See soorce fer Atom

{{fixscots|date=Januar 2021}}

{{Infobox atom}}
An '''atom''' is the smawest consteetuent unit o ordinary [[matter]] that haes the properties o a [[chemical element]].<ref>{{cite encyclopedia|title=Atom|encyclopedia=[[Compendium of Chemical Terminology|Compendium of Chemical Terminology (IUPAC Gold Book)]]|publisher=IUPAC|edition=2nd|url=http://goldbook.iupac.org/A00493.html|accessdate=2015-04-25}}</ref> Ivery [[solit]], [[liquid]], [[gas]], an [[plasma (physics)|plasma]] is componed o neutral or [[ionised]] atoms. Atoms are very smaw; teepical sizes are aroond 100&nbsp;[[picometre]]s (a ten-billiont o a metre, in the short scale).<ref name=Ghosh02>{{cite journal | author = Ghosh, D. C. |author2= Biswas, R. | title = Theoretical calculation of Absolute Radii of Atoms and Ions. Part 1. The Atomic Radii | journal = Int. J. Mol. Sci. | volume = 3 | pages = 87–113 | year = 2002 | doi=10.3390/i3020087| doi-access = free }}</ref>

Atoms [[Maiter swaw#The de Broglie hypothesis|are smaw eneuch]] that attemptin tae predict thair behaviour uisin clessical physics - as if thay war billiard baws, for ensaumple - gies noticeably incorrect predictions due tae [[quantum mechanics|quantum effects]]. Throu the development o physics, atomic models hae incorporatit [[#Further developments in quantum physics|quantum principles]] tae better expleen an predict the behaviour.

Ivery atom is componed o a [[atomic nucleus|nucleus]] an ane or mair [[electron]]s boond tae the nucleus. The nucleus is made o ane or mair [[proton]]s an teepically a seemilar nummer o [[neutron]]s. Protons an neutrons are cried [[nucleon]]s. Mair nor 99.94% o an atom's mass is in the nucleus. The protons hae a positive [[electric chairge]], the electrons hae a negative electric chairge, an the neutrons hae na electric chairge. If the nummer o protons an electrons are equal, that atom is electrically neutral. If an atom haes mair or fewer electrons nor protons, then it haes an oweraw negative or positive charge, respectively, an it is cried an [[ion]].

The electrons o an atom are attractit tae the protons in an atomic nucleus bi this [[electromagnetic force]]. The protons an neutrons in the nucleus are attractit tae ilk ither bi a different force, the [[nuclear force]], which is uisually stranger than the electromagnetic force repellin the positively charged protons frae ane anither. Unner certaint circumstances the repellin electromagnetic force becomes stranger nor the nuclear force, an nucleons can be ejectit frae the nucleus, leavin behind a different element: [[nuclear decay]] resultin in [[nuclear transmutation]].

The nummer o protons in the nucleus defines tae what [[chemical element]] the atom belangs: for ensaumple, aw [[copper]] atoms conteen 29 protons. The nummer o neutrons defines the [[isotope]] o the element.<ref name=leigh1990>{{cite book|editor=Leigh, G. J.|year=1990|title=International Union of Pure and Applied Chemistry, Commission on the Nomenclature of Inorganic Chemistry, [[Nomenclature of Organic Chemistry]] – Recommendations 1990|publisher=Blackwell Scientific Publications|isbn=0-08-022369-9|page=35|location=Oxford|quote=An atom is the smallest unit quantity of an element that is capable of existence whether alone or in chemical combination with other atoms of the same or other elements.}}</ref> The nummer o electrons influences the [[magnetic]] properties o an atom. Atoms can attach tae ane or mair ither atoms bi [[chemical bond]]s tae form [[chemical compoonds]] sic as [[molecule]]s. The abeelity o atoms tae associate an dissociate is responsible for maist o the physical chynges observed in naitur, an is the subject o the discipline o [[chemistry]].

==History o atomic theory==
===Auncient times===
The idea that matter is made up o discrete units is a very auld idea, appearin in mony auncient culturs sic as Greece an Indie. The wird "atom" wis creatit bi [[Auncient Greek filosofie|auncient Greek filosofers]]. Houiver, thir ideas war foondit in filosofical an theological raisonin raither nor evidence an experimentation. As a result, thair views on whit atoms leuk lik an hou thay behave war incorrect.

