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{{Short description|Group of low-reactive, gaseous chemical elements}}
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{{Use dmy dates|date=February 2021}}
{{Infobox periodic table group
| title       = Noble gases
| group number= 18
| trivial name= noble gases
| by element  = helium group ''or''<br/>neon group
| CAS         = VIIIA
| old IUPAC   = 0
| mark        = He,Ne,Ar,Kr,Xe,Rn,Og
| left        = [[halogen]]s
| right       = [[alkali metal]]s}}
{| class="floatright"
! colspan=2 style="text-align:left;" | ↓&nbsp;<small>[[Period (periodic table)|Period]]</small>
|-
! [[Period 1 element|1]]
| {{element cell image|2|Helium|He| |Gas|Noble gases|Primordial|legend=|image=Helium discharge tube.jpg|image caption=Helium discharge tube}}
|-
! [[Period 2 element|2]]
| {{element cell image|10|Neon|Ne| |Gas|Noble gases|Primordial|legend=|image=Neon discharge tube.jpg|image caption=Neon discharge tube}}
|-
! [[Period 3 element|3]]
| {{element cell image|18|Argon|Ar| |Gas|Noble gases|Primordial|legend=|image=Argon discharge tube.jpg|image caption=Argon discharge tube}}
|-
! [[Period 4 element|4]]
| {{element cell image|36|Krypton|Kr| |Gas|Noble gases|Primordial|legend=|image=Krypton discharge tube.jpg|image caption=Krypton discharge tube}}
|-
! [[Period 5 element|5]]
| {{element cell image|54|Xenon|Xe| |Gas|Noble gases|Primordial|legend=|image=Xenon discharge tube.jpg|image caption=Xenon discharge tube}}
|-
! [[Period 6 element|6]]
| {{element cell image|86|Radon|Rn| |Gas|Noble gases|From decay|legend=|image=}}<!-- non-free image removed-->
|-
! [[Period 7 element|7]]
| {{element cell image|118|Oganesson|Og| |unknown phase|Noble gases|Synthetic|legend=|image=}}
|-
| colspan="2"|
----
''Legend''
{| style="text-align:center; border:0; margin: 0 auto;"
|-
| style="border:{{element color|Primordial}}; background:{{element color|table mark}}" | [[primordial element]]
|-
| style="border:{{element color|from decay}}; padding:0 2px; background:{{element color|table mark}}" | [[radioactive decay|element by radioactive decay]]
|-
| style="border:{{element color|Synthetic}}; background:{{Element color|table mark}};" | [[Synthetic element|synthetic]]
|}
|}

The '''noble gases''' (historically the '''inert gases''', sometimes referred to as '''aerogens'''<ref>{{cite journal |last1=Bauzá |first1=Antonio |last2=Frontera |first2=Antonio |date=2015 |title=Aerogen Bonding Interaction: A New Supramolecular Force? |journal=Angewandte Chemie International Edition |volume=54 |issue=25 |pages=7340–3 |doi=10.1002/anie.201502571|pmid=25950423 }}</ref>) are the members of [[Group (periodic table)|group]] 18 of the [[periodic table]]: [[helium]] (He), [[neon]] (Ne), [[argon]] (Ar), [[krypton]] (Kr), [[xenon]] (Xe), [[radon]] (Rn) and, in some cases, [[oganesson]] (Og). Under [[Standard temperature and pressure|standard conditions]], the first six of these [[Chemical element|elements]] are odorless, colorless, [[monatomic]] gases with very low [[chemical reactivity]] and [[cryogenics|cryogenic]] boiling points. The properties of oganesson are uncertain.

The [[intermolecular force]] between noble gas atoms is the very weak [[London dispersion force]], so their boiling points are all cryogenic, below {{convert|165|K|°C °F}}.<ref>{{Cite web |date=2023-11-28 |title=Xenon {{!}} Definition, Properties, Atomic Mass, Compounds, & Facts |url=https://www.britannica.com/science/xenon |access-date=2024-01-12 |website=Britannica |language=en}}</ref>

The noble gases' [[Chemically inert|inertness]], or tendency not to [[Chemical reaction|react]] with other [[chemical substance]]s, results from their [[electron configuration]]: their [[Electron shell|outer shell]] of [[valence electron]]s is "full", giving them little tendency to participate in [[chemical reaction]]s. Only a few hundred [[noble gas compound]]s are known to exist. The inertness of noble gases makes them useful whenever chemical reactions are unwanted. For example, argon is used as a [[shielding gas]] in [[welding]] and as a filler gas in [[incandescent light bulb]]s. Helium is used to provide buoyancy in [[blimp]]s and [[gas balloon|balloons]]. Helium and neon are also used as [[refrigerant]]s due to their low [[boiling point]]s. [[Manufacturing|Industrial]] quantities of the noble gases, except for radon, are obtained by separating them from [[air]] using the methods of [[liquefaction of gases]] and [[fractional distillation]]. Helium is also a byproduct of the mining of [[natural gas]]. Radon is usually isolated from the [[radioactive decay]] of dissolved [[radium]], [[thorium]], or [[uranium]] compounds.

