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{{Short description|Scientific field of study}}
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'''Chemistry''' is the scientific study of the properties and behavior of [[matter]].<ref name = "brown2018">{{cite book | last1 = Brown| first1 = Theodore L. | last2=LeMay | first2=H. Eugene Jr. | last3 = Bursten | first3 =  Bruce E. | last4 = Murphey | first4 = Catherine J. |  last5 = Woodward | first5 = Patrick M. | last6 = Stoltzfus | first6 = Matthew W. | last7 = Lufaso | first7 = Michael W. | chapter = Introduction: Matter, energy, and measurement | title = Chemistry: The Central Science | publisher = Pearson | edition = 14th | date = 2018 | location = New York | pages = 46–85 | isbn = 978-0134414232}}</ref><ref name = "missy2020">{{cite book |url=https://uen.pressbooks.pub/introductorychemistry/ | last1 = Kofoed| first1 = Melissa | last2=Miller | first2=Shawn | title = Introductory Chemistry | publisher = UEN Pressbooks | edition =  | date = 2020| location = Utah State University | pages =  | isbn = }}</ref> It is a [[physical science]] within the [[natural science]]s that studies the [[chemical element]]s that make up matter and [[chemical compound|compounds]] made of [[atom]]s, [[molecule]]s and [[ion]]s: their composition, structure, properties, behavior and the changes they undergo during [[chemical reaction|reactions]] with other [[chemical substance|substances]].<ref name="definition">{{cite web |url=http://chemweb.ucc.ie/what_is_chemistry.htm |title=What is Chemistry? |publisher=Chemweb.ucc.ie |access-date=12 June 2011 |archive-date=3 October 2018 |archive-url=https://web.archive.org/web/20181003061822/http://chemweb.ucc.ie/what_is_chemistry.htm |url-status=dead }}</ref><ref>{{cite web |title=Definition of CHEMISTRY |url=https://www.merriam-webster.com/dictionary/chemistry |website=Merriam-Webster |access-date=24 August 2020 |language=en |archive-date=7 August 2020 |archive-url=https://web.archive.org/web/20200807005724/https://www.merriam-webster.com/dictionary/chemistry |url-status=live }}</ref><ref>{{cite web |title=Definition of chemistry {{!}} Dictionary.com |url=http://dictionary.reference.com/browse/Chemistry |website=www.dictionary.com |access-date=24 August 2020 |language=en |archive-date=5 March 2016 |archive-url=https://web.archive.org/web/20160305233029/http://dictionary.reference.com/browse/chemistry |url-status=live }}</ref><ref>{{Cite web|title=Chemistry Is Everywhere|url=https://www.acs.org/content/acs/en/education/whatischemistry/everywhere.html|website=[[American Chemical Society]]|access-date=1 December 2020|archive-date=29 November 2020|archive-url=https://web.archive.org/web/20201129190223/https://www.acs.org/content/acs/en/education/whatischemistry/everywhere.html|url-status=live}}</ref> Chemistry also addresses the nature of [[chemical bond]]s in [[chemical compound]]s.

In the scope of its subject, chemistry occupies an intermediate position between [[physics]] and [[biology]].<ref>Carsten Reinhardt. ''Chemical Sciences in the 20th Century: Bridging Boundaries''. Wiley-VCH, 2001. {{ISBN|3-527-30271-9}}. pp.&nbsp;1–2.</ref> It is sometimes called [[the central science]] because it provides a foundation for understanding both [[Basic research|basic]] and [[Applied science|applied]] scientific disciplines at a fundamental level.<ref>Theodore L. Brown, H. Eugene Lemay, Bruce Edward Bursten, H. Lemay. ''Chemistry: The Central Science''. Prentice Hall; 8 ed. (1999). {{ISBN|0-13-010310-1}}. pp.&nbsp;3–4.</ref> For example, chemistry explains aspects of plant growth ([[botany]]), the formation of igneous rocks ([[geology]]), how atmospheric ozone is formed and how environmental pollutants are degraded ([[ecology]]), the properties of the soil on the Moon ([[cosmochemistry]]), how medications work ([[pharmacology]]), and how to collect [[DNA]] evidence at a crime scene ([[forensic]]s).

