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'''Chemistry''' (from [[Egyptian language|Egyptian]] ''kēme'' (chem), meaning [[Classical element|"earth"]] '''See:''' [[Chemistry (etymology)]] for possible origins of this word. is the [[science]] concerned with  the composition, structure, and properties of [[matter]], as well as the changes it undergoes during [[chemical reaction]]s. [http://dictionary.reference.com/browse/Chemistry Chemistry]. (n.d.). Merriam-Webster's Medical Dictionary. Retrieved [[August 19]], [[2007]].  Chemistry is a [[physical science]] related to studies of various [[atom]]s, [[molecule]]s, [[crystal]]s and other  aggregates of matter whether in isolation or combination, which incorporates the concepts of [[energy]] and [[entropy]] in relation to the [[spontaneous reaction|spontaneity]] of [[chemical process]]es.

'''Chemistry''' (from [[Egyptian language|Egyptian]] ''kēme'' (chem), meaning [[Classical element|"earth"]] '''See:''' [[Chemistry (etymology)]] for possible origins of this word. is the [[science]] concerned with  the composition, structure, and properties of [[matter]], as well as the changes it undergoes during [[chemical reaction]]s. [https://dictionary.reference.com/browse/Chemistry Chemistry]. (n.d.). Merriam-Webster's Medical Dictionary. Retrieved [[August 19]], [[2007]].  Chemistry is a [[physical science]] related to studies of various [[atom]]s, [[molecule]]s, [[crystal]]s and other  aggregates of matter whether in isolation or combination, which incorporates the concepts of [[energy]] and [[entropy]] in relation to the [[spontaneous reaction|spontaneity]] of [[chemical process]]es.

==Overview==

==Overview==

Chemistry is the scientific study of interaction of substances called [[chemical substance]]s [http://chemweb.ucc.ie/what_is_chemistry.htm What is Chemistry?]  that are constituted of [[atom]]s or the subatomic components that make up atoms: [[proton]]s, [[electron]]s and [[neutron]]s.<ref>[http://www.visionlearning.com/library/module_viewer.php?mid=49 Matter: Atoms from Democritus to Dalton] by Anthony Carpi, Ph.D.</ref> Atoms combine to produce [[ion]]s, [[molecule]]s or [[crystal]]s. Chemistry can be called "[[the central science]]" because it connects the other [[natural science]]s, such as [[astronomy]], [[physics]], [[material science]], [[biology]], and [[geology]].<ref>Theodore L. Brown, H. Eugene Lemay, Bruce Edward Bursten, H. Lemay. ''Chemistry: The Central Science''. Prentice Hall; 8 edition (1999). ISBN 0130103101. Pages 3-4. It is sometimes called the central science because it 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 3527302719. Pages 1-2.

Chemistry is the scientific study of interaction of substances called [[chemical substance]]s [https://chemweb.ucc.ie/what_is_chemistry.htm What is Chemistry?]  that are constituted of [[atom]]s or the subatomic components that make up atoms: [[proton]]s, [[electron]]s and [[neutron]]s.<ref>[https://www.visionlearning.com/library/module_viewer.php?mid=49 Matter: Atoms from Democritus to Dalton] by Anthony Carpi, Ph.D.</ref> Atoms combine to produce [[ion]]s, [[molecule]]s or [[crystal]]s. Chemistry can be called "[[the central science]]" because it connects the other [[natural science]]s, such as [[astronomy]], [[physics]], [[material science]], [[biology]], and [[geology]].<ref>Theodore L. Brown, H. Eugene Lemay, Bruce Edward Bursten, H. Lemay. ''Chemistry: The Central Science''. Prentice Hall; 8 edition (1999). ISBN 0130103101. Pages 3-4. It is sometimes called the central science because it 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 3527302719. Pages 1-2.

The genesis 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. Dictionary of the History of Ideas: Alchemy [http://etext.lib.virginia.edu/cgi-local/DHI/dhi.cgi?id=dv1-04]

The genesis 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. Dictionary of the History of Ideas: Alchemy [https://etext.lib.virginia.edu/cgi-local/DHI/dhi.cgi?id=dv1-04]

The structure of objects we commonly use and the properties of the matter we commonly interact with, are a consequence of the properties of chemical substances and their interactions. For example, [[steel]] is [[Hardness (materials science)|harder]] than iron because its atoms are bound together in a more rigid [[crystalline lattice]]; wood burns or undergoes rapid [[oxidation]] because it can react spontaneously with [[oxygen]] in a [[chemical reaction]] above a certain [[temperature]]; sugar and salt dissolve in water because their molecular/ionic properties are such that dissolution is preferred under the ambient conditions.  

