Difference between revisions of "Chemistry" - New World Encyclopedia

Revision as of 15:51, 10 March 2006

Chemistry (in Greek: χημεία) is the science of matter that deals with the composition, structure, and properties of substances and with the transformations that they undergo. Chemistry also investigates the interaction of matter with energy (see physics, biology). In other words, chemistry is extremely important to understand and manipulate the "stuff" of the physical universe; as such it is often called the central science.

Introduction

File:Chemistry.jpg

Chemistry is a large field encompassing many sub-disciplines that often overlap with significant portions of other sciences. The fundamental component of chemistry is that it involves matter in some way (this explains its broad reach). It may involve the interaction of matter with non-material phenomenon, such as energy for example. More central to chemistry is the interaction of matter with other matter such as in the classic chemical reaction where chemical bonds are broken and made, forming new molecules.

Matter, such as the chair you are sitting in or the air you breathe, is today known to consist of atoms that combine together to form chemical compounds. Each atom consists of smaller bits of matter known as subatomic particles. The structure of the world we commonly experience and the properties of the matter we commonly interact with are determined by the nature of this matter on the chemical level. Steel is hard because of how the atoms are bound together. Wood will burn because it can react with oxygen in a chemical reaction. Water is a liquid at room temperature because of how each molecule of water interacts with its neighbors. In fact, you are a thinking, sentient being because of an on-going series of chemical reactions and other chemical interactions. You can see this text because of how light interacts with molecules called proteins in the back of your eye.

Chemistry is often called the central science because it connects to most of the other sciences. Chemistry is in some ways physics on a larger scale and in some ways is biology or geology on a smaller scale. Chemistry is used to understand and make better materials for engineering. It is used to understand the chemical mechanisms of disease as well as to create pharmaceuticals to treat disease. Chemistry is somehow involved in almost every science, every technology and every "thing."

With such a large area of study, it is impossible to know everything about chemistry and very difficult to summarize the field concisely. Even the most knowledgeable, experienced chemist only knows a very narrow area of chemistry better than others. Of course, most chemists have a broad general knowledge of many areas of chemistry as well. Chemistry is divided into many areas of study called sub-disciplines in which chemists specialize. The chemistry taught at the high school or early college level is often called "general chemistry" and is intended to be an introduction to a wide variety of fundamental concepts and to give the student the tools to continue on to more advanced subjects. Many concepts presented at this level are often incomplete and technically inaccurate, yet of extraordinary utility. Chemists regularly use these simple, elegant tools and explanations in their work when they suffice because the best solution possible is often so overwhelmingly difficult and the true solution is usually unobtainable.

Presented below are summaries and links to other articles that contain knowledge on a wide variety of sub-disciplines, techniques, theories, and tools used in chemistry. Although a good knowledge of chemistry only comes with many years of study, you may find small bits of knowledge here that may be helpful.

Subdisciplines of chemistry

Chemistry typically is divided into several major sub-disciplines. There are also several main cross-disciplinary and more specialized fields of chemistry.

Analytical chemistry: Analytical chemistry is the analysis of material samples to gain an understanding of their chemical composition and structure.

Biochemistry: Biochemistry is the study of the chemicals, chemical reactions, and chemical interactions that take place in living organisms.

Inorganic chemistry: Inorganic chemistry is the study of the properties and reactions of inorganic compounds. The distinction between organic and inorganic disciplines is not absolute and there is much overlap, most importantly in the sub-discipline of organometallic chemistry.

Organic chemistry: Organic chemistry is the study of the structure, properties, composition, mechanisms, and reactions of organic compounds.

Physical chemistry: Physical chemistry is the study of the physical basis of chemical systems and processes. In particular, the energetic description of diverse chemical transformations is of interest to physical chemists. Important areas of study include chemical thermodynamics, chemical kinetics, statistical mechanics, and spectroscopy. Physical chemistry has large overlap with molecular physics.

Theoretical chemistry: Theoretical chemistry is the study of chemistry via 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 Second World War, the development of computers has allowed a systematic development of computational chemistry, which is the art of developing and applying computer programs for solving chemical problems. Theoretical chemistry has large overlap with molecular physics.

Other fields: Astrochemistry, atmospheric chemistry, chemical Engineering, electrochemistry, environmental chemistry, geochemistry, history of chemistry, materials science, medicinal chemistry, molecular biology, molecular genetics, nuclear chemistry, organometallic chemistry, petrochemistry, pharmacology, photochemistry, phytochemistry, polymer chemistry, supramolecular chemistry, surface chemistry, and thermochemistry.