Chemistry has existed under various names since ancient times.<ref>{{Cite web|url=https://www.britannica.com/science/chemistry/Chemistry-and-society|title=Chemistry – Chemistry and society |website=Britannica |access-date=6 May 2023|archive-date=6 May 2023|archive-url=https://web.archive.org/web/20230506122546/https://www.britannica.com/science/chemistry/Chemistry-and-society|url-status=live}}</ref> It has evolved, and now chemistry encompasses various areas of specialisation, or subdisciplines, that continue to increase in number and interrelate to create further interdisciplinary fields of study. The applications of various fields of chemistry are used frequently for economic purposes in the [[chemical industry]].

==Etymology==
{{Main|Etymology of chemistry}}

The word ''[[Chemistry (word)|chemistry]]'' comes from a modification during the [[Renaissance]] of the word ''[[alchemy]],'' which referred to an earlier set of practices that encompassed elements of chemistry, [[metallurgy]], [[philosophy]], [[astrology]], [[astronomy]], [[mysticism]], and [[medicine]]. Alchemy is often associated with the quest to turn lead or other base metals into gold, though [[alchemy|alchemists]] were also interested in many of the questions of modern chemistry.<ref>{{Cite book |last=Ihde |first=Aaron J. |title=The development of modern chemistry |date=1984 |publisher=Dover |isbn=978-0-486-64235-2 |location=New York}}</ref><ref>{{Cite journal |last=Newman |first=William R. |date=2011 |title=What Have We Learned from the Recent Historiography of Alchemy? |url=https://www.journals.uchicago.edu/doi/10.1086/660140 |journal=Isis |language=en |volume=102 |issue=2 |pages=313–321 |doi=10.1086/660140 |pmid=21874691 |issn=0021-1753}}</ref>

The modern word ''alchemy'' in turn is derived from the [[Arabic]] word {{transliteration|ar|al-kīmīā}} ({{lang|ar|الكیمیاء}}). This may have [[Egyptian language|Egyptian]] origins since {{transliteration|ar|al-kīmīā}} is derived from the [[Ancient Greek]] {{lang|grc|χημία}}, which is in turn derived from the word {{lang|egy|[[Name of Egypt|Kemet]]}}, which is the ancient name of Egypt in the Egyptian language.<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> Alternately, {{transliteration|ar|al-kīmīā}} may derive from {{lang|grc|χημεία}} 'cast together'.<ref>Weekley, Ernest (1967). Etymological Dictionary of Modern English. New York: Dover Publications. {{ISBN|0-486-21873-2}}.</ref>

==Modern principles==
[[File:Lab bench.jpg|thumb|upright=1.15|[[Laboratory]], Institute of Biochemistry, [[University of Cologne]] in [[Germany]] ]]

The current model of atomic structure is the [[quantum mechanical model]].<ref>{{cite encyclopedia|title=chemical bonding|url=https://www.britannica.com/EBchecked/topic/684121/chemical-bonding/43383/The-quantum-mechanical-model|encyclopedia=Britannica|publisher=Encyclopædia Britannica|access-date=1 November 2012|archive-date=26 April 2012|archive-url=https://web.archive.org/web/20120426054956/http://www.britannica.com/EBchecked/topic/684121/chemical-bonding/43383/The-quantum-mechanical-model|url-status=live}}</ref> Traditional chemistry starts with the study of [[elementary particle]]s, [[atom]]s, [[molecule]]s,<ref>Anthony Carpi. [https://www.visionlearning.com/library/module_viewer.php?mid=49 Matter: Atoms from Democritus to Dalton], {{Webarchive|url=https://web.archive.org/web/20070228203304/http://www.visionlearning.com/library/module_viewer.php?mid=49|date=28 February 2007}}.</ref> [[chemical substance|substances]], [[metal]]s, [[crystal]]s and other aggregates of [[matter]]. Matter can be studied in solid, liquid, gas and plasma [[states of matter|states]], in isolation or in combination. The interactions, [[chemical reaction|reactions]] and transformations that are studied in chemistry are usually the result of interactions between atoms, leading to rearrangements of the [[chemical bond]]s which hold atoms together. Such behaviors are studied in a chemistry [[laboratory]].

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.