The structure of objects we commonly use and the properties of the matter we commonly interact with, are a consequence of the properties of chemical substances and their interactions. For example, [[steel]] is [[Hardness (materials science)|harder]] than iron because its atoms are bound together in a more rigid [[crystalline lattice]]; wood burns or undergoes rapid [[oxidation]] because it can react spontaneously with [[oxygen]] in a [[chemical reaction]] above a certain [[temperature]]; sugar and salt dissolve in water because their molecular/ionic properties are such that dissolution is preferred under the ambient conditions.  

The transformations that are studied in chemistry are a result of interaction either between different chemical substances or between [[matter]] and [[energy]]. Traditional chemistry involves study of [[interactions]] between [[chemical substance|substances]] in a chemistry [[laboratory]] using various forms of [[laboratory glassware]].  A [[chemical reaction]] is a transformation of some such substances into one or more other such substances.<ref>IUPAC [[Gold Book]] [http://www.iupac.org/goldbook/C01033.pdf Definition]  It can be symbolically depicted through a [[chemical equation]].  The number of atoms on the left and the right in the equation for a chemical transformation is most often equal. The nature 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.

The transformations that are studied in chemistry are a result of interaction either between different chemical substances or between [[matter]] and [[energy]]. Traditional chemistry involves study of [[interactions]] between [[chemical substance|substances]] in a chemistry [[laboratory]] using various forms of [[laboratory glassware]].  A [[chemical reaction]] is a transformation of some such substances into one or more other such substances.<ref>IUPAC [[Gold Book]] [https://www.iupac.org/goldbook/C01033.pdf Definition]  It can be symbolically depicted through a [[chemical equation]].  The number of atoms on the left and the right in the equation for a chemical transformation is most often equal. The nature 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.

[[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 analysed using the tools of [[chemical analysis]], e.g. [[spectroscopy]] and [[chromatography]].  

[[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 analysed using the tools of [[chemical analysis]], e.g. [[spectroscopy]] and [[chromatography]].  

Chemistry is an integral part of the [[science]] curriculum both at the [[high school]] as well as the early college level. At these levels, it is often called 'general chemistry' which is an introduction to a wide variety of fundamental concepts that enable the student to acquire tools and skills useful at the advanced levels, whereby chemistry is invariably studied in any of its various sub-disciplines. [[Scientists]], engaged in  chemical [[research]] are known as [[chemists]].[http://www.calmis.ca.gov/file/occguide/CHEMIST.HTM] Most chemists specialize in one or more sub-disciplines.

Chemistry is an integral part of the [[science]] curriculum both at the [[high school]] as well as the early college level. At these levels, it is often called 'general chemistry' which is an introduction to a wide variety of fundamental concepts that enable the student to acquire tools and skills useful at the advanced levels, whereby chemistry is invariably studied in any of its various sub-disciplines. [[Scientists]], engaged in  chemical [[research]] are known as [[chemists]].[https://www.calmis.ca.gov/file/occguide/CHEMIST.HTM] Most chemists specialize in one or more sub-disciplines.

==History==

==History==

The genesis of chemistry can be traced to the widely observed phenomenon of burning that led to [[metallurgy]]- the art and science of processing ores to get metals (e.g. [[History of metallurgy in the Indian subcontinent|metallurgy in ancient India]]). The greed for gold led to the discovery of the process for its purification, even though, the underlying principles were not well understood -- it was thought to be a transformation rather than purification. Many scholars in those days thought it reasonable to believe that there exist means for transforming cheaper (base) metals into gold. This gave way to alchemy, and the search for the [[Philosopher's Stone]], which was believed to bring about such a transformation by mere touch.[http://www.chemheritage.org/explore/ancients-time.html Alchemy Timeline]