The seventh member of group 18 is oganesson, an [[radioactive decay|unstable]] [[synthetic element]] whose chemistry is still uncertain because only five very short-lived atoms (t<sub>1/2</sub> = 0.69 ms) have ever been synthesized ({{as of|lc=y|2020}}<ref name="smits2020"/>). [[IUPAC]] uses the term "noble gas" interchangeably with "group 18" and thus includes oganesson;<ref name=Koppenol>{{cite journal |last= Koppenol|first=W.|date= 2016|title=How to name new chemical elements|journal=Pure and Applied Chemistry |publisher=DeGruyter |doi=10.1515/pac-2015-0802|hdl=10045/55935|s2cid=102245448 |s2cid-access=free |url=http://rua.ua.es/dspace/bitstream/10045/55935/1/2016_Koppenol_etal_PureApplChem.pdf|hdl-access=free |url-status=live |archive-url=https://web.archive.org/web/20231218023522/https://rua.ua.es/dspace/bitstream/10045/55935/1/2016_Koppenol_etal_PureApplChem.pdf |archive-date= Dec 18, 2023 }}</ref> however, due to [[relativistic quantum chemistry|relativistic effects]], oganesson is predicted to be a [[solid]] under standard conditions and reactive enough not to qualify functionally as "noble".<ref name="smits2020">{{cite journal |last1=Smits |first1=Odile R. |last2=Mewes |first2=Jan-Michael |last3=Jerabek |first3=Paul |last4=Schwerdtfeger |first4=Peter |date=2020 |title=Oganesson: A Noble Gas Element That Is Neither Noble Nor a Gas |journal=Angewandte Chemie International Edition |volume=59 |issue=52 |pages=23636–23640 |doi=10.1002/anie.202011976 |doi-access=free |pmid=32959952 |pmc=7814676 }}</ref>

==History==
''Noble gas'' is translated from the [[German language|German]] noun {{lang|de|Edelgas}}, first used in 1900 by [[Hugo Erdmann]]<ref>{{cite journal|journal=[[Science (journal)|Science]]|year=1901|volume=13|pages=268–270|last=Renouf|first=Edward|title=Noble gases|doi=10.1126/science.13.320.268|issue=320|bibcode= 1901Sci....13..268R |s2cid=34534533|url=https://archive.org/details/lehrbuchderanor01erdmgoog/page/78/mode/2up}}</ref> to indicate their extremely low level of reactivity. The name makes an analogy to the term "[[noble metal]]s", which also have low reactivity. The noble gases have also been referred to as ''[[inert gas]]es'', but this label is deprecated as many [[noble gas compound]]s are now known.<ref>{{harvnb|Ozima|2002|p=30}}</ref> ''Rare gases'' is another term that was used,<ref>{{harvnb|Ozima|2002|p=4}}</ref> but this is also inaccurate because [[argon]] forms a fairly considerable part (0.94% by volume, 1.3% by mass) of the [[Earth's atmosphere]] due to decay of radioactive [[potassium-40]].<ref>{{cite encyclopedia|encyclopedia=[[Encyclopædia Britannica]]|year=2008|title=argon|url=https://www.britannica.com/eb/article-9009382/argon}}</ref>
[[File:Helium spectrum.jpg|thumb|left|300px|Helium was first detected in the Sun due to its characteristic [[spectral line]]s.|alt=A line spectrum chart of the visible spectrum showing sharp lines on top.]]

[[Pierre Janssen]] and [[Joseph Norman Lockyer]] had discovered a new element on 18 August 1868 while looking at the [[chromosphere]] of the [[Sun]], and named it [[helium]] after the Greek word for the Sun, {{lang|grc|ἥλιος}} ({{lang|grc-Latn|hḗlios}}).<ref>''Oxford English Dictionary'' (1989), s.v. "helium". Retrieved 16 December 2006, from Oxford English Dictionary Online. Also, from quotation there: Thomson, W. (1872). ''Rep. Brit. Assoc.'' xcix: "Frankland and Lockyer find the yellow prominences to give a very decided bright line not far from D, but hitherto not identified with any terrestrial flame. It seems to indicate a new substance, which they propose to call Helium."</ref> No chemical analysis was possible at the time, but helium was later found to be a noble gas. Before them, in 1784, the English chemist and physicist [[Henry Cavendish]] had discovered that air contains a small proportion of a substance less reactive than [[nitrogen]].<ref name="Ozima 1">{{harvnb|Ozima|2002|p=1}}</ref> A century later, in 1895, [[John Strutt, 3rd Baron Rayleigh|Lord Rayleigh]] discovered that samples of nitrogen from the air were of a different [[density]] than nitrogen resulting from [[chemical reaction]]s. Along with Scottish scientist [[William Ramsay]] at [[University College, London]], Lord Rayleigh theorized that the nitrogen extracted from air was mixed with another gas, leading to an experiment that successfully isolated a new element, argon, from the Greek word {{lang|grc|ἀργός}} ({{lang|grc-Latn|argós}}, "idle" or "lazy").<ref name="Ozima 1" /> With this discovery, they realized an entire class of [[gas]]es was missing from the periodic table. During his search for argon, Ramsay also managed to isolate helium for the first time while heating [[cleveite]], a mineral. In 1902, having accepted the evidence for the elements helium and argon, [[Dmitri Mendeleev]] included these noble gases as group&nbsp;0 in his arrangement of the elements, which would later become the periodic table.<ref>{{harvnb|Mendeleev|1903|p=497}}</ref>