===1800s===
[[File:Daltons symbols.gif|right|thumb|Various atoms an molecules as depictit in [[John Dalton]]'s ''A New System of Chemical Philosophy'' (1808).]]
In the early 1800s, [[John Dalton]] uised the concept o atoms tae expleen why [[Chemical element|elements]] ayeweys react in ratios o smaw hale nummers (the [[law o multiple proportions]]). Dalton believed atomic theory coud expleen why watter absorbs different gases in different proportions an aw. For ensaumple, he foond that watter absorbs [[carbon dioxide]] faur better nor it absorbs [[nitrogen]].<ref name = "Dalton_1803_paper">Dalton, John. "[http://web.lemoyne.edu/~GIUNTA/dalton52.html On the Absorption of Gases by Water and Other Liquids]", in ''Memoirs of the Literary and Philosophical Society of Manchester''. 1803. Retrieved on August 29, 2007.</ref> Dalton hypothesized this wis due tae the differences atween the masses an configurations o the gases' respective pairticles, an carbon dioxide molecules (CO<sub>2</sub>) are hivier an lairger nor nitrogen molecules (N<sub>2</sub>). In 1827, [[Botany|botanist]] [[Robert Brown (Scots botanist frae Munross)|Robert Brown]] uised a microscope tae leuk at dist grains fleetin in watter an discovered that thay muived aboot erratically, a phenomenon that became kent as "[[Brownian motion]]". This wis thocht tae be caused bi watter molecules knockin the grains aboot. In 1905, [[Albert Einstein]] pruived the reality o thir molecules an thair motions bi producin the first [[Stateestical physics]] analysis o [[Brownian motion]].<ref name=adp322_8_549/><ref>{{cite book
|last=Mazo|first=Robert M.|year=2002
|title=Brownian Motion: Fluctuations, Dynamics, and Applications
|url=https://archive.org/details/brownianmotion00mazo|publisher=Oxford University Press|isbn=0-19-851567-7
|oclc=48753074|pages=[https://archive.org/details/brownianmotion00mazo/page/n11 1]–7}}
</ref><ref name=lee_hoon1995/> French physicist [[Jean Perrin]] uised Einstein's wark tae experimentally determine the mass an dimensions o atoms, thareby conclusively verifeein [[Dalton's atomic theory]].<ref name=e31_2_50/>

===Early 1900s===
The physicist [[J. J. Thomson]] meisurt the mass o cathode rays, shawin thay war made o pairticles, but war aroond 1800 times lichter nor the lichtest atom, [[hydrogen]]. Tharefore, thay war nae atoms, but a new pairticle, the first ''[[subatomic pairticle|subatomic]]'' pairticle tae be discovered, that he oreeginally cried "''corpuscle''" but wis later named ''electron'', efter pairticles postulatit bi [[George Johnstone Stoney]] in 1874. He shawed thay war identical tae pairticles gien off bi [[Photoelectric effect|photoelectric]] an radioactive materials an aw.<ref name="Thomson">{{cite journal|last=Thomson|first=J. J.|title=On bodies smaller than atoms|journal=The Popular Science Monthly|volume=|issue= |pages=323–335|publisher=Bonnier Corp.|location= |date=August 1901|url=https://books.google.com/?id=3CMDAAAAMBAJ&pg=PA323|doi= |id= |accessdate=2009-06-21}}</ref> It wis quickly recognised that thay are the pairticles that cairy [[electric current]]s in metal weirs, an cairy the negative electric chairge within atoms. Thomson wis gien the 1906 [[Nobel Prize in Physics]] for this wark. Sicweys he owerturned the belief that atoms are the indivrrsible, ultimate pairticles o matter.<ref name=nobel1096/> Thomson incorrectly postulatit that the law mass, negatively chairged electrons wra distributed ootthrou the atom in a uniform sea o positive chairge an aw.

In 1909, [[Hans Geiger]] an [[Ernest Marsden]], unner the direction o [[Ernest Rutherford]], bombardit a metal foil wi [[alpha pairticle]]s tae observe hou thay scaitert. Thay expectit aw the alpha pairticles tae pass straicht throu wi little deflection, acause Thomson's model said that the chairges in the atom are sae diffuise that thair electric fields coud nae affect the alpha pairticles muckle. Houiver, Geiger an Marsden spottit alpha pairticles bein deflectit bi angles greater nor 90°, that wis supposed tae be impossible accordin tae Thomson's model. Tae expleen this, Rutherford proponed that the positive charge o the atom is concentratit in a tottie nucleus at the centre o the atom.<ref name=pm21_669/> Rutherford compared his findins tae ane firin a 15-inch shell an it comin back tae hit the person wha fired it.<ref>{{cite web|title=The Gold Foil Experiment|url=http://myweb.usf.edu/~mhight/goldfoil.html|website=myweb.usf.edu|access-date=2017-08-02|archive-date=2016-11-19|archive-url=https://web.archive.org/web/20161119121837/http://myweb.usf.edu/~mhight/goldfoil.html|url-status=dead}}</ref>

While experimentin wi the products o [[radioactive decay]], in 1913 [[radiochemistry|radiochemist]] [[Frederick Soddy]] discovered that thare appeared tae be mair nor ane teep o atom at ilk poseetion on the periodic cairt.<ref name=npc1921/> The term [[isotope]] wis coined bi [[Margaret Todd (doctor)|Margaret Todd]] as a suitable name for different atoms that alang tae the same element. J.J. Thomson creatit a technique for separatin atom teeps throu his wark on ionised gases, that subsequently led tae the discovery o [[stable isotope]]s.<ref name=prsA_89_1_1913/>