The genesis of chemistry can be traced to the widely observed phenomenon of burning that led to [[metallurgy]]- the art and science of processing ores to get metals (e.g. [[History of metallurgy in the Indian subcontinent|metallurgy in ancient India]]). The greed for gold led to the discovery of the process for its purification, even though, the underlying principles were not well understood -- it was thought to be a transformation rather than purification. Many scholars in those days thought it reasonable to believe that there exist means for transforming cheaper (base) metals into gold. This gave way to alchemy, and the search for the [[Philosopher's Stone]], which was believed to bring about such a transformation by mere touch.[https://www.chemheritage.org/explore/ancients-time.html Alchemy Timeline]

Some consider [[Alchemy (Islam)|medieval Muslims]] to be the earliest chemists, who introduced precise [[observation]] and controlled [[experiment]]ation into the field, and discovered numerous [[chemical substance]]s. [[Will Durant]] (1980), ''The Age of Faith (The Story of Civilization, Volume 4)'', p. 162-186, Simon & Schuster, ISBN 0671012002:

Some consider [[Alchemy (Islam)|medieval Muslims]] to be the earliest chemists, who introduced precise [[observation]] and controlled [[experiment]]ation into the field, and discovered numerous [[chemical substance]]s. [[Will Durant]] (1980), ''The Age of Faith (The Story of Civilization, Volume 4)'', p. 162-186, Simon & Schuster, ISBN 0671012002:

The emergence of chemistry in Europe was primarily due to the recurrent incidence of the [[Bubonic plague|plague]] and blights there during the so called [[Dark Ages]]. This gave rise to a need for medicines. It was thought that there exists a universal medicine called the [[Elixir of Life]] that can cure all diseases, but like the Philosopher's Stone, it was never found.  

The emergence of chemistry in Europe was primarily due to the recurrent incidence of the [[Bubonic plague|plague]] and blights there during the so called [[Dark Ages]]. This gave rise to a need for medicines. It was thought that there exists a universal medicine called the [[Elixir of Life]] that can cure all diseases, but like the Philosopher's Stone, it was never found.  

For some practitioners, alchemy was an intellectual pursuit, over time, they got better at it. [[Paracelsus]] (1493-1541), for example, rejected the 4-elemental theory and with only a vague understanding of his chemicals and medicines, formed a hybrid of alchemy and science in what was to be called  ''[[iatrochemistry]]''. Similarly, the influences of philosophers such as [[Sir Francis Bacon]] (1561-1626) and [[René Descartes]] (1596-1650), who demanded more rigor in mathematics and in removing bias from scientific observations, led to a [[scientific revolution]]. In chemistry, this began with [[Robert Boyle]] (1627-1691), who came up with an equations known as the [[Boyle's Law]] about the characteristics of gaseous state. [http://www.bbc.co.uk/history/historic_figures/boyle_robert.shtml BBC - History - Robert Boyle (1627 - 1691)]  Chemistry indeed came of age when [[Antoine Lavoisier]] (1743-1794), developed the theory of [[Conservation of mass]] in 1783; and the development of the [[Atomic Theory]] by [[John Dalton]] around 1800.  The Law of Conservation of Mass resulted in the reformulation of chemistry based on this law and the oxygen theory of combustion, which was largely based on the work of Lavoisier.  Lavoisier's fundamental contributions to chemistry were a result of a conscious effort to fit all experiments into the framework of a single theory. He established the consistent use of the chemical balance, used oxygen to overthrow the [[phlogiston theory]], and developed a new system of chemical nomenclature and made contribution to the modern metric system.  Lavoisier  also worked to translate the archaic and technical language of chemistry into something that could be easily understood by the largely uneducated masses, leading to an increased public interest in chemistry. All these advances in chemistry led to what is usually called the [[chemical revolution]].  The contributions of Lavoisier led to what is now called modern chemistry - the chemistry that is studied in educational institutions all over the world.  It is because of these and other contributions that [[Antoine Lavoisier]] is often celebrated as the "[[Father of Modern Chemistry]]".  The later discovery of [[Friedrich Wöhler]] that many natural substances, [[organic compound]]s, can indeed be synthesized in a chemistry [[laboratory]] also helped the modern chemistry to mature from its infancy.