Ramsay continued his search for these gases using the method of [[fractional distillation]] to separate [[liquid air]] into several components. In 1898, he discovered the elements [[krypton]], [[neon]], and [[xenon]], and named them after the Greek words {{lang|grc|κρυπτός}} ({{lang|grc-Latn|kryptós}}, "hidden"), {{lang|grc|νέος}} ({{lang|grc-Latn|néos}}, "new"), and {{lang|grc|ξένος}} ({{lang|grc-Latn|ksénos}}, "stranger"), respectively. [[Radon]] was first identified in 1898 by [[Friedrich Ernst Dorn]],<ref>{{cite journal|title=Discovery of Radon|last=Partington|first=J. R.|journal=[[Nature (journal)|Nature]]|volume=179|issue=4566|page=912|year=1957|doi=10.1038/179912a0|bibcode=1957Natur.179..912P|s2cid=4251991|doi-access=free}}</ref> and was named ''radium emanation'', but was not considered a noble gas until 1904 when its characteristics were found to be similar to those of other noble gases.<ref name="brit">{{cite encyclopedia|encyclopedia=[[Encyclopædia Britannica]]|year=2008|title=Noble Gas|url=https://www.britannica.com/eb/article-9110613/noble-gas}}</ref> Rayleigh and Ramsay received the 1904 [[Nobel Prize]]s in Physics and in Chemistry, respectively, for their discovery of the noble gases;<ref>{{cite web |title=The Nobel Prize in Physics 1904 Presentation Speech |author=Cederblom, J. E. |year=1904 |url=http://nobelprize.org/nobel_prizes/physics/laureates/1904/press.html}}</ref><ref name=nobelchem>{{cite web |title=The Nobel Prize in Chemistry 1904 Presentation Speech |author=Cederblom, J. E. |year=1904 |url=http://nobelprize.org/nobel_prizes/chemistry/laureates/1904/press.html}}</ref> in the words of J. E. Cederblom, then president of the [[Royal Swedish Academy of Sciences]], "the discovery of an entirely new group of elements, of which no single representative had been known with any certainty, is something utterly unique in the history of chemistry, being intrinsically an advance in science of peculiar significance".<ref name=nobelchem/>

The discovery of the noble gases aided in the development of a general understanding of [[Atomic theory|atomic structure]]. In 1895, French chemist [[Henri Moissan]] attempted to form a reaction between [[fluorine]], the most [[electronegativity|electronegative]] element, and argon, one of the noble gases, but failed. Scientists were unable to prepare compounds of argon until the end of the 20th century, but these attempts helped to develop new theories of atomic structure. Learning from these experiments, Danish physicist [[Niels Bohr]] proposed in 1913 that the [[electron]]s in atoms are arranged in [[electron shell|shells]] surrounding the [[atomic nucleus|nucleus]], and that for all noble gases except helium the outermost shell always contains eight electrons.<ref name="brit" /> In 1916, [[Gilbert N. Lewis]] formulated the ''[[octet rule]]'', which concluded an octet of electrons in the outer shell was the most stable arrangement for any atom; this arrangement caused them to be unreactive with other elements since they did not require any more electrons to complete their outer shell.<ref>{{cite journal |author1=Gillespie, R. J. |author2=Robinson, E. A. |title=Gilbert N. Lewis and the chemical bond: the electron pair and the octet rule from 1916 to the present day |journal=J Comput Chem |volume=28 |issue=1 |pages=87–97 |year=2007 |pmid=17109437 |doi=10.1002/jcc.20545|doi-access=free }}</ref>

