Molecule 19555 225219611 2008-07-12T15:03:24Z ClueBot 4928500 Reverting possible vandalism by [[Special:Contributions/124.106.150.56|124.106.150.56]] to version by Littlealien182. False positive? [[User:ClueBot/FalsePositives|Report it]]. Thanks, [[User:ClueBot]]. (438579) (Bot) [[Image:Atisane3.png|thumb|350px|[[Three-dimensional space|3D]] (left and center) and [[2D geometric model|2D]] (right) representations of the [[terpenoid]] molecule atisane.]] In [[chemistry]], a '''molecule''' is defined as a sufficiently stable [[electric charge|electrically]] neutral group of at least two [[atom]]s in a definite arrangement held together by very strong [[chemical bond]]s . It can also be defined as a unit of two or more atoms held together by covalent bonds.<ref name="iupac">{{GoldBookRef|title=molecule|url=http://goldbook.iupac.org/M04002.html|year=1994}}</ref><ref>{{cite book|author=Pauling, Linus |title=General Chemistry|location=New York | publisher=Dover Publications, Inc.|year=1970|id=ISBN 0-486-65622-5}}<br> {{cite book| author=Ebbin, Darrell, D. |title=General Chemistry, 3th Ed.|location=Boston | publisher=Houghton Mifflin Co.|year=1990|id=ISBN 0-395-43302-9}}<br>{{cite book|author=Brown, T.L. |title=Chemistry – the Central Science, 9th Ed.|location=New Jersey | publisher=Prentice Hall|year=2003|id=ISBN 0-13-066997-0}}<br>{{cite book|author=Chang, Raymond |title=Chemistry, 6th Ed.|location=New York | publisher=McGraw Hill|year=1998|id=ISBN 0-07-115221-0}}<br>{{cite book|author=Zumdahl, Steven S. |title= Chemistry, 4th ed.|location= Boston |publisher= Houghton Mifflin|year= 1997|id=ISBN 0-669-41794-7}}</ref> In [[organic chemistry]] and [[biochemistry]], the term ''molecule'' is used less strictly and also is applied to charged [[organic compound|organic molecules]] and [[biomolecule]]s. Molecules are distinguished from [[polyatomic ion]]s in this strict sense. This definition has evolved as knowledge of the structure of molecules has increased. Earlier definitions were less precise defining molecules as the smallest [[list of particles#Molecules|particles]] of pure [[chemical substance]]s that still retain their [[chemical compound|composition]] and chemical properties.<ref>[http://antoine.frostburg.edu/chem/senese/101/glossary/m.shtml#molecule Molecule Definition] (Frostburg State University)</ref> This definition often breaks down since many substances in ordinary experience, such as [[rock (geology)|rock]]s, [[salt (chemistry)|salt]]s, and [[metal]]s, are composed of atoms or [[ion]]s, but are not made of molecules. In the [[kinetic theory]] of [[gas]]es the term ''molecule'' is often used for any gaseous particle regardless of their composition.<ref>E.g. see [http://www.usd.edu/phys/courses/phys_111sf/ch_10/10_notes.htm]</ref> According to this definition [[noble gas]]es would also be considered ''molecules'' despite the fact that they are composed of a single non-bonded atom. == History == {{main|History of the molecule}} The term "'''molecule'''", from the French ''molécule'' meaning "extremely minute particle," was coined by French philosopher [[Rene Descartes]] in the 1620s. Although the existence of molecules was accepted by many chemists since the early 19th century as a result of [[John Dalton|Dalton's]] laws of Definite and Multiple Proportions (1803-1808) and [[Avogadro's law]] (1811), there was some resistance among [[logical positivism|positivists]] and physicists such as [[Ernst Mach|Mach]], [[Ludwig Boltzmann|Boltzmann]], [[James Clerk Maxwell|Maxwell]], and [[Willard Gibbs|Gibbs]], who saw molecules merely as convenient mathematical constructs. The work of [[Jean Perrin|Perrin]] on Brownian motion (1911) is considered to be the final proof of the existence of molecules. In a molecule, at least two atoms are joined by shared pairs of [[electron]]s in a [[covalent bond]]. It may consist of atoms of the same [[chemical element]], as with [[oxygen]] (O<sub>2</sub>), or of different elements, as with [[water (molecule)|water]] (H<sub>2</sub>O). Atoms and complexes connected by non-covalent bonds such as [[hydrogen bond]]s or [[ionic bond]]s are generally not considered single molecules. No typical molecule can be defined for ionic ([[salt (chemistry)|salts]]) and covalent crystals ([[network solids]]) which are composed of repeating [[unit cell]]s that extend either in a [[Plane (mathematics)|plane]] (such as in [[graphite]]) or three-dimensionally (such as in [[diamond]] or [[sodium chloride]]). The science of molecules is called ''molecular chemistry'' or ''[[molecular physics]]'', depending on the focus. Molecular chemistry deals with the laws governing the interaction between molecules that results in the formation and breakage of [[chemical