Fundamental concepts

Nomenclature

Nomenclature refers to the system for naming chemical compounds. There are well-defined systems in place for naming chemical species. Organic compounds are named according to the organic nomenclature system. Inorganic compounds are named according to the inorganic nomenclature system.

See also: IUPAC nomenclature

Atoms

Main article: Atom.

An atom is a collection of matter consisting of a positively charged core (the nucleus), which contains protons and neutrons, and which maintains a number of electrons to balance the positive charge in the nucleus.

Elements

Main article: Chemical element.

An element is a class of atoms which have the same number of protons in the nucleus. This number is known as the atomic number of the element. For example, all atoms with 6 protons in their nuclei are atoms of the chemical element carbon, and all atoms with 92 protons in their nuclei are atoms of the element uranium.

The most convenient presentation of the elements is in the periodic table, which groups elements with similar chemical properties together. Lists of the elements by name, by symbol, and by atomic number are also available.

Because the number of protons in the nucleus dictates the number of electrons surrounding the nucleus and their properties, and because the electrons are the outermost component of atoms (the component which presents a surface to the rest of the universe), the identity of an element dictates the interactions, or chemical transformations, in which it can participate. There may, however, be subtle changes in chemical properties brought about by the number of neutrons in the nucleus of otherwise "same" elements.

See also: isotope

Compounds

Main article: Chemical compound

A compound is a substance with a fixed ratio of elements which determines the composition, and a particular organization which determines chemical properties. For example, water is a compound containing hydrogen and oxygen in the ratio of two to one. Compounds are formed and interconverted by chemical reactions.

Molecules

Main article: Molecule.

A molecule is the smallest indivisible portion of a pure compound that retains a set of unique chemical properties. A molecule consists of two or more atoms bonded together.

Ions

Main article: Ion.

An ion is a charged species, or an atom or a molecule that has lost or gained an electron. Positively charged cations (e.g., sodium cation Na⁺) and negatively charged anions (e.g., chloride Cl^-) build neutral salts (e.g., sodium chloride NaCl). Examples of polyatomic ions that do not split up during acid-base reactions are hydroxide (OH^-), or phosphate (PO₄^3-).

Bonding

Main article: Chemical bond.

A chemical bond is the force which holds together atoms in molecules or crystals. In many simple compounds, valence bond theory 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 metal complexes, valence bond theory fails and alternative approaches that are based on quantum chemistry, such as molecular orbital theory, are necessary.

States of matter

Main article: Phase (matter).

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 state. When three states meet based on these 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 solids, liquids, and gases. Less familiar phases include plasmas, Bose-Einstein condensates and fermionic condensates, and the paramagnetic and ferromagnetic phases of magnetic materials. Even the familiar ice has many different phases depending on the pressure and temperature of the system. While most familiar phases deal with three-dimensional systems, it is also possible to define analogs in two-dimensional systems, which is getting a lot of attention because of its relevance to biology.

Chemical Reactions

Main article: Chemical reaction.

Chemical reactions are transformations in the fine structure of molecules. Such reactions can result in molecules attaching to each other to form larger molecules, molecules breaking apart to form two or more smaller molecules, or rearrangement of atoms within or across molecules. Chemical reactions usually involve the making or breaking of chemical bonds.

Quantum chemistry

Main article: Quantum chemistry.

Quantum chemistry describes the behavior of matter at the molecular scale. It is, in principle, possible to describe all chemical systems using this theory. In practice, only the simplest chemical systems may realistically be investigated in purely quantum mechanical terms, and approximations must be made for most practical purposes (e.g., Hartree-Fock, post Hartree-Fock, or Density functional theory, see computational chemistry for more details). Hence a detailed understanding of quantum mechanics is not necessary for most chemistry, as the important implications of the theory (principally the orbital approximation) can be understood and applied in simpler terms.

Laws

The most fundamental concept in chemistry is the law of conservation of mass, which states that there is no detectable change in the quantity of matter during an ordinary chemical reaction. Modern physics shows that it is actually energy that is conserved, and that energy and mass are related; a concept which becomes important in nuclear chemistry. Conservation of energy leads to the important concepts of equilibrium, thermodynamics, and kinetics.