In 1962, [[Neil Bartlett (chemist)|Neil Bartlett]] discovered the first chemical compound of a noble gas, [[xenon hexafluoroplatinate]].<ref name="bartlett">{{cite journal|title=Xenon hexafluoroplatinate Xe<sup>+</sup>[PtF<sub>6</sub>]<sup>−</sup>|last=Bartlett|first=N.|journal=[[Proceedings of the Chemical Society]]|issue=6|page=218|year=1962|doi=10.1039/PS9620000197}}</ref> Compounds of other noble gases were discovered soon after: in 1962 for radon, [[radon difluoride]] ({{chem|Rn||F|2}}),<ref>{{cite journal|author1=Fields, Paul R. |author2=Stein, Lawrence |author3=Zirin, Moshe H. |title=Radon Fluoride|journal=[[Journal of the American Chemical Society]]|year=1962|volume=84|issue=21|pages=4164–4165|doi=10.1021/ja00880a048|bibcode=1962JAChS..84.4164F }}</ref> which was identified by radiotracer techniques and in 1963 for krypton, [[krypton difluoride]] ({{chem|Kr||F|2}}).<ref>{{cite journal|author1=Grosse, A. V. |author2=Kirschenbaum, A. D. |author3=Streng, A. G. |author4=Streng, L. V. |title=Krypton Tetrafluoride: Preparation and Some Properties|journal=Science|year=1963|volume=139|pages=1047–1048|doi=10.1126/science.139.3559.1047|pmid=17812982|issue=3559|bibcode=1963Sci...139.1047G}}</ref> The first stable compound of argon was reported in 2000 when [[argon fluorohydride]] (HArF) was formed at a temperature of {{convert|40|K}}.<ref>{{cite journal|title=A stable argon compound|journal=[[Nature (journal)|Nature]]|issue= 6798|pages=874–876|year=2000|doi=10.1038/35022551|author1=Khriachtchev, Leonid |author2=Pettersson, Mika |author3=Runeberg, Nino |author4=Lundell, Jan |author5=Räsänen, Markku |volume=406|pmid=10972285 |bibcode=2000Natur.406..874K|s2cid=4382128}}</ref>

In October 2006, scientists from the Joint Institute for Nuclear Research and [[Lawrence Livermore National Laboratory]] successfully created synthetically [[oganesson]], the seventh element in group&nbsp;18,<ref>{{cite journal|journal=Pure Appl. Chem.|volume=83|issue=7|year=2011|title=Discovery of the elements with atomic numbers greater than or equal to 113 (IUPAC Technical Report)*|author1=Barber, Robert C. |author2=Karol, Paul J. |author3=Nakahara, Hiromichi |author4=Vardaci, Emanuele |author5=Vogt, Erich W. |name-list-style=amp |url=http://iupac.org/publications/pac/pdf/2011/pdf/8307x1485.pdf|access-date=30 May 2014|publisher=IUPAC|doi=10.1515/ci.2011.33.5.25b }}</ref> by bombarding [[californium]] with calcium.<ref>{{cite journal |last1=Oganessian |first1=Yu. Ts. |title=Synthesis of the isotopes of elements 118 and 116 in the {{SimpleNuclide |Californium |249}} and {{SimpleNuclide |Curium |245}} + {{SimpleNuclide |Calcium |48}} fusion reactions |journal=Physical Review C |volume=74 |issue=4 |article-number=44602 |year=2006 |doi=10.1103/PhysRevC.74.044602 |last2=Utyonkov |first2=V. |last3=Lobanov |first3=Yu. |last4=Abdullin |first4=F. |last5=Polyakov |first5=A. |bibcode=2006PhRvC..74d4602O |display-authors=5 |last6=Shirokovsky |first6=I. |last7=Tsyganov |first7=Yu. |last8=Voinov |first8=A. |last9=Gulbekian |first9=G. |last10=Bogomolov |first10=S. |last11=Gikal |first11=B. |last12=Mezentsev |first12=A. |last13=Iliev |first13=S. |last14=Subbotin |first14=V. |last15=Sukhov |first15=A. |last16=Subotic |first16=K. |last17=Zagrebaev |first17=V. |last18=Vostokin |first18=G. |last19=Itkis |first19=M. |last20=Moody |first20=K. |last21=Patin |first21=J. |last22=Shaughnessy |first22=D. |last23=Stoyer |first23=M. |last24=Stoyer |first24=N. |last25=Wilk |first25=P. |last26=Kenneally |first26=J. |last27=Landrum |first27=J. |last28=Wild |first28=J. |last29=Lougheed |first29=R.|doi-access=free }}
</ref>
{{clear right}}