[[File:Chemicals in flasks.jpg|thumb|right|Solutions of substances in reagent bottles, including [[ammonium hydroxide]] and [[nitric acid]], illuminated in different colors]]

A [[chemical reaction]] is a transformation of some substances into one or more different substances.<ref>IUPAC, [[Gold Book]] [http://goldbook.iupac.org/C01033.html Definition], {{Webarchive|url=https://web.archive.org/web/20070304035235/http://goldbook.iupac.org/C01033.html|date=4 March 2007}}.</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 the number of atoms on either side is unequal, the transformation is referred to as 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 law]]s.

[[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 [[chemist]]s.<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=29 October 1999 |access-date=12 June 2011 |archive-url=https://web.archive.org/web/20110610111332/http://www.calmis.ca.gov/file/occguide/CHEMIST.HTM |archive-date=10 June 2011 |url-status=dead }}</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 |access-date=12 June 2011 |archive-date=24 June 2011 |archive-url=https://web.archive.org/web/20110624140458/http://antoine.frostburg.edu/chem/senese/101/matter/ |url-status=live }}</ref>

===Matter===
{{Main|Matter}}
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>

====Atom====
{{Main|Atom}}
[[File:Atom Diagram.svg|thumb|upright=0.75|left|A diagram of an atom based on the [[Rutherford model]]]]

The [[atom]] is the basic unit of chemistry. It consists of a dense core called the [[atomic nucleus]] surrounded by a space occupied by an [[electron cloud]]. The nucleus is made up of positively charged [[proton]]s and uncharged [[neutron]]s (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 approximately 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|2009|p=13}}{{sfn|Housecroft|Sharpe|2008|p=2}}

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., [[metal]]lic, [[ion]]ic, [[covalent]]).

====Element====
[[File:Simple Periodic Table Chart-blocks.svg|thumb|right|upright=1.35|Standard form of the [[periodic table]] of chemical elements. The colors represent different [[block (periodic table)|blocks]] of elements.]]
{{Main|Chemical element}}

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}}

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}}

====Compound====
[[File:Carbon dioxide structure.png|thumb|left|upright=0.6|[[Carbon dioxide]] (CO<sub>2</sub>), an example of a chemical compound]]
{{Main|Chemical compound}}

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|2009|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 |access-date=12 June 2011 |archive-date=8 June 2011 |archive-url=https://web.archive.org/web/20110608140820/http://www.acdlabs.com/iupac/nomenclature/ |url-status=live }}</ref> The names for [[inorganic compound]]s are created according to the [[inorganic nomenclature]] system. When a compound has more than one component, then they are divided into two classes, the electropositive and the electronegative components.<ref name="IUPAC">{{cite book |last1=Connelly |first1=Neil G. |last2=Damhus |first2=Ture |last3=Hartshom |first3=Richard M. |last4=Hutton |first4=Alan T. |title=Nomenclature of Inorganic Chemistry IUPAC Recommendations 2005. |date=2005 |publisher=Royal Society of Chemistry Publishing / IUPAC |location=Cambridge |isbn=0854044388 |url=https://archive.org/details/nomenclatureinor2005conn |access-date=13 June 2022}}</ref> In addition the [[Chemical Abstracts Service|Chemical Abstracts Service (CAS)]] 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]].

====Molecule====
{{Main|Molecule}}
[[File:Caffeine (1) 3D ball.png|upright=1.05|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>)]]

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.

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. Some molecules contain one or more unpaired electrons, creating [[radical (chemistry)|radicals]]. Most radicals are comparatively reactive, but some, such as [[nitric oxide]] (NO) can be stable.

[[File:Benzene-2D-full.svg|thumb|upright=0.7|left|A 2-D [[structural formula]] of a [[benzene]] molecule (C<sub>6</sub>H<sub>6</sub>)]]
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.

However, not all substances or chemical compounds consist of discrete molecules, and indeed most of the solid substances that make up the solid crust, mantle, and core of the Earth are chemical compounds without molecules. These other types of substances, such as [[ionic compound]]s and [[Network covalent bonding|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 mineral]]s such as quartz and granite.

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 molecular geometry|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.