For some practitioners, alchemy was an intellectual pursuit, over time, they got better at it. [[Paracelsus]] (1493-1541), for example, rejected the 4-elemental theory and with only a vague understanding of his chemicals and medicines, formed a hybrid of alchemy and science in what was to be called  ''[[iatrochemistry]]''. Similarly, the influences of philosophers such as [[Sir Francis Bacon]] (1561-1626) and [[René Descartes]] (1596-1650), who demanded more rigor in mathematics and in removing bias from scientific observations, led to a [[scientific revolution]]. In chemistry, this began with [[Robert Boyle]] (1627-1691), who came up with an equations known as the [[Boyle's Law]] about the characteristics of gaseous state. [https://www.bbc.co.uk/history/historic_figures/boyle_robert.shtml BBC - History - Robert Boyle (1627 - 1691)]  Chemistry indeed came of age when [[Antoine Lavoisier]] (1743-1794), developed the theory of [[Conservation of mass]] in 1783; and the development of the [[Atomic Theory]] by [[John Dalton]] around 1800.  The Law of Conservation of Mass resulted in the reformulation of chemistry based on this law and the oxygen theory of combustion, which was largely based on the work of Lavoisier.  Lavoisier's fundamental contributions to chemistry were a result of a conscious effort to fit all experiments into the framework of a single theory. He established the consistent use of the chemical balance, used oxygen to overthrow the [[phlogiston theory]], and developed a new system of chemical nomenclature and made contribution to the modern metric system.  Lavoisier  also worked to translate the archaic and technical language of chemistry into something that could be easily understood by the largely uneducated masses, leading to an increased public interest in chemistry. All these advances in chemistry led to what is usually called the [[chemical revolution]].  The contributions of Lavoisier led to what is now called modern chemistry - the chemistry that is studied in educational institutions all over the world.  It is because of these and other contributions that [[Antoine Lavoisier]] is often celebrated as the "[[Father of Modern Chemistry]]".  The later discovery of [[Friedrich Wöhler]] that many natural substances, [[organic compound]]s, can indeed be synthesized in a chemistry [[laboratory]] also helped the modern chemistry to mature from its infancy.

The [[discoveries of the chemical elements]] has a long history from the days of alchemy and culminating in the creation of the [[periodic table]] of the chemical elements by [[Dmitri Mendeleev]] (1834-1907) [http://chemistry.about.com/library/weekly/aa030303a.htm Timeline of Element Discovery] and later discoveries of some [[synthetic elements]].

The [[discoveries of the chemical elements]] has a long history from the days of alchemy and culminating in the creation of the [[periodic table]] of the chemical elements by [[Dmitri Mendeleev]] (1834-1907) [https://chemistry.about.com/library/weekly/aa030303a.htm Timeline of Element Discovery] and later discoveries of some [[synthetic elements]].

==Etymology==

==Etymology==

The word ''chemistry'' comes from the earlier study of alchemy, which is basically the quest to make gold from earthen starting materials.<ref>Alchemy Lab: History of Alchemy [http://www.alchemylab.com/history_of_alchemy.htm]</ref> As to the origin of the word "alchemy" the question is a debatable one; it certainly can be traced back to the Greeks, and some, following E. Wallis Budge, have also asserted [[Ancient Egypt|Egyptian]] origins. Alchemy, generally, derives from the old French ''alkemie'' from the Arabic ''al-kimia'' - "the art of transformation". The Arabs borrowed the word "kimia" from the Greeks when they conquered [[Alexandria]] in the year 642 AD. A tentative outline is as follows:

The word ''chemistry'' comes from the earlier study of alchemy, which is basically the quest to make gold from earthen starting materials.<ref>Alchemy Lab: History of Alchemy [https://www.alchemylab.com/history_of_alchemy.htm]</ref> As to the origin of the word "alchemy" the question is a debatable one; it certainly can be traced back to the Greeks, and some, following E. Wallis Budge, have also asserted [[Ancient Egypt|Egyptian]] origins. Alchemy, generally, derives from the old French ''alkemie'' from the Arabic ''al-kimia'' - "the art of transformation". The Arabs borrowed the word "kimia" from the Greeks when they conquered [[Alexandria]] in the year 642 AD. A tentative outline is as follows:

#Egyptian alchemy [5,000 BCE - 400 BCE], formulate early "element" theories such as the [[Ogdoad]].

#Egyptian alchemy [5,000 BCE - 400 BCE], formulate early "element" theories such as the [[Ogdoad]].