==Physical and atomic properties==
{| class="wikitable" style="text-align: center;"
! [[Chemical property|Property]]<ref name=brit /><ref name=greenwood891/>|| [[Helium]] || [[Neon]] || [[Argon]] || [[Krypton]] || [[Xenon]] || [[Radon]] ||[[Oganesson]]
|-
|align="left"|[[Density]] (g/[[litre|dm<sup>3</sup>]]) || 0.1786 || 0.9002 || 1.7818 || 3.708 || 5.851 || 9.97|| 7200 (predicted)<ref name=og>{{cite journal| journal=[[Angew. Chem. Int. Ed.]]| volume=59| issue=52| pages=23636–23640| date=2020| title=Oganesson: A Noble Gas Element That Is Neither Noble Nor a Gas| first1=Odile |last1=Smits |first2=Jan-Michael |last2=Mewes |first3=Paul |last3=Jerabek |first4=Peter |last4=Schwerdtfeger| doi=10.1002/anie.202011976| pmid=32959952| pmc=7814676| doi-access=free}}</ref>
|-
|align="left"|[[Boiling point]] (K) || 4.4 || 27.3 || 87.4 || 121.5 || 166.6 || 211.5|| 450±10 (predicted)<ref name=og/>
|-
|align="left"|[[Melting point]] (K) || –<ref>
[[Liquid helium]] will only solidify if exposed to pressures well above atmospheric pressure, an effect explainable with quantum mechanics</ref> || 24.7 || 83.6 || 115.8 || 161.7 || 202.2|| 325±15 (predicted)<ref name=og/>
|-
|align="left"|[[Enthalpy of vaporization]] (kJ/mol) || 0.08 || 1.74 || 6.52 || 9.05 || 12.65 || 18.1|| – 
|-
|align="left"|[[Solubility]] in water at 20&nbsp;°C (cm<sup>3</sup>/kg) || 8.61 || 10.5 || 33.6 || 59.4 || 108.1 || 230|| – 
|-
|align="left"| [[Atomic number]] || 2 || 10 || 18 || 36 || 54 || 86||118
|-
|align="left"|[[Atomic radius]] (calculated) ([[picometer|pm]]) || 31 || 38 || 71 || 88 || 108 || 120|| – 
|-
|align="left"|[[Ionization energy]] (kJ/mol) || 2372 || 2080 || 1520 || 1351 || 1170 || 1037|| 839 (predicted)<ref>{{cite web|title = Organesson: Properties of Free Atoms|url = https://www.webelements.com/oganesson/atoms.html|website = WebElements: THE periodic table on the WWW|year = 2020|access-date = 30 December 2020|first = Mark|last = Winter}}</ref>
|-
|-
|align="left"|[[Allen electronegativity|Electronegativity]]<ref>{{cite journal|doi=10.1021/ja00207a003|title=Electronegativity is the average one-electron energy of the valence-shell electrons in ground-state free atoms|year=1989|author1=Allen, Leland C.|journal=[[Journal of the American Chemical Society]]|volume=111|pages=9003–9014|issue=25|bibcode=1989JAChS.111.9003A }}</ref> || 4.16|| 4.79|| 3.24|| 2.97|| 2.58|| 2.60|| 2.59<ref>{{cite journal|doi=10.1038/s41467-021-22429-0|title=Thermochemical Electronegativities of the Elements|year=2021|author1=Tantardini, Christian|author2=Oganov, Artem R.|journal=[[Nature Communications]]|volume=12|pages=2087–2095|issue=1|pmid=33828104 |pmc=8027013 |bibcode=2021NatCo..12.2087T }}</ref>
|}
{{Hatnote|For more data, see [[Noble gas (data page)]].}}

The noble gases have weak [[interatomic force]], and consequently have very low [[Melting point|melting]] and [[boiling point]]s. They are all [[monatomic]] [[gas]]es under [[Standard temperature and pressure|standard conditions]], including the [[Chemical element|elements]] with larger [[atomic mass]]es than many normally [[solid]] elements.<ref name="brit"/> [[Helium]] has several unique qualities when compared with other elements: its boiling point at 1&nbsp;atm is lower than those of any other known [[Chemical substance|substance]]; it is the only element known to exhibit [[superfluidity]]; and, it is the only element that cannot be solidified by cooling at [[atmospheric pressure]]<ref name = Wilks /> (an effect explained by [[quantum mechanics]] as its [[zero point energy]] is too high to permit [[freezing]])<ref>{{cite web|year = 2008|url = http://www.phys.ualberta.ca/~therman/lowtemp/projects1.htm|title = John Beamish's Research on Solid Helium|archive-url = https://web.archive.org/web/20080531145546/http://www.phys.ualberta.ca/~therman/lowtemp/projects1.htm|archive-date = 31 May 2008|publisher = Department of Physics, [[University of Alberta]]}}</ref> – a [[pressure]] of {{convert|25|atm|kPa psi|lk=on}} must be applied at a [[temperature]] of {{convert|0.95|K}} to convert it to a solid<ref name = Wilks>{{cite book|title = The Properties of Liquid and Solid Helium|chapter-url = https://archive.org/details/propertiesofliqu0000wilk|chapter-url-access = registration|first = John|last = Wilks|year = 1967|place = Oxford|publisher = [[Clarendon Press]]|isbn = 978-0-19-851245-5|chapter = Introduction}}</ref> while a pressure of about {{cvt|113500|atm|kPa psi}} <!--115 ± 2 kbar in ref, converted to atm for consistency--> is required at [[room temperature]].<ref>{{cite journal|last1 = Pinceaux|first1 = J.-P.|last2 = Maury|first2 = J.-P.|last3 = Besson|first3 = J.-M.|title = Solidification of helium, at room temperature under high pressure|journal = [[Journal de Physique Lettres]]|year = 1979|volume = 40|issue = 13|pages = 307–308|doi = 10.1051/jphyslet:019790040013030700| s2cid=40164915 |url = https://hal.archives-ouvertes.fr/jpa-00231630/file/ajp-jphyslet_1979_40_13_307_0.pdf}}</ref> The noble gases up to xenon have multiple stable [[isotope]]s; krypton and xenon also have naturally occurring [[radioisotope]]s, namely <sup>78</sup>Kr, <sup>124</sup>Xe, and <sup>136</sup>Xe<!-- There are pages covering the isotopes of these elements but none yet for these specific isotopes. -->, all have very long lives (> 10<sup>21</sup> years) and can undergo [[double electron capture]] or [[double beta decay]]. Radon has no [[stable isotope]]s; its longest-lived isotope, [[radon-222|<sup>222</sup>Rn]], has a [[half-life]] of 3.8&nbsp;days and decays to form helium and [[polonium]], which ultimately decays to [[lead]].<ref name="brit" /> Oganesson also has no stable isotopes, and its only known isotope <sup>294</sup>Og <!-- There is a page in Wikipedia covering isotopes of Oganesson, but none have yet been created on the topic of this specific isotope. -->is very short-lived (half-life 0.7&nbsp;ms). Melting and boiling points increase going down the group.