====Substance and mixture====
{{infobox
| data1 = [[File:Cín.png|100px]] [[File:Sulfur-sample.jpg|100px]]
| data2 = [[File:Diamants maclés 2(République d'Afrique du Sud).jpg|100px]] [[File:Sugar 2xmacro.jpg|100px]]
| data3 = [[File:Sal (close).jpg|100px]] [[File:Sodium bicarbonate.jpg|100px]]
| 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.
}}
A chemical substance is a kind of matter with a definite [[chemical composition|composition]] and set of [[chemical properties|properties]].<ref>{{Cite book |last1=Hill |first1=J. W. |title=General Chemistry |last2=Petrucci |first2=R. H. |last3=McCreary |first3=T. W. |last4=Perry |first4=S. S. |publisher=Pearson Prentice Hall |year=2005 |edition=4th |location=Upper Saddle River, New Jersey |page=37}}</ref> A collection of substances is called a mixture. Examples of mixtures are [[Earth's atmosphere|air]] and [[alloy]]s.<ref>{{cite book |last1=Avedesian |first1=M. M. |title=Magnesium and Magnesium Alloys |last2=Baker |first2=Hugh |publisher=ASM International |page=59}}</ref>

====Mole and amount of substance====
{{Main|Mole (unit)|l1=Mole}}
The mole is a unit of measurement that denotes an [[amount of substance]] (also called chemical amount). One mole is defined to contain exactly {{val|6.02214076|e=23}} particles (atoms, molecules, ions, or electrons), where the [[particle number|number of particles]] per mole is known as the [[Avogadro constant]].{{sfn|Burrows|Holman|Parsons|Pilling|2009|p=16}} [[Molar concentration]] is the amount of a particular substance per volume of [[solution (chemistry)|solution]], and is commonly reported in mol/[[decimetre|dm]]<sup>3</sup>.{{sfn|Atkins|de Paula|2009|p=9}}

===Phase===
[[File:Phase changes.svg|thumb|upright=1.25|Diagram showing relationships among the phases and the terms used to describe phase changes]]
{{Main|Phase (matter)|l1=Phase}}

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]].

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.

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.

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).

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]].

===Bonding===
{{Main|Chemical bond}}
[[File:Ionic bonding animation.gif|thumb|right|upright=1.15|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).]]

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= |title=Chemical Bonding by Anthony Carpi, PhD |url=http://www.visionlearning.com/library/module_viewer.php?mid=55 |url-status=live |archive-url=https://web.archive.org/web/20110717215216/http://www.visionlearning.com/library/module_viewer.php?mid=55 |archive-date=17 July 2011 |access-date=12 June 2011 |publisher=visionlearning}}</ref> More than simple attraction and repulsion, the energies and distributions characterize the availability of an electron to bond to another atom.

The 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 interactions 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.

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 [[Chloride|Cl<sup>−</sup>]]. The ions are held together due to electrostatic attraction, and that compound [[sodium chloride]] (NaCl), or common table salt, is formed.

[[File:Elektronenformel Punkte CH4.svg|thumb|upright=0.75|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).]]
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 electrons 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.

Similarly, theories from [[classical physics]] can be used to predict many ionic structures. With more complicated compounds, such as [[<!-- coordination complex or -->complex (chemistry)|metal complexes]], valence bond theory is less applicable and alternative approaches, such as the [[molecular orbital]] theory, are generally used.

===Energy===
{{Main|Energy}}

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.

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.

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]]. 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). [https://www.newscientist.com/article/dn11427-mechanical-force-induces-chemical-reaction.html Mechanical force induces chemical reaction], {{Webarchive|url=https://web.archive.org/web/20140814004108/http://www.newscientist.com/article/dn11427-mechanical-force-induces-chemical-reaction.html#.Uy6ySlendfA|date=14 August 2014}}, NewScientist.com news service.</ref>

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]].

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.

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], {{Webarchive|url=https://web.archive.org/web/20070428171905/http://www.chem4kids.com/files/matter_changes.html|date=28 April 2007}}, 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.

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 [[phonon]]s responsible for vibrational and rotational energy levels in a substance have much less energy than [[photon]]s 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.

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]], [[nuclear magnetic resonance|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.
[[File:Emission spectrum-Fe.svg|thumb|upright=2.2|Emission spectrum of [[iron]] ]]

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.

===Reaction===
{{Main|Chemical reaction}}
[[File: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.]]
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 (chemistry)|solution]]; exposure to some form of energy, or both. It results in some energy exchange between the constituents of the reaction as well as with the system environment, which may be designed vessels—often [[laboratory glassware]].

Chemical reactions can result in the formation or [[dissociation (chemistry)|dissociation]] of molecules, that is, molecules breaking apart to form two or more 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 examples of common chemical reactions.