Further laws of chemistry elaborate on the law of conservation of mass. Joseph Proust's law of definite composition says that pure chemicals are composed of elements in a definite formulation; we now know that the structural arrangement of these elements is also important.

Dalton's law of multiple proportions says that these chemicals will present themselves in proportions that are small whole numbers (i.e., 1:2 O:H in water); although for biomacromolecules and mineral chemistry the ratios tend to require large numbers.

More modern laws of chemistry define the relationship between energy and transformations.

In equilibrium, molecules exist in mixture defined by the transformations possible on the timescale of the equilibrium, and are in a ratio defined by the intrinsic energy of the molecules—the lower the intrinsic energy, the more abundant the molecule.
Transforming one structure to another requires the input of energy to cross an energy barrier; this can come from the intrinsic energy of the molecules themselves, or from an external source that will generally accelerate transformations. The higher the energy barrier, the slower the transformation occurs.
There is a hypothetical intermediate, or transition structure, that corresponds to the structure at the top of the energy barrier. The Hammond-Leffler Postulate states that this structure looks most similar to the product or starting material that has intrinsic energy closest to that of the energy barrier. Stabilizing this hypothetical intermediate through chemical interaction is one way to achieve catalysis.
All chemical processes are reversible (law of microscopic reversibility), although some processes have such an energy bias, they are essentially irreversible.

History of chemistry

Alchemy
Discovery of the chemical elements
History of chemistry
Nobel Prize in chemistry
Timeline of chemical element discovery

Etymology

Old French: alkemie; Arab al-kimia: the art of transformation. See also: alchemy

External links

Chemical Glossary
Chemistry Information Database, includes basic information and some toxicity
IUPAC Nomenclature Home Page, see especially the "Gold Book" containing definitions of standard chemical terms
CCI Project, videos and photos of chemistry experiments
Material safety data sheets for a variety of chemicals
Material Safety Data Sheets

Credits

New World Encyclopedia writers and editors rewrote and completed the Wikipedia article in accordance with New World Encyclopedia standards. This article abides by terms of the Creative Commons CC-by-sa 3.0 License (CC-by-sa), which may be used and disseminated with proper attribution. Credit is due under the terms of this license that can reference both the New World Encyclopedia contributors and the selfless volunteer contributors of the Wikimedia Foundation. To cite this article click here for a list of acceptable citing formats.The history of earlier contributions by wikipedians is accessible to researchers here:

Chemistry ^history

The history of this article since it was imported to New World Encyclopedia:

History of "Chemistry"

Note: Some restrictions may apply to use of individual images which are separately licensed.