In 1913 the physicist [[Niels Bohr]] proponed a model in that the electrons o an atom war assumed tae orbit the nucleus but coud anerly dae sae in a finite set o orbits, an coud jimp atween thir orbits anerly in discrete cheenges o energy correspondin tae absorption or radiation o a photon.<ref name=stern20050516/> This quantisation wis uised tae expleen why the electrons orbits are stable (gien that normally, chairges in acceleration, includin circular motion, lose kinetic energy that is emittit as electromagnetic radiation, see ''[[synchrotron radiation]]'') an why elements absorb an emit electromagnetic radiation in discrete spectra.<ref name=bohr19221211/> Later in the same year [[Henry Moseley]] providit addeetional experimental evidence in favour o [[Bohr model|Niels Bohr's theory]].

In 1924, [[Louis de Broglie]] proponed that aw pairticles behave tae an extent lik swaws. In 1926, [[Erwin Schrödinger]] uised this idea tae develop a mathematical model o the atom that descrived the electrons as three-dimensional [[swawform]]s raither nor pynt pairticles. The development o the [[mass spectrometry|mass spectrometer]] allaed the mass o atoms tae be meisurt wi increased accuracy. The device uises a magnet tae bend the trajectory o a beam o ions, an the amoont o deflection is determined bi the ratio o an atom's mass tae its chairge. The chemist [[Francis William Aston]] uised this instrument tae shaw that isotopes haed different masses. The [[atomic mass]] o thir isotopes varied bi integer amoonts, cried the [[hale nummer rule]].<ref name=pm39_6_449/> The explanation for thir different isotopes awaitit the discovery o the [[neutron]], an unchairged pairticle wi a mass seemilar tae the [[proton]], bi the physicist [[James Chadwick]] in 1932.

In 1938, the German chemist [[Otto Hahn]], a student o Rutherford, directit neutrons ontae uranium atoms expectin tae get [[transuranium element]]s. Insteid, his chemical experiments shawed [[barium]] as a product.<ref name=Bowden/><ref name=CHF/> A year later, [[Lise Meitner]] an her neffae [[Otto Frisch]] verifee'd that Hahn's result war the first experimental ''nuclear fission''.<ref name=nature143_3615_239/><ref name=schroeder/> In 1944, Hahn received the [[Nobel prize]] in chemistry. Despite Hahn's efforts, the contreibutions o Meitner an Frisch war nae recognised.<ref name=pt50_9_26/>

==Structur==
===Subatomic pairticles===
Tho the wird ''atom'' oreeginally denotit a pairticle that canna be cut intae smawer pairticles, in modren scienteefic uissage the atom is componed o various [[subatomic pairticle]]s. The constituent pairticles o an atom are the [[electron]], the [[proton]] an the [[neutron]]; aw three are [[fermion]]s. Houiver, the [[hydrogen|hydrogen-1]] atom haes na neutrons an the [[hydron (chemistry)|hydron ion]] haes na electrons.

The electron is bi faur the least massive o thir pairticles at {{val|9.11|e=-31|u=kg}}, wi a negative [[Electric chairge|electrical chairge]] an a size that is too smaw tae be meisurt uisin available techniques.<ref>{{cite book|last=Demtröder|first=Wolfgang|year=2002|title=Atoms, Molecules and Photons: An Introduction to Atomic- Molecular- and Quantum Physics|publisher=Springer|edition=1st|isbn=3-540-20631-0|oclc=181435713|pages=39–42}}</ref> Protons hae a positive chairge an a mass 1,836 times that o the electron, at {{val|1.6726|e=-27|u=kg}}. The nummer o protons in an atom is cried its [[atomic nummer]]. Neutrons hae na electrical chairge an hae a free mass o 1,839 times the mass o the electron,<ref>{{cite book|last=Woan|first=Graham|year=2000|title=The Cambridge Handbook of Physics|url=https://archive.org/details/cambridgehandboo00woan_344|publisher=Cambridge University Press|isbn=0-521-57507-9|oclc=224032426|page=[https://archive.org/details/cambridgehandboo00woan_344/page/n15 8]}}</ref> or {{val|1.6929|e=-27|u=kg}}, the hiviest o the three constituent pairticles, but it can be reduced bi the [[nuclear bindin energy]].

Baith protons an neutrons are composite pairticles componed o [[elementary pairticle]]s cried [[quark]]s. Thare are twa teeps o quarks in atoms, ilk haein a fractional electric chairge. Protons are componed o twa [[up quark]]s (ilk wi chairge +{{sfrac|2|3}}) an ane [[doun quark]] (wi a chairge o −{{sfrac|1|3}}). Neutrons conseest o ane up quark an twa doun quarks. This distinction accoonts for the difference in mass an chairge atween the twa pairticles.<ref name=pdg2002/><ref name=schombert2006/> The quarks are held thegither bi the [[strang interaction]] (or strang force), that is mediatit bi [[gluon]]s.