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], {{Webarchive|url=https://web.archive.org/web/20071012013002/http://goldbook.iupac.org/C01034.html|date=12 October 2007}}, IUPAC Goldbook.</ref>

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 in handy while proposing a mechanism for a chemical reaction.

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], {{Webarchive|url=https://web.archive.org/web/20070304035235/http://goldbook.iupac.org/C01033.html|date=4 March 2007}}, 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 [[Conformational isomerism|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').

===Ions and salts===
[[File:Potassium-chloride-3D-ionic.png|thumb|upright=0.75|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. The overall charge of the ionic compound is zero.]]
{{Main|Ion}}

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)|salts]], 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]]s are [[hydroxide]] (OH<sup>−</sup>) and [[phosphate]] (PO<sub>4</sub><sup>3−</sup>).

[[plasma (physics)|Plasma]] is composed of gaseous matter that has been completely ionized, usually through high temperature.

===Acidity and basicity===
[[File:Hydrogen-bromide-3D-vdW.svg|thumb|left|upright=0.8|[[Hydrogen bromide]] exists in the gas phase as a diatomic molecule.]]
{{Main|Acid–base reaction}}

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 that 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.

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. 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=https://h2g2.com/edited_entry/A708257 |title=History of Acidity |publisher=BBC |date=27 May 2004 |access-date=12 June 2011 |archive-date=27 February 2009 |archive-url=https://web.archive.org/web/20090227024430/http://www.bbc.co.uk/dna/h2g2/A708257 |url-status=live }}</ref>

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 measures 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.

===Redox===
{{Main|Redox}}

Redox ({{not a typo|{{em|red}}uction}}-{{not a typo|{{em|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.

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.

===Equilibrium===
{{Main|Chemical equilibrium}}

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, as 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.

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.

===Chemical laws===
{{Main|Chemical law}}

Chemical reactions are governed by certain laws, which have become fundamental concepts in chemistry. Some of them are:
{{div col|colwidth=30em}}
* [[Avogadro's law]]
* [[Beer–Lambert law]]
* [[Boyle's law]] (1662, relating pressure and volume)
* [[Charles's law]] (1787, relating volume and temperature)
* [[Fick's laws of diffusion]]
* [[Pressure law|Gay-Lussac's law]] (1809, relating pressure and temperature)
* [[Le Chatelier's principle]]
* [[Henry's law]]
* [[Hess's law]]
* [[Conservation of energy|Law of conservation of energy]] leads to the important concepts of [[Chemical equilibrium|equilibrium]], [[thermodynamics]], and [[chemical kinetics|kinetics]].
* [[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]].
* [[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.
* [[Law of multiple proportions]]
* [[Raoult's law]]
{{div col end}}

==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}}
</ref>

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:Man Florence, Ashburnham 1166 fol 12r.jpg|left|thumb|250x250px|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]] and its 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.

==Practice==
In the practice of chemistry, '''pure chemistry''' is the study of the fundamental principles of chemistry, while '''applied chemistry''' applies that knowledge to develop technology and solve real-world problems.

===Subdisciplines===
{{see also|Outline of chemistry#Branches of chemistry}}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 |title=Chemistry Subdisciplines |url=https://www.thecanadianencyclopedia.ca/en/article/chemistry-subdisciplines |access-date=2024-04-01 |website=www.thecanadianencyclopedia.ca |language=en}}</ref>