bond]]s, while molecular physics deals with the laws governing their structure and properties. In practice, however, this distinction is vague. In molecular sciences, a molecule consists of a stable system ([[bound state]]) comprising two or more [[atom]]s. [[Polyatomic ion]]s may sometimes be usefully thought of as electrically charged molecules. The term ''unstable molecule'' is used for very [[reactivity|reactive]] species, i.e., short-lived assemblies ([[resonance]]s) of electrons and [[atomic nucleus|nuclei]], such as [[radical (chemistry)|radicals]], molecular [[ion]]s, [[Rydberg molecule]]s, [[transition state]]s, [[van der Waals bonding|van der Waals complex]]es, or systems of colliding atoms as in [[Bose-Einstein condensate]]s. == Molecular size == Most molecules are far too small to be seen with the opened eye, but there are exceptions. [[DNA]], a [[macromolecule]], can reach [[macroscopic]] sizes, as can molecules of many polymers. The smallest molecule is the [[diatomic]] [[hydrogen]] (H<sub>2</sub>), with an overall length of roughly twice the 74 [[picometre]]s (0.74 [[Ångström|Å]]) bond length. Molecules commonly used as building blocks for organic synthesis have a dimension of a few Å to several dozen Å. Single molecules cannot usually be observed by light (as noted above), but small molecules and even the outlines of individual atoms may be traced in some circumstances by use of an [[atomic force microscope]]. Some of the largest molecules are [[macromolecule]]s or [[supermolecule]]s. ===Radius=== ''Effective molecular radius'' is the size a molecule displays in solution. <ref> [www.wipo.int/pctdb/en/wo.jsp?IA=WO1999030745&DISPLAY=DESC -(WO/1999/030745) DOTA-BIOTIN DERIVATIVES </ref>. The [[table of permselectivity for different substances]] contains examples. == Molecular formula == The [[empirical formula]] of a molecule is the '''simplest''' [[integer]] [[ratio]] of the [[chemical element]]s that constitute the compound. For example, in their pure forms, [[water]] is always composed of a 2:1 ratio of [[hydrogen]] to [[oxygen]], and ethyl [[alcohol]] or [[ethanol]] is always composed of [[carbon]], [[hydrogen]], and [[oxygen]] in a 2:6:1 ratio. However, this does not determine the kind of molecule uniquely - [[dimethyl ether]] has the same ratio as ethanol, for instance. Molecules with the same [[atom]]s in different arrangements are called [[isomer]]s. The empirical formula is often the same as the molecular formula but not always. For example the molecule [[acetylene]] has molecular formula C<sub>2</sub>H<sub>2</sub>, but the simplest integer ratio of elements is CH. The [[molecular formula]] reflects the exact number of atoms that compose a molecule. The [[molecular mass]] can be calculated from the chemical formula and is expressed in conventional [[atomic mass unit]]s equal to 1/12th of the mass of a neutral carbon-12 (<sup>12</sup>[[carbon|C]] [[isotope]]) atom. For [[network solid]]s, the term [[formula unit]] is used in [[stoichiometric]] calculations. == Molecular geometry == {{main|Molecular geometry}} Molecules have fixed [[mechanical equilibrium|equilibrium]] geometries&mdash;bond lengths and angles&mdash; about which they continuously oscillate through vibrational and rotational motions. A pure substance is composed of molecules with the same [[average]] geometrical structure. The chemical formula and the structure of a molecule are the two important factors that determine its properties, particularly its [[reactivity]]. Isomers share a chemical formula but normally have very different properties because of their different structures. [[Stereoisomer]]s, a particular type of isomers, may have very similar physico-chemical properties and at the same time very different [[biochemistry|biochemical]] activities. == Molecular spectroscopy == {{main|Spectroscopy}} '''Molecular spectroscopy''' deals with the response ([[frequency spectrum|spectrum]]) of molecules interacting with probing signals of known [[energy]] (or [[frequency]], according to [[Planck's constant|Planck's formula]]). [[Scattering theory]] provides the theoretical background for spectroscopy. The probing signal used in spectoore can be an [[electromagnetic wave]] or a beam of [[Elementary particle|particle]]s ([[electron]]s, [[positron]]s, etc.) The molecular response can consist of signal absorption ([[absorption spectroscopy]]), the emission of another signal ([[emission spectroscopy]]), fragmentation, or chemical changes. Spectroscopy is recognized as a powerful tool in investigating the [[microscopic]] properties of molecules, in particular their [[energy level]]s. In order to extract maximum microscopic information from experimental results, spectroscopy is