===Nucleus===
[[File:Wpdms physics proton proton chain 1.svg|right|thumb|Illustration o a nuclear fusion process that forms a deuterium nucleus, conseestin o a proton an a neutron, frae twa protons. A [[positron]] (e<sup>+</sup>)—an [[antimaiter]] electron—is emitted alang wi an electron [[neutrino]].]]
Aw the boond protons an neutrons in an atom mak up a tottie [[atomic nucleus]], an are collectively cried [[nucleon]]s. The radius o a nucleus is approximately equal tae 1.07&nbsp;{{radic|''A''|3}}&nbsp;[[femtometre|fm]], whaur ''A'' is the tot nummer o nucleons.<ref>{{cite book|last=Jevremovic|first=Tatjana|year=2005|title=Nuclear Principles in Engineering|url=https://archive.org/details/nuclearprinciple00jevr_745|publisher=Springer|isbn=0-387-23284-2|oclc=228384008|page=[https://archive.org/details/nuclearprinciple00jevr_745/page/n75 63]}}</ref> This is muckle smawer nor the radius o the atom, that is on the order o 10<sup>5</sup>&nbsp;fm. The nucleons are boond thegither bi a short-ranged attractive potential cried the [[residual strang force]]. At distances smawer nor 2.5 fm this force is muckle mair pouerfu nor the [[electrostatic force]] that causes positively chairged protons tae repel ilk ither.<ref>{{cite book|last=Pfeffer|first=Jeremy I.|last2=Nir|first2=Shlomo|year=2000|title=Modern Physics: An Introductory Text|publisher=Imperial College Press|isbn=1-86094-250-4|oclc=45900880|pages=330–336}}</ref> The proton, the electron, an the neutron are clessifee'd as [[fermion]]s.

===Electron clood===
The electrons in an atom are attractit tae the protons in the nucleus bi the [[electromagnetic force]]. This force binds the electrons inside an [[electrostatic]] [[potential wall]] surroondin the smawer nucleus, that means that an freemit soorce o energy is needit for the electron tae escape. The closer an electron is tae the nucleus, the greater the attractive force. Hence electrons boond near the centre o the potential wall require mair energy tae escape nor thae at greater separations.

==Properties==
Bi defineetion, ony twa atoms wi an identical nummer o ''protons'' in thair nuclei alang tae the same [[chemical element]]. Atoms wi equal nummers o protons but a different nummer o ''neutrons'' are different isotopes o the same element. For ensaumple, aw hydrogen atoms admit exactly ane proton, but isotopes exist wi no neutrons ([[hydrogen-1]], bi faur the maist common form,<ref name=matis2000/> cried protium an aw), ane neutron ([[deuterium]]), twa neutrons ([[tritium]]) an [[isotopes o hydrogen|mair nor twa neutrons]].

Aboot 339 nuclides occur naiturally on [[Yird]],<ref name=lidsay20000730/> o that 254 (aboot 75%) hae nae been observed tae decay, an are referred tae as "[[stable isotope]]s". Houiver, anerly 90 o thir nuclides are stable tae aw decay, even [[leet o nuclides|in theory]]. Anither 164 (bringin the tot tae 254) hae nae been observed tae decay, even tho in theory it is energetically possible.

The lairge majority o an atom's mass comes frae the protons an neutrons that mak it up. The tot nummer o thir pairticles (cried "nucleons") in a gien atom is cried the [[mass nummer]]. It is a positive integer an dimensionless (insteid o haein dimension o mass), acause it expresses a coont. An ensaumple o uise o a mass nummer is "carbon-12," that haes 12 nucleons (sax protons an sax neutrons). The actual [[Invariant mass|mass o an atom at rest]] is eften expressed uisin the [[Atomic mass unit|unifee'd atomic mass unit]] (u), cried dalton (Da) an aw. As even the maist massive atoms are faur too licht tae wirk wi directly, chemists insteid uise the unit o [[Mole (unit)|moles]]. Ane mole o atoms o ony element ayeweys haes the same nummer o atoms (aboot [[Avogadro constant|{{val|6.022|e=23}}]]). This nummer wis chosen sae that if an element haes an atomic mass o 1&nbsp;u, a mole o atoms o that element haes a mass close tae ane gram.

Atoms lack a well-defined ooter boondary, sae thair dimensions are uisually descrived in terms o an [[atomic radius]]. This is a meisur o the distance oot tae that the electron clood extends frae the nucleus.<ref name="Ghosh02"/> Whan subjectit tae fremmit forces, lik [[electrical field]]s, the shape o an atom mey deviate frae [[spherical symmetry]]. The deformation depends on the field magnitude an the orbital teep o ooter shell electrons, as shawn bi [[group theory|group-theoretical]] conseederations.

