| ;Introductory undergraduate text books
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| * Atkins, P.W., Overton, T., Rourke, J., Weller, M. and Armstrong, F. ''Shriver and Atkins inorganic chemistry'' (4th edition) 2006 (Oxford University Press) ISBN 0-19-926463-5
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| * Chang, Raymond. ''Chemistry'' 6th ed. Boston: James M. Smith, 1998. ISBN 0-07-115221-0.
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| * {{Clayden}}
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| * Voet and Voet ''Biochemistry'' (Wiley) ISBN 0-471-58651-X
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| ;Advanced undergraduate-level or graduate text books
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| * Atkins, P.W. ''Physical Chemistry'' (Oxford University Press) ISBN 0-19-879285-9
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| * Atkins, P.W. et al. ''Molecular Quantum Mechanics'' (Oxford University Press)
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| * McWeeny, R. ''Coulson's Valence'' (Oxford Science Publications) ISBN 0-19-855144-4
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| * Pauling, L. ''The Nature of the chemical bond'' (Cornell University Press) ISBN 0-8014-0333-2
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| * Pauling, L., and Wilson, E. B. ''Introduction to Quantum Mechanics with Applications to Chemistry'' (Dover Publications) ISBN 0-486-64871-0
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| * Smart and Moore ''Solid State Chemistry: An Introduction'' (Chapman and Hall) ISBN 0-412-40040-5
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| * Stephenson, G. ''Mathematical Methods for Science Students'' (Longman) ISBN 0-582-44416-0
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| {{Branches of chemistry}}
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| {{Natural science}}
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| [[Category:Chemistry| ]]
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| [[Category:Physical sciences| ]]
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| [[Category:Natural sciences]]
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| {{Link GA|sr}}
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| {{Link FA|fo}}
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| {{Link FA|sl}}
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| {{Link FA|zh-yue}}
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