often coupled with [[computational chemistry|chemical computations]]. == Theoretical aspects == The study of molecules by [[molecular physics]] and [[theoretical chemistry]] is largely based on [[quantum mechanic]]s and is essential for the understanding of the [[chemical bond]]. The simplest of molecules is the [[hydrogen molecule-ion]], H<sub>2</sub><sup>+</sup>, and the simplest of all the chemical bonds is the [[one-electron bond]]. H<sub>2</sub><sup>+</sup> is composed of two positively-charged [[proton]]s and one negatively-charged [[electron]] bound by [[photon]] exchange, which means that the [[Schrödinger equation]] for the system can be solved more easily due to the lack of electron–electron repulsion. With the development of fast digital computers, approximate solutions for more complicated molecules became possible and are one of the main aspects of [[computational chemistry]]. When trying to define rigorously whether an arrangement of atoms is "sufficiently stable" to be considered a molecule, IUPAC suggests that it "must correspond to a depression on the [[potential energy surface]] that is deep enough to confine at least one vibrational state".<ref name="iupac"/> This definition does not depend on the nature of the interaction between the atoms, but only on the strength of the interaction. In fact, it includes weakly-bound species that would not traditionally be considered molecules, such as the [[helium]] [[dimer]], He<sub>2</sub>, which has one vibrational [[bound state]] but is so loosely bound that it is only likely to be observed at very low temperatures. ==Etymology== According to [[Merriam-Webster]] and the [[Online Etymology Dictionary]], the word "molecule" derives from the [[Latin]] "[[Mole (unit)|moles]]" or small unit of mass. *'''Molecule''' (1794) - "extremely minute particle," from Fr. ''molécule'' (1678), from Mod.L. ''molecula'', dim. of L. moles "mass, barrier". A vague meaning at first; the vogue for the word (used until late 18th century only in Latin form) can be traced to the philosophy of [[Descartes]]. Most molecules are made up of multiple atoms; for example, a molecule of water is a combination of two [[hydrogen]] atoms and one [[oxygen]] atom. The term 'molecule' in gases has been used as a synonym for the fundamental particles of the gas, whatever their structure. This definition results in a few types of gases (for example inert elements that do not form compounds, such as [[neon]]), which has 'molecules' consisting of only a single atom.<ref>{{cite book | title=Comprehensive Inorganic Chemistry | last=Chandra | first=Sulekh | publisher=New Age Publishers | isbn=8122415121 }}</ref> == See also == * [[Molecular modelling]] * [[Covalent bond]] * [[Diatomic molecule]] * [[History of the molecule]] * [[Molecular geometry]] * [[Molecular Hamiltonian]] * [[Molecular orbital]] * [[Chemical polarity]] * For a list of molecules see the [[List of compounds]] * [[List of molecules in interstellar space]] ==References== <div class="references-small"> <!--See http://en.wikipedia.org/wiki/Wikipedia:Footnotes for an explanation of how to generate footnotes using the <ref(erences/)> tags--> <references/> </div> ==External links== *[http://www.chm.bris.ac.uk/motm/motm.htm Molecule of the Month] - School of Chemistry, University of Bristol {{particles}} {{Composition}} [[Category:Matter]] [[Category:Chemistry]] [[Category:Molecular physics| ]] [[Category:Molecules]] {{Link FA|lmo}} <!-- interwiki --> [[af:Molekuul]] [[als:Molekül]] [[ar:جزيء]] [[an:Molecula]] [[ast:Molécula]] [[az:Molekul]] [[bn:অণু]] [[zh-min-nan:Hun-chú]] [[be:Малекула]] [[bs:Molekula]] [[bg:Молекула]] [[ca:Molècula]] [[cs:Molekula]] [[cy:Moleciwl]] [[da:Molekyle]] [[de:Molekül]] [[dsb:Molekul]] [[et:Molekul]] [[el:Μόριο]] [[es:Molécula]] [[eo:Molekulo]] [[eu:Molekula]] [[fa:مولکول]] [[fo:Mýl]] [[fr:Molécule]] [[ga:Móilín]] [[gl:Molécula]] [[ko:분자]] [[hsb:Molekul]] [[hr:Molekula]] [[io:Molekulo]] [[id:Molekul]] [[is:Sameind]] [[it:Molecola]] [[he:מולקולה]] [[pam:Molecule]] [[kn:ಮಹತ್ಕಣ]] [[ka:მოლეკულა]] [[ku:Molekul]] [[la:Molecula]] [[lv:Molekula]] [[lt:Molekulė]] [[lmo:Mulécula]] [[hu:Molekula]] [[mk:Молекула]] [[ml:തന്മാത്ര (രസതന്ത്രം)]] [[mr:रेणू]] [[ms:Molekul]] [[nl:Molecuul]] [[ja:分子]] [[no:Molekyl]] [[nn:Molekyl]] [[nrm:Molétchule]] [[nov:Molekule]] [[oc:Molecula]] [[uz:Molekula]] [[nds:Molekül]] [[pl:Cząsteczka]] [[pt:Molécula]] [[ro:Moleculă]] [[qu:Iñuwa]] [[ru:Молекула]] [[sq:Molekula]] [[simple:Molecule]] [[sk:Molekula]] [[sl:Molekula]] [[sr:Молекул]] [[sh:Molekula]] [[su:Molekul]] [[fi:Molekyyli]] [[sv:Molekyl]] [[tl:Molekula]] [[ta:மூலக்கூறு]] [[th:โมเลกุล]] [[vi:Phân tử]] [[tr:Molekül]] [[uk:Молекула]] [[ur:سالمہ]] [[yi:מאלעקול]] [[zh-yue:分子]] [[zh:分子]]