Atomic dimensions are thoosands o times smawer nor the swawlenths o [[licht]] (400–700&nbsp;[[nanometre|nm]]) sae thay canna be viewed uising an [[optical microscope]]. Houever, individual atoms can be observed uisin a [[scannin tunnelin microscope]]. Tae veesualise the size o the atom, consider that a teepical human hair is aboot 1&nbsp;million carbon atoms in weenth.<ref name=osu2007/> A single drap o watter conteens aboot 2&nbsp;[[sextillion]] ({{val|2|e=21}}) atoms o oxygen, an twice the nummer o hydrogen atoms.<ref>{{cite book
|last=Padilla|first=Michael J.
|author2=Miaoulis, Ioannis|author3= Cyr, Martha|year = 2002
|title = Prentice Hall Science Explorer: Chemical Building Blocks
|publisher = Prentice-Hall, Inc.
|location = Upper Saddle River, New Jersey USA
|isbn = 0-13-054091-9
|oclc=47925884|page=32
|quote=There are 2,000,000,000,000,000,000,000 (that's 2&nbsp;sextillion) atoms of oxygen in one drop of water—and twice as many atoms of hydrogen.}}</ref>

Ivery element haes ane or mair isotopes that hae unstable nuclei that are subject tae radioactive decay, causin the nucleus tae emit pairticles or electromagnetic radiation. Radioactivity can occur whan the radius o a nucleus is lairge compared wi the radius o the strang force, that anerly acts ower distances on the order o 1&nbsp;fm.<ref name=splung/>

The maist common forms o radioactive decay are:<ref>{{cite book
|last=L'Annunziata<!-- Note: the single quote mark before the name is correct. -->
|first=Michael F.
|year=2003|title=Handbook of Radioactivity Analysis
|url=https://archive.org/details/handbookradioact00lann|publisher=Academic Press|isbn=0-12-436603-1
|oclc=16212955|pages=[https://archive.org/details/handbookradioact00lann/page/n22 3]–56}}</ref><ref name=firestone20000522/>
* [[Alpha decay]]: this process is caused whan the nucleus emits an alpha pairticle, that is a helium nucleus conseestin o twa protons an twa neutrons. The result o the emission is a new element wi a lawer [[atomic nummer]].
* [[Beta decay]] (an [[electron captur]]): thir processes are regulatit bi the [[waik force]], an result frae a transformation o a neutron intae a proton, or a proton intae a neutron. The neutron tae proton transeetion is accompanied bi the emission o an electron an an [[antineutrino]], while proton tae neutron transeetion (except in electron captur) causes the emission o a [[positron]] an a [[neutrino]]. The electron or positron emissions are cried beta pairticles. Beta decay aither increases or decreases the atomic nummer o the nucleus bi ane. Electron captur is mair common nor positron emission, acause it requires less energy. In this teep o decay, an electron is absorbed bi the nucleus, raither nor a positron emittit frae the nucleus. A neutrino is still emittit in this process, an a proton cheenges tae a neutron.
* [[Gamma decay]]: this process results frae a cheenge in the energy level o the nucleus tae a lawer state, resultin in the emission o electromagnetic radiation. The excitit state o a nucleus which results in gamma emission uisually occurs follaein the emission o an alpha or a beta pairticle. Sicwweys, gamma decay uisually follaes alpha or beta decay.

Elementar pairticles possess an intrinsic quantum mechanical property kent as [[Spin (physics)|spin]]. This is analogous tae the [[angular momentum]] o an object that is spinnin aroond its [[centre o mass]], awtho strictly speakin thir pairticles are believed tae be pynt-lik an canna be said tae be rotatin. Spin is meisurt in units o the reduced [[Planck constant]] (ħ), wi electrons, protons an neutrons aw haein spin ½&nbsp;ħ, or "spin-½".

At temperaturs close tae [[absolute zero]], atoms can form a [[Bose–Einstein condensate]], at which pynt quantum mechanical effects, that are normally anerly observed at the atomic scale,becom apparent on a macroscopic scale.<ref>{{cite book
|last=Myers|first=Richard|year=2003
|title=The Basics of Chemistry|url=https://archive.org/details/basicsofchemistr0000myer|publisher=Greenwood Press
|isbn=0-313-31664-3
|oclc=50164580|page=[https://archive.org/details/basicsofchemistr0000myer/page/85 85]}}</ref><ref name=nist_bec/> This super-cuiled collection o atoms
then behaves as a single [[super atom]], that mey allae fundamental checks o quantum mechanical behaviour.<ref name=colton_fyffe1999/>