@@ Line 1: / Line 1: @@
-{{Paid}}{{Images OK}} {{Approved}} {{submitted}} {{Contracted}} {{Status}}'''Chemistry''' (in [[Greek language|Greek]]: ''&#967;&#951;&#956;&#949;&#943;&#945;'') is the [[science]] of [[matter]] that deals with the composition, structure, and properties of [[Chemical substance|substance]]s and with the [[chemical transformation|transformation]]s that they undergo. Chemistry also investigates the interaction of matter with [[energy]] (see [[physics]], [[biology]]). In other works chemistry is extremly important to understand and manipulate the "stuff" of the phyical universe. As such it is often called the central science.
+{{Copyedited}}{{Paid}}{{Images OK}}{{Approved}}{{Submitted}}{{Contracted}}{{Status}}
+'''Chemistry''' (in [[Greek language|Greek]]: ''&#967;&#951;&#956;&#949;&#943;&#945;'') is the [[science]] of [[matter]] that deals with the composition, structure, and properties of [[Chemical substance|substance]]s and with the [[chemical transformation|transformation]]s that they undergo. Chemistry also investigates the interaction of matter with [[energy]] (see [[physics]], [[biology]]). In other words, chemistry is extremely important to understand and manipulate the "stuff" of the physical universe; as such it is often called the central science.
 == Introduction ==
 [[Image:Chemistry.jpg|right|thumb|]]
-Chemistry is a large field encompassing many subdisciplines that often overlap with significant portions of other sciences. The fundamental component of chemistry is that it involves matter in some way (this explains its broad reach). It may involve the interaction of matter with non-material phenomenon, such as energy for example. More central to chemistry is the interaction of matter with matter such as in the classic [[chemical reaction]] where [[chemical bond]]s are broken and made, forming new molecules.
+Chemistry is a large field encompassing many sub-disciplines that often overlap with significant portions of other sciences. The fundamental component of chemistry is that it involves matter in some way (this explains its broad reach). It may involve the interaction of matter with non-material phenomenon, such as energy for example. More central to chemistry is the interaction of matter with other matter such as in the classic [[chemical reaction]] where [[chemical bond]]s are broken and made, forming new molecules.
-Matter, such as the chair you are sitting in or the air you breathe, is today known to consist of [[atom]]s that combine together to form [[chemical compounds]]. Each atom consists of smaller bits of matter known as [[subatomic particles]]. The structure of the world we commonly experience and the properties of the matter we commonly interact with are determined by the nature of this matter on the chemical level. [[Steel]] is hard because of how the atoms are bound together. Wood will burn because it can react with [[oxygen]] in a chemical reaction. Water is a [[liquid]] at room temperature because of how each molecule of water interacts with its neighbors. In fact, you are a thinking, sentient being because of an on-going series of chemical reactions and other chemical interactions. You can see this text because of how light interacts with molecules called [[proteins]] in the back of your eye.
+Matter, such as the chair you are sitting in or the air you breathe, is today known to consist of [[atom]]s that combine together to form [[chemical compound]]s. Each atom consists of smaller bits of matter known as [[subatomic particle]]s. The structure of the world we commonly experience and the properties of the matter we commonly interact with are determined by the nature of this matter on the chemical level. [[Steel]] is hard because of how the atoms are bound together. Wood will burn because it can react with [[oxygen]] in a chemical reaction. Water is a [[liquid]] at room temperature because of how each molecule of water interacts with its neighbors. In fact, you are a thinking, sentient being because of an on-going series of chemical reactions and other chemical interactions. You can see this text because of how light interacts with molecules called [[proteins]] in the back of your eye.
-Chemistry is often called the central science because it connects to most of the other sciences. Chemistry is in some ways [[physics]] on a larger scale and in some ways is [[biology]] or [[geology]] on a smaller scale. Chemistry is used to understand and make better materials for [[engineering]]. It is used to understand the chemical mechanisms of disease as well as to create [[pharmaceuticals]] to treat disease. Chemistry is somehow involved in almost every science, every technology and every "thing".
+Chemistry is often called the central science because it connects to most of the other sciences. Chemistry is in some ways [[physics]] on a larger scale and in some ways is [[biology]] or [[geology]] on a smaller scale. Chemistry is used to understand and make better materials for [[engineering]]. It is used to understand the chemical mechanisms of disease as well as to create [[pharmaceuticals]] to treat disease. Chemistry is somehow involved in almost every science, every technology and every "thing."