<!-- This image is placed here because: straddling with the other images; it is next to the first paragraph that discusses ionization potential; it does not get bumped down by the Physical Properties table. I've tried to put the image lower because the text gets squeezed too much on a resolution of 1200x800-->[[File:First Ionization Energy blocks.svg|left|thumb|upright=3|This is a plot of [[ionization potential]] versus [[atomic number]]. The noble gases have the largest ionization potential for each period, although period 7 is expected to break this trend because the predicted [[Molar ionization energies of the elements|first ionization energy]] of oganesson (Z = 118) is lower than those of elements 110–112.|alt=A graph of ionization energy vs. atomic number showing sharp peaks for the noble gas atoms.]]

The noble gas [[atom]]s, like atoms in most groups, increase steadily in [[atomic radius]] from one [[period (periodic table)|period]] to the next due to the increasing number of [[electron]]s. The [[Atomic radius|size of the atom]] is related to several properties. For example, the [[ionization potential]] decreases with an increasing radius because the [[valence electron]]s in the larger noble gases are farther away from the [[atomic nucleus|nucleus]] and are therefore not held as tightly together by the atom. Noble gases have the largest ionization potential among the elements of each period, which reflects the stability of their electron configuration and is related to their relative lack of [[Reactivity (chemistry)|chemical reactivity]].<ref name=greenwood891/> Some of the heavier noble gases, however, have ionization potentials small enough to be comparable to those of other elements and [[molecule]]s. It was the insight that xenon has an ionization potential similar to that of the [[oxygen]] molecule that led [[Neil Bartlett (chemist)|Bartlett]] to attempt oxidizing xenon using [[platinum hexafluoride]], an [[oxidizing agent]] known to be strong enough to react with oxygen.<ref name=bartlett/> Noble gases cannot accept an electron to form stable [[anion]]s; that is, they have a negative [[electron affinity]].<ref>{{cite journal |journal=[[Journal of Chemical Education]]|last=Wheeler |first=John C. |year=1997 |volume=74 |issue=1 |pages=123–127 |title=Electron Affinities of the Alkaline Earth Metals and the Sign Convention for Electron Affinity|bibcode= 1997JChEd..74..123W |doi= 10.1021/ed074p123 }}; {{cite journal|journal=[[Chemical Reviews]] |year=1994 |volume=94 |pages=2291–2318|author1=Kalcher, Josef |author2=Sax, Alexander F. |title=Gas Phase Stabilities of Small Anions: Theory and Experiment in Cooperation |doi=10.1021/cr00032a004|issue=8}}</ref>

The [[macroscopic]] [[physical properties]] of the noble gases are dominated by the weak [[van der Waals forces]] between the atoms. The attractive [[force]] increases with the size of the atom as a result of the increase in [[polarizability]] and the decrease in ionization potential. This results in systematic group trends: as one goes down group&nbsp;18, the atomic radius increases, and with it the [[Intermolecular force|interatomic forces]] increase, resulting in an increasing melting point, boiling point, [[enthalpy of vaporization]], and [[solubility]]. The increase in [[density]] is due to the increase in [[atomic mass]].<ref name=greenwood891>{{harvnb|Greenwood|1997|p=891}}</ref>