==Identification==
The [[scannin tunnelin microscope]] is a device for viewin surfaces at the atomic level. It uises the [[quantum tunnelin]] phenomenon, that allaes pairticles tae pass throu a barrier that wad normally be insurmoontable. Electrons tunnel throu the vacuum atween twa planar metal electrodes, on ilk o that is an [[adsorb]]ed atom, providin a tunnelin-current density that can be meisurt. Scannin ane atom (taken as the tip) as it muives past the ither (the saumple) permits plottin o tip displacement versus lateral separation for a constant current. The calculation shaws the extent tae that scannin-tunnelin-microscope eemages o an individual atom are veesible. It confirms that for law bias, the microscope eemages the space-averaged dimensions o the electron orbitals athort closely packed energy levels—the [[Fermi level]] [[local density o states]].<ref name=jacox1997/><ref name=nf_physics1986/>

==References==
{{reflist|colwidth=30em|refs=
<!--Unused ref<ref name=leigh1990>{{cite book|editor=Leigh, G. J.|year=1990|title=International Union of Pure and Applied Chemistry, Commission on the Nomenclature of Inorganic Chemistry, [[Nomenclature of Organic Chemistry]] – Recommendations 1990|publisher=Blackwell Scientific Publications|isbn=0-08-022369-9|page=35|location=Oxford|quote=An atom is the smallest unit quantity of an element that is capable of existence whether alone or in chemical combination with other atoms of the same or other elements.}}</ref>-->

<!--ref name=slac_20090615>{{cite web|date=15 June 2009|title=Radioactive Decays|url=http://www2.slac.stanford.edu/vvc/theory/nuclearstability.html|publisher=[[Stanford Linear Accelerator Center]]|accessdate=4 July 2009| archiveurl= https://web.archive.org/web/20090607115741/http://www2.slac.stanford.edu/vvc/theory/nuclearstability.html| archivedate= 7 June 2009 | deadurl= no}}</ref-->

<ref name=adp322_8_549>{{cite journal|last=Einstein|first=Albert|year=1905|title=Über die von der molekularkinetischen Theorie der Wärme geforderte Bewegung von in ruhenden Flüssigkeiten suspendierten Teilchen|journal=[[Annalen der Physik]]|volume=322|issue=8|pages=549–560|language=German|url=http://www.zbp.univie.ac.at/dokumente/einstein2.pdf|format=PDF|doi=10.1002/andp.19053220806|accessdate=4 February 2007|bibcode=1905AnP...322..549E|archive-date=2007-07-18|archive-url=https://web.archive.org/web/20070718202731/http://www.zbp.univie.ac.at/dokumente/einstein2.pdf|url-status=dead}}</ref>

<ref name=lee_hoon1995>{{cite web|last=Lee|first=Y.K.|year=1995|author2=Hoon, K.|title=Brownian Motion|url=http://www.doc.ic.ac.uk/~nd/surprise_95/journal/vol4/ykl/report.html|publisher=[[Imperial College]]|accessdate=18 December 2007|archiveurl=https://web.archive.org/web/20071218061408/http://www.doc.ic.ac.uk/~nd/surprise_95/journal/vol4/ykl/report.html|archivedate=2007-12-18|deadurl=no|url-status=dead}}</ref>

<ref name=e31_2_50>{{cite journal|last=Patterson|first=G.|year=2007 |title=Jean Perrin and the triumph of the atomic doctrine|url=https://archive.org/details/sim_endeavour_2007-06_31_2/page/50|journal=[[Endeavour (journal)|Endeavour]]|volume=31|issue=2|pages=50–53|doi=10.1016/j.endeavour.2007.05.003|pmid=17602746}}</ref>

<ref name=nobel1096>{{cite web|year=1906|title=J.J. Thomson|url=http://nobelprize.org/nobel_prizes/physics/laureates/1906/thomson-bio.html|publisher=[[Nobel Foundation]]|accessdate=20 December 2007}}</ref>

<ref name=pm21_669>{{cite journal|last=Rutherford|first=E.|title=The Scattering of α and β Particles by Matter and the Structure of the Atom|url=http://users.uoa.gr/~pjioannou/mech1/READING/structureatom.pdf|journal=[[Philosophical Magazine]]|year=1911|volume=21|pages=669–88|doi=10.1080/14786440508637080|issue=125}}</ref>

<ref name=npc1921>{{cite web|url=http://nobelprize.org/nobel_prizes/chemistry/laureates/1921/soddy-bio.html|title=Frederick Soddy, The Nobel Prize in Chemistry 1921 |publisher=[[Nobel Foundation]]|accessdate=18 January 2008}}</ref>

<ref name=prsA_89_1_1913>{{cite journal|doi=10.1098/rspa.1913.0057|last=Thomson|first=Joseph John|title=Rays of positive electricity|url=http://web.lemoyne.edu/~giunta/canal.html|series=A|journal=[[Proceedings of the Royal Society]]|year=1913|volume=89|issue=607|pages=1–20|bibcode = 1913RSPSA..89....1T |doi-access=free}}</ref>