* [[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.<ref>{{Cite web |title=Analytical Chemistry |url=https://www.acs.org/careers/chemical-sciences/areas/analytical-chemistry.html |access-date=2024-04-01 |website=American Chemical Society |language=en}}</ref>
[[File:DU640_spectrophotometer.jpg|thumb|upright=1.4|In analytical chemistry, [[spectroscopy]] studies interactions between electromagnetic radiation (light) and matter.<ref>{{Cite book |last1=Skoog |first1=Douglas A. |title=Principles of instrumental analysis |last2=Holler |first2=F. James |last3=Crouch |first3=Stanley R. |date=2018 |publisher=Cengage Learning |isbn=978-1-305-57721-3 |edition=7th |location=Australia |pages=120}}</ref> A [[Spectrophotometry|spectrophotometer]] is a machine used to measure the effect light has on matter. The model pictured is the Beckman DU-640]]
* [[Biochemistry]] is the study of the [[Chemical compound|chemicals]], [[chemical reaction]]s and interactions that take place at a molecular level in living [[organism]]s. Biochemistry is highly interdisciplinary, covering [[medicinal chemistry]], [[neurochemistry]], [[molecular biology]], [[Forensic science|forensics]], [[plant science]] and [[genetics]].<ref>{{Cite web |title=Studying Biochemistry |url=https://www.biochemistry.org/careers-and-education/studying-biochemistry/ |access-date=2024-04-11 |website=www.biochemistry.org |language=en}}</ref>
* [[Inorganic chemistry]] is the study of the properties and reactions of inorganic compounds, such as metals and minerals.<ref>{{Cite web |title=Inorganic Chemistry |url=https://www.acs.org/careers/chemical-sciences/areas/inorganic-chemistry.html |access-date=2024-04-01 |website=American Chemical Society |language=en}}</ref> The distinction between organic and inorganic disciplines is not absolute and there is much overlap, most importantly in the sub-discipline of [[organometallic chemistry]].
[[File:Metallocenes3.png|left|thumb|upright=1.6|The [[Kaminsky catalyst]] is an organometallic complex that features either [[zirconium]] or [[hafnium]] metal centers. Depending on the placement of the catalyst's [[cyclopentadiene]] [[ligand]]s, it can produce [[polypropylene]]s with different [[tacticity]].<ref>{{Cite journal |last=Kaminsky |first=Walter |date=1998-01-01 |title=Highly active metallocene catalysts for olefin polymerization |url=https://pubs.rsc.org/en/content/articlelanding/1998/dt/a800056e |journal=Journal of the Chemical Society, Dalton Transactions |language=en |issue=9 |pages=1413–1418 |doi=10.1039/A800056E |issn=1364-5447|url-access=subscription }}</ref> '''1''' creates atactic polypropylene, which is soft and [[Amorphous solid|amorphous]] with a free-flowing composition. '''2''' creates isotactic polypropylene, which is hard and used in re-usable plastic containers. '''3''' creates syndiotactic polypropylene, which is rubbery and semi-crystalline.<ref>{{Cite web |title=Polypropylene |url=https://pslc.ws/macrog/pp.htm |access-date=2024-04-11 |website=pslc.ws |language=en}}</ref>]]
* [[Materials Chemistry|Materials chemistry]] is the preparation, characterization, and understanding of solid state components or devices with a useful current or future function.<ref>{{Cite book |last=Fahlman |first=Bradley D. |title=Materials Chemistry |date=2011 |publisher=Springer Netherlands Springer e-books Imprint: Springer |isbn=978-94-007-0693-4 |edition=1st |location=Dordrecht |pages=1–4}}</ref> The field is a new breadth of study in graduate programs, and it integrates elements from all classical areas of chemistry like [[organic chemistry]], [[inorganic chemistry]], and [[crystallography]] with a focus on fundamental issues that are unique to [[material]]s. Primary systems of study include the chemistry of condensed phases (solids, liquids, [[polymers]]) and [[interface (matter)|interfaces]] between different phases.
* [[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.
* [[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. In addition to [[Nuclear medicine|medical applications]], nuclear chemistry encompasses [[nuclear engineering]] which explores the topic of using [[nuclear power]] sources for generating energy.<ref>{{Cite web |title=Nuclear Chemistry |url=https://www.acs.org/careers/chemical-sciences/fields/nuclear-chemistry.html |access-date=2024-04-11 |website=American Chemical Society |language=en}}</ref><ref>{{Cite web |date=2014-11-18 |title=21: Nuclear Chemistry |url=https://chem.libretexts.org/Bookshelves/General_Chemistry/Map%3A_Chemistry_-_The_Central_Science_(Brown_et_al.)/21%3A_Nuclear_Chemistry |access-date=2024-04-11 |website=Libretexts |language=en}}</ref>
[[File:Little Boy bomb.jpg|thumb|upright=1.4|The [[Little Boy]] is an [[Nuclear weapon|atomic bomb]] utilizing a [[uranium-235]] [[Nuclear fission|fission reaction]].<ref>{{Cite web |title=Little Boy and Fat Man – Nuclear Museum |url=https://ahf.nuclearmuseum.org/ahf/history/little-boy-and-fat-man/ |access-date=2024-04-11 |website=ahf.nuclearmuseum.org/ |language=en-US}}</ref> By firing sub-critical uranium into another mass of sub-critical uranium within the bomb, creating a [[supercritical mass]], a self-sustaining nuclear reaction starts. It generated an explosive force of over 15,000 tons of equivalent TNT.]]
* [[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. Organic compounds can be classified, organized and understood in reactions by their [[functional group]]s, unit atoms or molecules that show characteristic chemical properties in a compound.<ref>{{Cite book |last1=Brown |first1=William Henry |title=Organic chemistry |last2=Iverson |first2=Brent L. |last3=Anslyn |first3=Eric V. |last4=Foote |first4=Christopher S. |date=2018 |publisher=Cengage Learning |isbn=978-1-305-58035-0 |edition=8th |location=Boston, Massachusetts |pages=19}}</ref>
[[File:4-Hydroxybutanal.svg|thumb|upright=1.3|[[4-Hydroxybutanal]] is an [[organic compound]] with an [[aldehyde]] (right) functional group and an [[alcohol (chemistry)|alcohol]] (left) functional group.]]
* [[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]]. 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.
* [[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]].
[[File:Solvay_conference_1927.jpg|thumb|upright=1.6|The [[Solvay Conference|Solvay Conference of 1927]] featured foundational scientists to the field of theoretical chemistry and physics. This conference discussed [[electron]]s and [[photon]]s.]]