-With such a large area of study, it is impossible to know everything about chemistry and very difficult to summarize the field concisely. Even the most knowledgable, experienced chemist only knows a very narrow area of chemistry better than others. Of course, most chemists have a broad general knowledge of many areas of chemistry as well. Chemistry is divided into many areas of study called subdisciplines in which chemists specialize. The chemistry taught at the high school or early college level is often called "general chemistry" and is intended to be an introduction to a wide variety of fundamental concepts and to give the student the tools to continue on to more advanced subjects. Many concepts presented at this level are often incomplete and technically inaccurate yet of extraordinary utility. Chemists regularly use these simple, elegant tools and explanations in their work when they suffice because the best solution possible is often so overwhelmingly difficult and the true solution is usually unobtainable.
+With such a large area of study, it is impossible to know everything about chemistry and very difficult to summarize the field concisely. Even the most knowledgeable, experienced chemist only knows a very narrow area of chemistry better than others. Of course, most chemists have a broad general knowledge of many areas of chemistry as well. Chemistry is divided into many areas of study called sub-disciplines in which chemists specialize. The chemistry taught at the high school or early college level is often called "general chemistry" and is intended to be an introduction to a wide variety of fundamental concepts and to give the student the tools to continue on to more advanced subjects. Many concepts presented at this level are often incomplete and technically inaccurate, yet of extraordinary utility. Chemists regularly use these simple, elegant tools and explanations in their work when they suffice because the best solution possible is often so overwhelmingly difficult and the true solution is usually unobtainable.
-Presented below are summaries and links to other articles that contain knowledge on a wide variey of subdisciplines, techniques, theories and tools used in chemistry. Although a good knowledge of chemistry only comes with many years of study, you may find small bits of knowledge here that may be helpful.
+Presented below are summaries and links to other articles that contain knowledge on a wide variety of sub-disciplines, techniques, theories, and tools used in chemistry. Although a good knowledge of chemistry only comes with many years of study, you may find small bits of knowledge here that may be helpful.
 == Subdisciplines of chemistry ==
@@ Line 19: / Line 20: @@
 ; [[Analytical chemistry]] : ''Analytical chemistry'' is the [[analysis]] of material samples to gain an understanding of their [[chemical composition]] and [[structure]].
-; [[Biochemistry]] : ''Biochemistry'' is the study of the [[chemical compound|chemicals]], [[chemical reaction]]s and chemical [[interaction]]s that take place in living [[organism]]s.
+; [[Biochemistry]] : ''Biochemistry'' is the study of the [[chemical compound|chemicals]], [[chemical reaction]]s, and chemical [[interaction]]s that take place in living [[organism]]s.
 ; [[Inorganic chemistry]] : ''Inorganic chemistry'' is the study of the properties and reactions of inorganic compounds. The distinction between organic and inorganic disciplines is not absolute and there is much overlap, most importantly in the sub-discipline of [[organometallic chemistry]].
@@ Line 25: / Line 26: @@
 ; [[Organic chemistry]] : ''Organic chemistry'' is the study of the structure, properties, composition, mechanisms, and [[chemical reaction|reactions]] of [[organic compound]]s.
-; [[Physical chemistry]] : ''Physical chemistry'' is the study of the physical basis of chemical systems and processes.  In particular, the energetic description of diverse chemical transformations are of interest to physical chemists.  Important areas of study include [[chemical thermodynamics]], [[chemical kinetics]], [[statistical mechanics]], and [[spectroscopy]].  Physical chemistry has large overlap with [[molecular physics]].
+; [[Physical chemistry]] : ''Physical chemistry'' is the study of the physical basis of chemical systems and processes. In particular, the energetic description of diverse chemical transformations is of interest to physical chemists. Important areas of study include [[chemical thermodynamics]], [[chemical kinetics]], [[statistical mechanics]], and [[spectroscopy]]. Physical chemistry has large overlap with [[molecular physics]].
-; [[Theoretical chemistry]] : ''Theoretical chemistry'' is the study of chemistry via 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 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 [[molecular physics]].
+; [[Theoretical chemistry]] : ''Theoretical chemistry'' is the study of chemistry via 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 [[computer]]s 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 [[molecular physics]].
-; Other fields : [[Astrochemistry]], [[Atmospheric chemistry]], [[Chemical Engineering]], [[Electrochemistry]], [[Environmental chemistry]], [[Geochemistry]], [[History of chemistry]], [[Materials science]], [[Medicinal chemistry]], [[Molecular Biology]], [[Molecular genetics]], [[Nuclear chemistry]], [[Organometallic chemistry]], [[Petrochemistry]], [[Pharmacology]], [[Photochemistry]], [[Phytochemistry]], [[Polymer chemistry]], [[Supramolecular chemistry]], [[Surface chemistry]], and [[Thermochemistry]].