==Basic concepts==

==Basic concepts==

Several [[concepts]] are essential for the study of chemistry, some of them are:[http://antoine.frostburg.edu/chem/senese/101/matter/]  

Several [[concepts]] are essential for the study of chemistry, some of them are:[https://antoine.frostburg.edu/chem/senese/101/matter/]  

===Atom===

===Atom===

A chemical substance is a kind of matter with a definite [[chemical composition|composition]] and set of [[chemical properties|properties]]. Strictly speaking, a mixture of compounds, elements or compounds and elements is not a chemical substance, but it may be called a chemical. Most of the substances we encounter in our daily life are some kind of mixture, e.g. [[Earth's atmosphere|air]], [[alloy]]s, [[biomass]] etc.

A chemical substance is a kind of matter with a definite [[chemical composition|composition]] and set of [[chemical properties|properties]]. Strictly speaking, a mixture of compounds, elements or compounds and elements is not a chemical substance, but it may be called a chemical. Most of the substances we encounter in our daily life are some kind of mixture, e.g. [[Earth's atmosphere|air]], [[alloy]]s, [[biomass]] etc.

Nomenclature of substances is a critical part of the language of chemistry. Generally it refers to a system for naming [[chemical compound]]s. Earlier in the history of chemistry substances were given name by their discoverer, which often led to some confusion and difficulty. However, today the IUPAC system of chemical nomenclature  allows chemists to specify by name specific compounds amongst the infinite variety of possible chemicals. The standard nomenclature of chemical substances is set by the [[International Union of Pure and Applied Chemistry]] (IUPAC). There are well-defined systems in place for naming chemical species.  [[Organic compound]]s are named according to the [[organic nomenclature]] system. IUPAC Nomenclature of Organic Chemistry [http://www.acdlabs.com/iupac/nomenclature/] [[Inorganic compound]]s are named according to the [[inorganic nomenclature]] system. IUPAC Provisional Recommendations for the Nomenclature of Inorganic Chemistry (2004) [http://www.iupac.org/reports/provisional/abstract04/connelly_310804.html] In addition the [[Chemical Abstracts Service]] has devised a method to index chemical substance. In this scheme each chemical substance is identifiable by a numeric number known as [[CAS registry number]].

Nomenclature of substances is a critical part of the language of chemistry. Generally it refers to a system for naming [[chemical compound]]s. Earlier in the history of chemistry substances were given name by their discoverer, which often led to some confusion and difficulty. However, today the IUPAC system of chemical nomenclature  allows chemists to specify by name specific compounds amongst the infinite variety of possible chemicals. The standard nomenclature of chemical substances is set by the [[International Union of Pure and Applied Chemistry]] (IUPAC). There are well-defined systems in place for naming chemical species.  [[Organic compound]]s are named according to the [[organic nomenclature]] system. IUPAC Nomenclature of Organic Chemistry [https://www.acdlabs.com/iupac/nomenclature/] [[Inorganic compound]]s are named according to the [[inorganic nomenclature]] system. IUPAC Provisional Recommendations for the Nomenclature of Inorganic Chemistry (2004) [https://www.iupac.org/reports/provisional/abstract04/connelly_310804.html] In addition the [[Chemical Abstracts Service]] has devised a method to index chemical substance. In this scheme each chemical substance is identifiable by a numeric number known as [[CAS registry number]].

===Molecule===

===Molecule===

===Mole===

===Mole===

A mole is the amount of a  [[Chemical substance|substance]] that contains as many elementary entities (atoms, molecules or ions) as there are atoms in 0.012 [[kilogram]] (or 12 [[gram]]s) of [[carbon-12]], where the carbon-12 atoms are unbound, at rest and in their [[ground state]]. [http://www.bipm.org/en/si/base_units/ Official SI Unit definitions] This number is known as the [[Avogadro constant]], and is determined empirically. The currently accepted value is 6.02214179(30){{e|23}} mol^-1 (2007 [[CODATA]]). It is much like the term "a [[dozen]]" in that it is an absolute number (having no units) and can describe any type of elementary object, although the mole's use is usually limited to measurement of [[subatomic]], [[atom]]ic, and [[molecule|molecular]] structures.

A mole is the amount of a  [[Chemical substance|substance]] that contains as many elementary entities (atoms, molecules or ions) as there are atoms in 0.012 [[kilogram]] (or 12 [[gram]]s) of [[carbon-12]], where the carbon-12 atoms are unbound, at rest and in their [[ground state]]. [https://www.bipm.org/en/si/base_units/ Official SI Unit definitions] This number is known as the [[Avogadro constant]], and is determined empirically. The currently accepted value is 6.02214179(30){{e|23}} mol^-1 (2007 [[CODATA]]). It is much like the term "a [[dozen]]" in that it is an absolute number (having no units) and can describe any type of elementary object, although the mole's use is usually limited to measurement of [[subatomic]], [[atom]]ic, and [[molecule|molecular]] structures.