Other subdivisions include [[electrochemistry]], [[femtochemistry]], [[Flavoring|flavor chemistry]], [[flow chemistry]], [[immunohistochemistry]], [[hydrogenation|hydrogenation chemistry]], [[mathematical chemistry]], [[molecular mechanics]], [[natural product chemistry]], [[organometallic chemistry]], [[petrochemistry]], [[photochemistry]], [[physical organic chemistry]], [[polymer chemistry]], [[radiochemistry]], [[sonochemistry]], [[supramolecular chemistry]], [[synthetic chemistry]], and many others.

=== Interdisciplinary ===
[[Interdisciplinarity|Interdisciplinary]] fields include [[agrochemistry]], [[astrochemistry]] (and [[cosmochemistry]]), [[atmospheric chemistry]], [[chemical engineering]], [[chemical biology]], [[chemo-informatics]], [[environmental chemistry]], [[geochemistry]], [[green chemistry]], [[immunochemistry]], [[marine chemistry]], [[materials science]], [[mechanochemistry]], [[medicinal chemistry]], [[molecular biology]], [[nanotechnology]], [[oenology]], [[pharmacology]], [[phytochemistry]], [[solid-state chemistry]], [[surface science]], [[thermochemistry]], and many others.

===Industry===
{{Main|Chemical industry}}

The [[chemical industry]] represents an important economic activity worldwide. The [[List of largest chemical producers|global top 50 chemical producers]] in 2013 had sales of [[United States dollar|US$]]980.5 billion with a profit margin of 10.3%.<ref name="c&en2013">{{cite news |last=Tullo |first=Alexander H. |date=28 July 2014 |title=C&EN's Global Top 50 Chemical Firms For 2014 |url=https://cen.acs.org/articles/92/i30/CENs-Global-Top-50-Chemical.html |newspaper=Chemical & Engineering News |publisher=[[American Chemical Society]] |access-date=22 August 2014 |archive-date=26 August 2014 |archive-url=https://web.archive.org/web/20140826115133/http://cen.acs.org/articles/92/i30/CENs-Global-Top-50-Chemical.html |url-status=live }}</ref>

===Professional societies===
{{Main|List of chemistry societies}}
{{div col|colwidth=25em}}
* [[American Chemical Society]]
* [[American Society for Neurochemistry]]
* [[Chemical Institute of Canada]]
* [[Chemical Society of Peru]]
* [[International Union of Pure and Applied Chemistry]]
* [[Royal Australian Chemical Institute]]
* [[Royal Netherlands Chemical Society]]
* [[Royal Society of Chemistry]]
* [[Society of Chemical Industry]]
* [[World Association of Theoretical and Computational Chemists]]
{{div col end}}