+; Other fields : [[Astrochemistry]], [[atmospheric chemistry]], [[chemical Engineering]], [[electrochemistry]], [[environmental chemistry]], [[geochemistry]], [[history of chemistry]], [[materials science]], [[medicinal chemistry]], [[molecular biology]], [[molecular genetics]], [[nuclear chemistry]], [[organometallic chemistry]], [[petrochemistry]], [[pharmacology]], [[photochemistry]], [[phytochemistry]], [[polymer chemistry]], [[supramolecular chemistry]], [[surface chemistry]], and [[thermochemistry]].
 == Fundamental concepts ==
@@ Line 43: / Line 44: @@
 ''Main article: [[Atom]].''
-An ''atom'' is a collection of matter consisting of a positively charged core (the [[nucleus]]) which contains [[proton]]s and [[neutron]]s, and which maintains a number of [[electron]]s to balance the positive charge in the nucleus.
+An '''atom''' is a collection of matter consisting of a positively charged core (the [[nucleus]]), which contains [[proton]]s and [[neutron]]s, and which maintains a number of [[electron]]s to balance the positive charge in the nucleus.
 === Elements ===
@@ Line 49: / Line 50: @@
 ''Main article: [[Chemical element]].''
-An ''element'' is a class of atoms which have the same number of [[proton]]s in the [[atomic nucleus|nucleus]]. This number is known as the [[atomic number]] of the element. For example, all atoms with 6 protons in their nuclei are atoms of the chemical element [[carbon]], and all atoms with 92 protons in their nuclei are atoms of the element [[uranium]].
+An '''element''' is a class of atoms which have the same number of [[proton]]s in the [[atomic nucleus|nucleus]]. This number is known as the [[atomic number]] of the element. For example, all atoms with 6 protons in their nuclei are atoms of the chemical element [[carbon]], and all atoms with 92 protons in their nuclei are atoms of the element [[uranium]].
-The most convenient presentation of the elements is in the [[periodic table]], which groups elements with similar chemical properties together. Lists of the elements [[List of elements by name|by name]], [[List of elements by symbol|by symbol]], and by [[List of elements by number|atomic number]] are also available.
+The most convenient presentation of the elements is in the [[periodic table]], which groups elements with similar chemical properties together. Lists of the elements [[List of elements by name|by name]], [[List of elements by symbol|by symbol]], and [[List of elements by number|by atomic number]] are also available.
-Because the number of protons in the nucleus dictates the number of electrons surrounding the nucleus and their properties, and because the electrons are the outermost component of atoms (the component which presents a surface to the rest of the universe), the identity of an element dictates the interactions, or chemical transformations, in which it can participate.  There may, however, be subtle changes in chemical properties brought about by the number of neutrons in the nucleus of otherwise "same" elements.
+Because the number of protons in the nucleus dictates the number of electrons surrounding the nucleus and their properties, and because the electrons are the outermost component of atoms (the component which presents a surface to the rest of the universe), the identity of an element dictates the interactions, or chemical transformations, in which it can participate. There may, however, be subtle changes in chemical properties brought about by the number of neutrons in the nucleus of otherwise "same" elements.
 ''See also: [[isotope]]''
@@ Line 61: / Line 62: @@
 ''Main article: [[Chemical compound]]''
-A ''compound'' is a substance with a ''fixed ratio'' of [[element]]s which determines the composition, and a particular organisation which determines chemical properties. For example, [[water (molecule)|water]] is a compound containing [[hydrogen]] and [[oxygen]] in the ratio of two to one. Compounds are formed and interconverted by [[chemical reaction]]s.
+A '''compound''' is a substance with a ''fixed ratio'' of [[element]]s which determines the composition, and a particular organization which determines chemical properties. For example, [[water (molecule)|water]] is a compound containing [[hydrogen]] and [[oxygen]] in the ratio of two to one. Compounds are formed and interconverted by [[chemical reaction]]s.
 === Molecules ===
@@ Line 67: / Line 68: @@
 ''Main article: [[Molecule]].''
-A ''molecule'' is the smallest indivisible portion of a pure [[Chemical compound|compound]] that retains a set of unique chemical properties.  A molecule consists of two or more [[atom]]s [[Chemical bond|bonded]] together.
+A '''molecule''' is the smallest indivisible portion of a pure [[Chemical compound|compound]] that retains a set of unique chemical properties. A molecule consists of two or more [[atom]]s [[Chemical bond|bonded]] together.
 === Ions ===
@@ Line 73: / Line 74: @@
 ''Main article: [[Ion (physics)|Ion]].''