The noble gases are nearly [[ideal gas]]es under standard conditions, but their deviations from the [[ideal gas law]] provided important clues for the study of [[intermolecular interactions]]. The [[Lennard-Jones potential]], often used to model [[Intermolecular force|intermolecular interactions]], was deduced in 1924 by [[John Lennard-Jones]] from [[experimental data]] on argon before the development of [[quantum mechanics]] provided the tools for understanding intermolecular forces from [[first principles]].<ref>{{cite journal|title=John Edward Lennard-Jones. 1894–1954 |last=Mott|first=N. F.|journal=[[Biographical Memoirs of Fellows of the Royal Society]]|pages=175–184|volume=1|year=1955|doi=10.1098/rsbm.1955.0013|doi-access=free}}</ref> The theoretical analysis of these interactions became tractable because the noble gases are monatomic and the atoms spherical, which means that the interaction between the atoms is independent of direction, or [[isotropic]].

==Chemical properties==
[[File:Electron shell 010 Neon - no label.svg|thumb|Neon, like all noble gases, has a full [[valence shell]]. Noble gases have eight electrons in their outermost shell, except in the case of helium, which has two.|alt=An atomic shell diagram with neon core, 2 electrons in the inner shell and 8 in the outer shell.]]

The noble gases are colorless, odorless, tasteless, and nonflammable under [[Standard temperature and pressure|standard conditions]].<ref>{{cite book |title=Ullmann's Encyclopedia of Industrial Chemistry – Volume 23 |year=2003 |publisher=John Wiley & Sons |author=Wiley-VCH |page=217 }}</ref> They were once labeled ''[[Group (periodic table)|group]]&nbsp;0'' in the [[periodic table]] because it was believed they had a [[valence (chemistry)|valence]] of zero, meaning their [[atom]]s cannot combine with those of other [[Chemical element|elements]] to form [[chemical compound|compounds]]. However, it was later discovered some do indeed form compounds, causing this label to fall into disuse.<ref name="brit" />

===Electron configuration===
{{Further|Noble gas configuration}}
Like other groups, the members of this [[Group (periodic table)|family]] show patterns in its [[electron configuration]], especially the outermost shells resulting in trends in chemical behavior:

{| class="wikitable" style="white-space:nowrap;"
|-
!''[[Atomic number|Z]]'' !! [[Chemical element|Element]] !! Electrons per [[Electron shell|shell]]
|-
| 2 || [[helium]] || 2
|-
| 10 || [[neon]] || 2, 8
|-
| 18 || [[argon]] || 2, 8, 8
|-
| 36 || [[krypton]] || 2, 8, 18, 8
|-
| 54 || [[xenon]] || 2, 8, 18, 18, 8
|-
| 86 || [[radon]] || 2, 8, 18, 32, 18, 8
|-
| 118 || [[oganesson]] || 2, 8, 18, 32, 32, 18, 8<br/>(predicted)
|}

The noble gases have full valence [[electron shells]]. [[Valence electron]]s are the outermost [[electron]]s of an atom and are normally the only electrons that participate in [[chemical bond]]ing. Atoms with full valence electron shells are extremely [[Stable nuclide|stable]] and therefore do not tend to form [[chemical bond]]s and have little tendency to [[Ion|gain or lose electrons]].<ref>{{harvnb|Ozima|2002|p=35}}</ref> However, heavier noble gases such as radon are held less firmly together by [[electromagnetic force]] than lighter noble gases such as helium, making it easier to remove outer electrons from heavy noble gases.

As a result of a full shell, the noble gases can be used in conjunction with the [[electron configuration]] notation to form the ''noble gas notation''. To do this, the nearest noble gas that precedes the element in question is written first, and then the electron configuration is continued from that point forward. For example, the electron notation of
[[phosphorus]] is {{nowrap|1s<sup>2</sup> 2s<sup>2</sup> 2p<sup>6</sup> 3s<sup>2</sup> 3p<sup>3</sup>}}, while the noble gas notation is {{nowrap|[Ne] 3s<sup>2</sup> 3p<sup>3</sup>}}. This more compact notation makes it easier to identify elements, and is shorter than writing out the full notation of [[atomic orbital]]s.<ref>{{harvnb|CliffsNotes|2007|p=15}}</ref>