The number of moles of a substance in one liter of a [[solution]] is known as its [[molarity]]. Molarity is the common unit used to express the [[concentration]] of a solution in [[physical chemistry]].

The number of moles of a substance in one liter of a [[solution]] is known as its [[molarity]]. Molarity is the common unit used to express the [[concentration]] of a solution in [[physical chemistry]].

===Chemical bond===

===Chemical bond===

A ''chemical bond'' is a concept for understanding how atoms stick together in molecules. It may be visualized as the [[multipole]] balance between the positive charges in the nuclei and the negative charges oscillating about them.<ref>visionlearning: Chemical Bonding by Anthony Carpi, Ph. [http://www.visionlearning.com/library/module_viewer.php?mid=55] More than simple attraction and repulsion, the energies and distributions characterize the availability of an electron to bond to another atom. These potentials create the [[interaction]]s which holds together [[atom]]s 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 predict molecular structure and composition. 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 fails and alternative approaches, primarily based on principles of [[quantum chemistry]] such as the [[molecular orbital]] theory, are necessary. See diagram on electronic orbitals.

A ''chemical bond'' is a concept for understanding how atoms stick together in molecules. It may be visualized as the [[multipole]] balance between the positive charges in the nuclei and the negative charges oscillating about them.<ref>visionlearning: Chemical Bonding by Anthony Carpi, Ph. [https://www.visionlearning.com/library/module_viewer.php?mid=55] More than simple attraction and repulsion, the energies and distributions characterize the availability of an electron to bond to another atom. These potentials create the [[interaction]]s which holds together [[atom]]s 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 predict molecular structure and composition. 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 fails and alternative approaches, primarily based on principles of [[quantum chemistry]] such as the [[molecular orbital]] theory, are necessary. See diagram on electronic orbitals.

===Chemical reaction===

===Chemical reaction===

''Chemical reaction'' is a concept related to the transformation of a [[chemical substance]] through its interaction with another, or  as a result of its interaction with some [[energy forms|form of energy]]. A chemical reaction may occur naturally or carried out in a laboratory by chemists in specially designed vessels which are often [[laboratory glassware]]. It 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 [[atom]]s within or across molecules. Chemical reactions usually involve the making or breaking of [[chemical bond]]s. [[Redox|Oxidation, reduction]], [[dissociation (chemistry)|dissociation]], acid-base [[neutralization]] and molecular [[rearrangement]] are some of the commonly used kinds of chemical reactions.

''Chemical reaction'' is a concept related to the transformation of a [[chemical substance]] through its interaction with another, or  as a result of its interaction with some [[energy forms|form of energy]]. A chemical reaction may occur naturally or carried out in a laboratory by chemists in specially designed vessels which are often [[laboratory glassware]]. It 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 [[atom]]s within or across molecules. Chemical reactions usually involve the making or breaking of [[chemical bond]]s. [[Redox|Oxidation, reduction]], [[dissociation (chemistry)|dissociation]], acid-base [[neutralization]] and molecular [[rearrangement]] are some of the commonly used kinds of 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. [http://goldbook.iupac.org/C01034.html Chemical Reaction Equation]- IUPAC Goldbook  

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. [https://goldbook.iupac.org/C01034.html Chemical Reaction Equation]- IUPAC Goldbook  

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.

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.

A stricter definition is that "a chemical reaction is a process that results in the interconversion of chemical species".[http://goldbook.iupac.org/C01033.html] Under this definition, 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').

A stricter definition is that "a chemical reaction is a process that results in the interconversion of chemical species".[https://goldbook.iupac.org/C01033.html] Under this definition, 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').

===Energy===

===Energy===

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 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]].

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 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 can be in the form of heat, light, [[electricity]] or mechanical [[force]] in the form of [[ultrasound]]. Reilly, Michael. (2007).

The activation energy necessary for a chemical reaction can be in the form of heat, light, [[electricity]] or mechanical [[force]] in the form of [[ultrasound]]. Reilly, Michael. (2007).