-An ''ion'' is a charged species, or an atom or a molecule that has lost or gained an electron. Positively charged [[cations]] (e.g. [[sodium]] cation Na<sup>+</sup>) and negatively charged [[anions]] (e.g. [[chloride]] Cl<sup>-</sup>) build neutral [[Salt|salts]] (e.g. [[sodium chloride]] NaCl). Examples of [[polyatomic ion]]s that do not split up during [[Acid-base reaction theories|acid-base reactions]] are [[hydroxide]] (OH<sup>-</sup>), or [[phosphate]] (PO<sub>4</sub><sup>3-</sup>).
+An '''ion''' is a charged species, or an atom or a molecule that has lost or gained an electron. Positively charged [[cations]] (e.g., [[sodium]] cation Na<sup>+</sup>) and negatively charged [[anions]] (e.g., [[chloride]] Cl<sup>-</sup>) build neutral [[salt]]s (e.g., [[sodium chloride]] NaCl). Examples of [[polyatomic ion]]s that do not split up during [[Acid-base reaction theories|acid-base reactions]] are [[hydroxide]] (OH<sup>-</sup>), or [[phosphate]] (PO<sub>4</sub><sup>3-</sup>).
 === Bonding ===
@@ Line 79: / Line 80: @@
 ''Main article: [[Chemical bond]].''
-A ''chemical bond'' is the force which holds together [[atom]]s in [[molecule]]s or [[crystal]]s. In many simple compounds, [[valence bond theory]] 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 which are based on [[quantum chemistry]], such as [[molecular orbital]] theory, are necessary.
+A '''chemical bond''' is the force which holds together [[atom]]s in [[molecule]]s or [[crystal]]s. In many simple compounds, [[valence bond theory]] 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 that are based on [[quantum chemistry]], such as [[molecular orbital]] theory, are necessary.
 === States of matter ===
@@ Line 85: / Line 86: @@
 ''Main article: [[Phase (matter)]].''
-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.
+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]] 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.
+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]] state. When three states meet based on these 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. Less familiar phases include [[Plasma physics|plasma]]s, [[Bose-Einstein condensate]]s and [[fermionic condensate]]s and the [[paramagnetism|paramagnetic]] and [[ferromagnetism|ferromagnetic]] phases of [[magnet]]ic materials.  Even the familiar [[ice]] has many different phases, depending on the pressure and temperature of the system.  While most familiar phases deal with three-dimensional systems, it is also possible to define analogs in two-dimensional systems, which is getting a lot of attention because of its relevance to [[biology]].
+The most familiar examples of phases are [[solid]]s, [[liquid]]s, and [[gas]]es. Less familiar phases include [[Plasma physics|plasma]]s, [[Bose-Einstein condensate]]s and [[fermionic condensate]]s, and the [[paramagnetism|paramagnetic]] and [[ferromagnetism|ferromagnetic]] phases of [[magnet]]ic materials. Even the familiar [[ice]] has many different phases depending on the pressure and temperature of the system. While most familiar phases deal with three-dimensional systems, it is also possible to define analogs in two-dimensional systems, which is getting a lot of attention because of its relevance to [[biology]].
 === Chemical Reactions ===
@@ Line 95: / Line 96: @@
 ''Main article: [[Chemical reaction]].''
-''Chemical reactions'' are transformations in the fine [[structure]] of [[molecule]]s.  Such reactions can result in molecules attaching to each other to form larger molecules, 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.
+'''Chemical reactions''' are transformations in the fine [[structure]] of [[molecule]]s. Such reactions can result in molecules attaching to each other to form larger molecules, 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.
-=== Quantum chemistry  ===
+=== Quantum chemistry ===
 ''Main article: [[Quantum chemistry]].''
-''Quantum chemistry'' describes the behavior of [[matter]] at the [[molecule | molecular]] scale. It is, in principle, possible to describe all chemical systems using this theory. In practice, only the simplest chemical systems may realistically be investigated in purely [[quantum mechanics | quantum mechanical]] terms, and approximations must be made for most practical purposes (e.g., [[Hartree-Fock]], [[post Hartree-Fock]] or [[Density functional theory]], see [[computational chemistry]] for more details). Hence a detailed understanding of [[quantum mechanics]] is not necessary for most chemistry, as the important implications of the theory (principally the [[atomic orbital|orbital approximation]]) can be understood and applied in simpler terms.
+'''Quantum chemistry''' describes the behavior of [[matter]] at the [[molecule|molecular]] scale. It is, in principle, possible to describe all chemical systems using this theory. In practice, only the simplest chemical systems may realistically be investigated in purely [[quantum mechanics|quantum mechanical]] terms, and approximations must be made for most practical purposes (e.g., [[Hartree-Fock]], [[post Hartree-Fock]], or [[Density functional theory]], see [[computational chemistry]] for more details). Hence a detailed understanding of [[quantum mechanics]] is not necessary for most chemistry, as the important implications of the theory (principally the [[atomic orbital|orbital approximation]]) can be understood and applied in simpler terms.
 === Laws ===