==See also==
{{Portal|Chemistry|Science}}
{{div col|colwidth=30em}}
* [[Comparison of software for molecular mechanics modeling]]
* [[Glossary of chemistry terms]]
* [[International Year of Chemistry]]
* [[List of chemists]]
* [[List of compounds]]
* [[List of important publications in chemistry]]
* [[List of unsolved problems in chemistry]]
* [[Outline of chemistry]]
* [[Periodic systems of small molecules]]
* [[Philosophy of chemistry]]
* [[Science tourism]]
{{div col end}}

==References==
{{reflist}}

==Bibliography==
{{Refbegin}}
* {{cite book |last1=Atkins |first1=Peter |author-link1=Peter Atkins |last2=de Paula |first2=Julio |title=Elements of Physical Chemistry |edition=5th |year=2009 |orig-year=1992 |publisher=[[Oxford University Press]] |location=New York |isbn=978-0-19-922672-6}}
* {{cite book |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}}
* {{cite book |last1=Housecroft |first1=Catherine E. |last2=Sharpe |first2=Alan G. |title=Inorganic Chemistry |edition=3rd |year=2008 |orig-year=2001 |publisher=[[Pearson Education]] |location=Harlow, Essex |isbn=978-0-13-175553-6 }}
{{Refend}}

==Further reading==
'''Popular reading'''
* Atkins, P. W. ''Galileo's Finger'' ([[Oxford University Press]]) {{ISBN|0-19-860941-8}}
* Atkins, P. W. ''Atkins' Molecules'' (Cambridge University Press) {{ISBN|0-521-82397-8}}
* Kean, Sam. ''The Disappearing Spoon – and Other True Tales from the Periodic Table'' (Black Swan) London, England, 2010 {{ISBN|978-0-552-77750-6}}
* [[Primo Levi|Levi, Primo]] ''The Periodic Table'' (Penguin Books) [1975] translated from the Italian by Raymond Rosenthal (1984) {{ISBN|978-0-14-139944-7}}
* Stwertka, A. ''A Guide to the Elements'' (Oxford University Press) {{ISBN|0-19-515027-9}}
* {{cite web|title=Dictionary of the History of Ideas |url=http://etext.lib.virginia.edu/cgi-local/DHI/dhi.cgi?id=dv1-04 |url-status=dead |archive-url=https://web.archive.org/web/20080310214753/http://etext.lib.virginia.edu/cgi-local/DHI/dhi.cgi?id=dv1-04 |archive-date=10 March 2008 }}
* {{cite EB1911 |wstitle=Chemistry |volume=6 |pages=33–76|short=1}}

'''Introductory undergraduate textbooks'''
* Atkins, P.W., Overton, T., Rourke, J., Weller, M. and Armstrong, F. ''Shriver and Atkins Inorganic Chemistry'' (4th ed.) 2006 (Oxford University Press) {{ISBN|0-19-926463-5}}
* Chang, Raymond. ''Chemistry'' 6th ed. Boston, Massachusetts: James M. Smith, 1998. {{ISBN|0-07-115221-0}}
* {{Clayden}}
* Voet and Voet. ''Biochemistry'' (Wiley) {{ISBN|0-471-58651-X}}

'''Advanced undergraduate-level or graduate textbooks'''

* Atkins, P. W. ''Physical Chemistry'' (Oxford University Press) {{ISBN|0-19-879285-9}}
* Atkins, P. W. et al. ''Molecular Quantum Mechanics'' (Oxford University Press)
* McWeeny, R. ''Coulson's Valence'' (Oxford Science Publications) {{ISBN|0-19-855144-4}}
* Pauling, L. ''The Nature of the chemical bond'' (Cornell University Press) {{ISBN|0-8014-0333-2}}
* Pauling, L., and Wilson, E. B. ''Introduction to Quantum Mechanics with Applications to Chemistry'' (Dover Publications) {{ISBN|0-486-64871-0}}
* Smart and Moore. ''Solid State Chemistry: An Introduction'' (Chapman and Hall) {{ISBN|0-412-40040-5}}
* Stephenson, G. ''Mathematical Methods for Science Students'' (Longman) {{ISBN|0-582-44416-0}}

==External links==
{{Sister project links|v=no|Chemistry}}
* [http://www.saylor.org/site/textbooks/General%20Chemistry%20Principles,%20Patterns,%20and%20Applications.pdf General Chemistry principles, patterns and applications].
{{Branches of chemistry}}
{{Natural science}}

{{Authority control}}

[[Category:Chemistry| ]]