[http://www.newscientisttech.com/article/dn11427]

[https://www.newscientisttech.com/article/dn11427]

A related concept [[thermodynamic free energy|free energy]], which incorporates entropy considerations too, 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]].

A related concept [[thermodynamic free energy|free energy]], which incorporates entropy considerations too, 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 are only a 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 an 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 amenable to chemical reactions.   

There are only a 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 an 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 amenable to chemical reactions.   

The phase of a substance is invariably determined by its energy and those of its surroundings. When the intermolecular forces of a substance are such that 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 (H₂O), a liquid at room temperature because its molecules are bound by [[hydrogen bonds]].[http://www.chem4kids.com/files/matter_changes.html] - Chemforkids.com Whereas [[hydrogen sulfide]] (H₂S) is a gas at room temperature and standard pressure, as its molecules are bound by weaker [[Intermolecular force#Dipole-dipole interactions|dipole-dipole interactions]].  

The phase of a substance is invariably determined by its energy and those of its surroundings. When the intermolecular forces of a substance are such that 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 (H₂O), a liquid at room temperature because its molecules are bound by [[hydrogen bonds]].[https://www.chem4kids.com/files/matter_changes.html] - Chemforkids.com Whereas [[hydrogen sulfide]] (H₂S) is a gas at room temperature and standard pressure, as its molecules are bound by weaker [[Intermolecular force#Dipole-dipole interactions|dipole-dipole interactions]].  

The transfer of energy from one chemical substance to other depend on the ''size'' of energy [[quanta]] emitted from one substance. However, heat energy is easily transferred from almost any substance to another mainly because the vibrational and rotational energy levels in a substance are very closely placed. Because, the electronic energy levels are not so closely spaced, ultraviolet electromagnetic radiation is not transferred with equal felicity, as is also the case with electrical energy.

The transfer of energy from one chemical substance to other depend on the ''size'' of energy [[quanta]] emitted from one substance. However, heat energy is easily transferred from almost any substance to another mainly because the vibrational and rotational energy levels in a substance are very closely placed. Because, the electronic energy levels are not so closely spaced, ultraviolet electromagnetic radiation is not transferred with equal felicity, as is also the case with electrical energy.

==Subdisciplines==

==Subdisciplines==

Chemistry is typically divided into several major sub-disciplines. There are also several main cross-disciplinary and more specialized fields of chemistry. The Canadian Encyclopedia: Chemistry Subdisciplines [http://www.thecanadianencyclopedia.com/index.cfm?PgNm=TCE&Params=A1ARTA0001555]  

Chemistry is typically divided into several major sub-disciplines. There are also several main cross-disciplinary and more specialized fields of chemistry. The Canadian Encyclopedia: Chemistry Subdisciplines [https://www.thecanadianencyclopedia.com/index.cfm?PgNm=TCE&Params=A1ARTA0001555]  

* [[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.

* [[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.

==Chemical industry==

==Chemical industry==

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.[http://pubs.acs.org/cen/coverstory/83/8329globaltop50.html]

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.[https://pubs.acs.org/cen/coverstory/83/8329globaltop50.html]

==Further reading==

==Further reading==

==External links==

==External links==

*[http://www.iupac.org/dhtml_home.html International Union of Pure and Applied Chemistry]

*[https://www.iupac.org/dhtml_home.html International Union of Pure and Applied Chemistry]

*[http://www.chem.qmw.ac.uk/iupac/ IUPAC Nomenclature Home Page], see especially the "Gold Book" containing definitions of standard chemical terms

*[https://www.chem.qmw.ac.uk/iupac/ IUPAC Nomenclature Home Page], see especially the "Gold Book" containing definitions of standard chemical terms

*[http://hyperphysics.phy-astr.gsu.edu/hbase/chemical/chemcon.html#c1 Interactive [[Mind Map]] of Chemistry]

*[https://hyperphysics.phy-astr.gsu.edu/hbase/chemical/chemcon.html#c1 Interactive [[Mind Map]] of Chemistry]

*[http://www.smallscalechemistry.colostate.edu/PowerfulPictures/ChemicalEnergetics.pdf / Chemical energetics]

*[https://www.smallscalechemistry.colostate.edu/PowerfulPictures/ChemicalEnergetics.pdf / Chemical energetics]

[[Category: General Reference]]

[[Category: General Reference]]

[[Category: Chemistry]]

[[Category: Chemistry]]