-The most fundamental concept in chemistry is the [[law of conservation of mass]], which states that there is no detectable change in the quantity of matter during an ordinary [[chemical reaction]]. Modern physics shows that it is actually [[energy]] that is conserved, and that energy and mass are [[Einstein#Energy equivalency|related]]; a concept which becomes important in [[nuclear chemistry]]. [[Conservation of energy]] leads to the important concepts of [[Chemical equilibrium|equilibrium]], [[thermodynamics]], and [[chemical kinetics|kinetics]].
+The most fundamental concept in chemistry is the [[law of conservation of mass]], which states that there is no detectable change in the quantity of matter during an ordinary [[chemical reaction]]. Modern physics shows that it is actually [[energy]] that is conserved, and that energy and mass are [[Albert Einstein#Energy equivalency|related]]; a concept which becomes important in [[nuclear chemistry]]. [[Conservation of energy]] leads to the important concepts of [[Chemical equilibrium|equilibrium]], [[thermodynamics]], and [[chemical kinetics|kinetics]].
-Further laws of chemistry elaborate on the law of conservation of mass.  [[Joseph Proust]]'s [[law of definite composition]] says that pure chemicals are composed of elements in a definite formulation; we now know that the structural arrangement of these elements is also important.
+Further laws of chemistry elaborate on the law of conservation of mass. [[Joseph Proust]]'s [[law of definite composition]] says that pure chemicals are composed of elements in a definite formulation; we now know that the structural arrangement of these elements is also important.
-[[John_Dalton|Dalton]]'s [[law of multiple proportions]] says that these chemicals will present themselves in proportions that are small whole numbers (i.e. 1:2 O:H in water); although for biomacromolecules and mineral chemistry the ratios tend to require large numbers.
+[[John Dalton|Dalton]]'s [[law of multiple proportions]] says that these chemicals will present themselves in proportions that are small whole numbers (i.e., 1:2 O:H in water); although for biomacromolecules and mineral chemistry the ratios tend to require large numbers.
 More modern laws of chemistry define the relationship between energy and transformations.
 * In equilibrium, molecules exist in mixture defined by the transformations possible on the timescale of the equilibrium, and are in a ratio defined by the intrinsic energy of the molecules&mdash;the lower the intrinsic energy, the more abundant the molecule.
-* Transforming one structure to another requires the input of energy to cross an energy barrier; this can come from the intrinsic energy of the molecules themselves, or from an external source which will generally accelerate transformations.  The higher the energy barrier, the slower the transformation occurs.
+* Transforming one structure to another requires the input of energy to cross an energy barrier; this can come from the intrinsic energy of the molecules themselves, or from an external source that will generally accelerate transformations. The higher the energy barrier, the slower the transformation occurs.
-* There is a hypothetical intermediate, or ''transition structure'', that corresponds to the structure at the top of the energy barrier.  The [[Hammond-Leffler Postulate]] states that this structure looks most similar to the product or starting material which has intrinsic energy closest to that of the energy barrier.  Stabilizing this hypothetical intermediate through chemical interaction is one way to achieve [[catalysis]].
+* There is a hypothetical intermediate, or ''transition structure,'' that corresponds to the structure at the top of the energy barrier. The [[Hammond-Leffler Postulate]] states that this structure looks most similar to the product or starting material that has intrinsic energy closest to that of the energy barrier. Stabilizing this hypothetical intermediate through chemical interaction is one way to achieve [[catalysis]].
-* All chemical processes are reversible (law of [[microscopic reversibility]]) although some processes have such an energy bias, they are essentially irreversible.
+* All chemical processes are reversible (law of [[microscopic reversibility]]), although some processes have such an energy bias, they are essentially irreversible.
 == History of chemistry ==
@@ Line 130: / Line 131: @@
 == See also ==
-* [[American Chemical Society]]
 * [[Chemical engineering]]
-* [[International Union of Pure and Applied Chemistry]]
 * [[Periodic table]]
@@ Line 138: / Line 137: @@
 * [http://www.allchemicals.info/ Chemical Glossary]
-* [http://chem.sis.nlm.nih.gov/chemidplus/ Chemistry Information Database includes basic information and some toxicity]
+* [http://chem.sis.nlm.nih.gov/chemidplus/ Chemistry Information Database, includes basic information and some toxicity]
 * [http://www.chem.qmw.ac.uk/iupac/ IUPAC Nomenclature Home Page], see especially the "Gold Book" containing definitions of standard chemical terms
-* [http://www.cci.ethz.ch/index.html Experiments] videos and photos of the techniques and results
+* [http://www.cci.ethz.ch/index.html CCI Project], videos and photos of chemistry experiments
 * [http://physchem.ox.ac.uk/MSDS/ Material safety data sheets for a variety of chemicals]
 * [http://www.flinnsci.com/search_MSDS.asp Material Safety Data Sheets]