<ref name=stern20050516>{{cite web|last=Stern|first=David P.|date=16 May 2005|title=The Atomic Nucleus and Bohr's Early Model of the Atom|url=http://www-spof.gsfc.nasa.gov/stargaze/Q5.htm|publisher=[[NASA]]/[[Goddard Space Flight Center]]|accessdate=20 December 2007|archive-date=2007-08-20|archive-url=https://web.archive.org/web/20070820084047/http://www-spof.gsfc.nasa.gov/stargaze/Q5.htm|url-status=dead}}</ref>

<ref name=bohr19221211>{{cite web|last=Bohr|first=Niels|date=11 December 1922|title=Niels Bohr, The Nobel Prize in Physics 1922, Nobel Lecture|url=http://nobelprize.org/nobel_prizes/physics/laureates/1922/bohr-lecture.html|publisher=[[Nobel Foundation]]|accessdate=16 February 2008}}</ref>

<ref name=pm39_6_449>{{cite journal|last=Aston|first=Francis W.|year=1920|title=The constitution of atmospheric neon|journal=[[Philosophical Magazine]]|volume=39|issue=6|pages=449–55|doi=10.1080/14786440408636058}}</ref>

<ref name="CHF">{{cite web|title=Otto Hahn, Lise Meitner, and Fritz Strassmann|url=https://www.chemheritage.org/historical-profile/otto-hahn-lise-meitner-and-fritz-strassmann|website=Chemical Heritage Foundation|accessdate=27 October 2016}}</ref>

<ref name=Bowden>{{cite book|last1=Bowden|first1=Mary Ellen|title=Chemical achievers : the human face of the chemical sciences|url=https://archive.org/details/chemicalachiever0000bowd|date=1997|publisher=Chemical Heritage Foundation|location=Philadelphia, PA|isbn=9780941901123|chapter=Otto Hahn, Lise Meitner, and Fritz Strassmann|pages=[https://archive.org/details/chemicalachiever0000bowd/page/76 76]–80, 125}}</ref>

<ref name=nature143_3615_239>{{cite journal |last=Meitner|first=Lise|last2=Frisch|first2=Otto Robert|year=1939|title=Disintegration of uranium by neutrons: a new type of nuclear reaction|journal=[[Nature (journal)|Nature]]|volume=143 |issue=3615 |pages=239–240 |doi=10.1038/143239a0 |bibcode = 1939Natur.143..239M }}</ref>

<ref name=schroeder>{{cite web|last=Schroeder|first=M.|title=Lise Meitner – Zur 125. Wiederkehr Ihres Geburtstages|url=http://www.physik3.gwdg.de/~mrs/Vortraege/Lise_Meitner-Vortrag-20031106/|language=German|accessdate=4 June 2009|archive-date=2011-07-19|archive-url=https://web.archive.org/web/20110719034227/http://www.physik3.gwdg.de/~mrs/Vortraege/Lise_Meitner-Vortrag-20031106/|url-status=dead}}</ref>

<ref name=pt50_9_26>{{cite journal|last=Crawford |first=E.| year=1997|title=A Nobel tale of postwar injustice|url=https://www.researchgate.net/publication/260861491_A_nobel_tale_of_postwar_injustice|journal=[[Physics Today]]|volume=50|issue=9|pages=26–32|doi=10.1063/1.881933|last2=Sime|first2=Ruth Lewin|last3=Walker|first3=Mark |bibcode = 1997PhT....50i..26C }}</ref>

<ref name=pdg2002>{{cite web|author=Particle Data Group|year=2002|url=http://www.particleadventure.org/|title=The Particle Adventure|publisher=Lawrence Berkeley Laboratory|accessdate=3 January 2007| archiveurl= https://web.archive.org/web/20070104075936/http://www.particleadventure.org/| archivedate= 4 January 2007 <!--DASHBot-->| deadurl= no}}</ref>

<ref name=schombert2006>{{cite web|first=James|last=Schombert|date=18 April 2006|url=http://abyss.uoregon.edu/~js/ast123/lectures/lec07.html|title=Elementary Particles|publisher=University of Oregon|accessdate=3 January 2007|archive-date=2011-08-30|archive-url=https://web.archive.org/web/20110830212645/http://abyss.uoregon.edu/~js/ast123/lectures/lec07.html|url-status=dead}}</ref>

<ref name=matis2000>{{cite web|last=Matis|first=Howard S.|date=9 August 2000|url=http://www.lbl.gov/abc/wallchart/chapters/02/3.html|title=The Isotopes of Hydrogen|work=Guide to the Nuclear Wall Chart|publisher=Lawrence Berkeley National Lab|accessdate=21 December 2007| archiveurl= https://web.archive.org/web/20071218153548/http://www.lbl.gov/abc/wallchart/chapters/02/3.html| archivedate= 18 December 2007 <!--DASHBot-->| deadurl= no}}</ref>

<ref name=lidsay20000730>{{cite web|last=Lindsay|first=Don|date=30 July 2000|url=http://www.don-lindsay-archive.org/creation/isotope_list.html|title=Radioactives Missing From The Earth|publisher=Don Lindsay Archive|accessdate=23 May 2007| archiveurl= https://web.archive.org/web/20070428225550/http://www.don-lindsay-archive.org/creation/isotope_list.html| archivedate= 28 April 2007 <!--DASHBot-->| deadurl= no}}</ref>

<!--ref name=adp5f_3_133>{{cite journal|last = [[Bethe]]|first = H.|title=Termaufspaltung in Kristallen|journal=[[Annalen der Physik]] |year=1929|volume=395 |issue = 2 |pages=133–208|bibcode = 1929AnP...395..133B|doi = 10.1002/andp.19293950202}}</ref-->

<!--ref name=pssb245_9_1858>{{cite journal
|last = Birkholz|first = M.|author2=Rudert, R.
|title=Interatomic distances in pyrite-structure disulfides – a case for ellipsoidal modeling of sulfur ions
|journal=Physica Status Solidi (b)
|year=2008|volume=245
|issue=9|pages=1858–1864
|url=http://www.mariobirkholz.de/pssb2008.pdf
|doi=10.1002/pssb.200879532|bibcode = 2008PSSBR.245.1858B }}</ref-->

<ref name=osu2007>{{cite web |author=Staff|year=2007
|url=http://oregonstate.edu/terra/2007/02/small-miracles/
|title=Small Miracles: Harnessing nanotechnology
|publisher=Oregon State University |accessdate=7 January 2007}}—describes the width of a human hair as {{val|e=5|u=nm}} and 10 carbon atoms as spanning 1&nbsp;nm.</ref>

<ref name=splung>{{cite web |url=http://www.splung.com/content/sid/5/page/radioactivity |title=Radioactivity |publisher=Splung.com |accessdate=19 December 2007| archiveurl= https://web.archive.org/web/20071204135150/http://www.splung.com/content/sid/5/page/radioactivity| archivedate= 4 December 2007 <!--DASHBot-->| deadurl= no}}</ref>

<ref name=firestone20000522>{{cite web |last=Firestone |first=Richard B. |date=22 May 2000 |url=http://isotopes.lbl.gov/education/decmode.html |title=Radioactive Decay Modes |publisher=Berkeley Laboratory |accessdate=7 January 2007 |deadurl=yes |archiveurl=https://web.archive.org/web/20060929111801/http://isotopes.lbl.gov/education/decmode.html |archivedate=29 September 2006 }} {{Webarchive|url=https://web.archive.org/web/20060929111801/http://isotopes.lbl.gov/education/decmode.html |date=2006-09-29 }}</ref>

<ref name=nist_bec>{{cite news |author=Staff|date=9 October 2001 |title=Bose-Einstein Condensate: A New Form of Matter |publisher=National Institute of Standards and Technology |url=https://www.nist.gov/public_affairs/releases/bec_background.cfm |accessdate=16 January 2008| archiveurl= https://web.archive.org/web/20080103192918/https://www.nist.gov/public_affairs/releases/BEC_background.htm| archivedate= 3 January 2008 <!--DASHBot-->| deadurl= no}}</ref>

<ref name=colton_fyffe1999>{{cite web |last=Colton |first=Imogen |author2=Fyffe, Jeanette |date=3 February 1999 |url=http://www.ph.unimelb.edu.au/~ywong/poster/articles/bec.html |title=Super Atoms from Bose-Einstein Condensation |publisher=The University of Melbourne |accessdate=6 February 2008 |archiveurl=https://web.archive.org/web/20070829200820/http://www.ph.unimelb.edu.au/~ywong/poster/articles/bec.html |archivedate=29 August 2007 }} {{Webarchive|url=https://web.archive.org/web/20070829200820/http://www.ph.unimelb.edu.au/~ywong/poster/articles/bec.html |date=2007-08-29 }}</ref>

<ref name=jacox1997>{{cite web |last=Jacox|first=Marilyn|author2=Gadzuk, J. William |url=http://physics.nist.gov/GenInt/STM/stm.html |title=Scanning Tunneling Microscope |publisher=National Institute of Standards and Technology |date=November 1997|accessdate=11 January 2008 | archiveurl= https://web.archive.org/web/20080107133132/http://physics.nist.gov/GenInt/STM/stm.html| archivedate= 7 January 2008 <!--DASHBot-->| deadurl= no}}</ref>

<ref name=nf_physics1986>{{cite web |url=http://nobelprize.org/nobel_prizes/physics/laureates/1986/index.html |title=The Nobel Prize in Physics 1986 |publisher=The Nobel Foundation |accessdate=11 January 2008}}—in particular, see the Nobel lecture by G. Binnig and H. Rohrer.</ref>

}}

{{Commonscat|Atoms}}

[[Category:Atoms| ]]
[[Category:Concepts in physics]]
[[Category:Chemistry]]


{{Stub/Scieence}}