The noble gases cross the boundary between [[block (periodic table)|blocks]]—helium is an [[Block (periodic table)#s-block|s-element]] whereas the rest of members are [[Block (periodic table)#p-block|p-elements]]—which is unusual among the [[International Union of Pure and Applied Chemistry|IUPAC]] groups. All other IUPAC groups contain elements from ''one'' block each. This causes some inconsistencies in trends across the table, and on those grounds some [[chemist]]s have proposed that helium should be moved to [[alkaline earth metal|group 2]] to be with other s<sup>2</sup> elements,<ref>{{cite journal |last1=Grochala |first1=Wojciech |date=1 November 2017 |title=On the position of helium and neon in the Periodic Table of Elements |journal=Foundations of Chemistry |volume=20 |pages=191–207 |issue=2018 |doi=10.1007/s10698-017-9302-7 |doi-access=free }}</ref><ref>{{cite journal |last1=Bent Weberg |first1=Libby |date=18 January 2019 |title="The" periodic table |url=https://cen.acs.org/articles/97/i3/Reactions.html |journal=Chemical & Engineering News |volume=97 |issue=3 |access-date=27 March 2020 |archive-date=1 February 2020 |archive-url=https://web.archive.org/web/20200201200009/https://cen.acs.org/articles/97/i3/Reactions.html |url-status=live }}</ref><ref>{{cite journal |last1=Grandinetti |first1=Felice |date=23 April 2013 |title=Neon behind the signs |journal=Nature Chemistry |volume=5 |issue=2013 |page=438 |doi=10.1038/nchem.1631 |pmid=23609097 |bibcode=2013NatCh...5..438G |doi-access=free }}</ref> but this change has not generally been adopted.

===Compounds===
{{Main|Noble gas compound}}
[[File:Xenon-tetrafluoride-3D-vdW.png|thumb|left|Structure of [[xenon tetrafluoride]] ({{chem|Xe||F|4}}), one of the first noble gas compounds to be discovered|alt=A model of planar chemical molecule with a blue center atom (Xe) symmetrically bonded to four peripheral atoms (fluorine).]]

The noble gases show extremely low [[reactivity (chemistry)|chemical reactivity]]; consequently, only a few hundred [[noble gas compound]]s have been formed. Neutral [[chemical compound|compounds]] in which helium and neon are involved in [[chemical bond]]s have not been formed (although some helium-containing [[ion]]s exist and there is some theoretical evidence for a few neutral helium-containing ones), while xenon, krypton, and argon have shown only minor reactivity.<ref name=Ngcomp>{{cite journal|last=Grochala|first=Wojciech|title=Atypical compounds of gases, which have been called noble|journal=[[Chemical Society Reviews]]|year=2007|issue=10|pages=1632–1655|doi=10.1039/b702109g|volume=36|pmid=17721587|url=http://www.chem.uw.edu.pl/people/WGrochala/Ng_essay.pdf?origin%3Dpublication_detail|access-date=25 October 2017|archive-date=26 October 2017|archive-url=https://web.archive.org/web/20171026111020/http://beta.chem.uw.edu.pl/people/WGrochala/Ng_essay.pdf?origin%3Dpublication_detail}}</ref>

In 1933, [[Linus Pauling]] predicted that the heavier noble gases could form compounds with fluorine and oxygen. He predicted the existence of [[krypton hexafluoride]] ({{chem|KrF|6}}) and [[xenon hexafluoride]] ({{chem|XeF|6}}) and speculated that [[xenon octafluoride]] ({{chem|XeF|8}}) might exist as an unstable compound, and suggested that [[xenic acid]] could form [[perxenate]] salts.<ref>{{cite journal|title=The Formulas of Antimonic Acid and the Antimonates|last=Pauling|first=Linus|journal=[[Journal of the American Chemical Society]]|volume=55|issue=5|pages=1895–1900|year=1933| doi=10.1021/ja01332a016|bibcode=1933JAChS..55.1895P }}</ref><ref name="Holloway">{{harvnb|Holloway|1968}}</ref> These predictions were shown to be generally accurate, except that {{chem|XeF|8}} is now thought to be both [[thermodynamic stability|thermodynamically]] and [[kinetic theory of gases|kinetically]] unstable.<ref>{{cite journal|last=Seppelt|first=Konrad|year=1979|title=Recent developments in the Chemistry of Some Electronegative Elements|journal=[[Accounts of Chemical Research]]|volume=12|pages=211–216|doi=10.1021/ar50138a004|issue=6}}</ref>

[[Xenon compounds]] are the most numerous of the noble gas compounds that have been formed.<ref>{{cite journal|last=Moody|first=G. J.|title=A Decade of Xenon Chemistry|journal=Journal of Chemical Education|year=1974|issue=10|volume=51|pages=628–630| url=http://www.eric.ed.gov/ERICWebPortal/custom/portlets/recordDetails/detailmini.jsp?_nfpb=true&_&ERICExtSearch_SearchValue_0=EJ111480&ERICExtSearch_SearchType_0=no&accno=EJ111480|access-date=16 October 2007|doi=10.1021/ed051p628|bibcode= 1974JChEd..51..628M }}</ref> Most of them have the xenon atom in the [[oxidation state]] of +2, +4, +6, or +8 bonded to highly [[electronegative]] atoms such as fluorine or oxygen, as in [[xenon difluoride]] ({{chem|XeF|2}}), [[xenon tetrafluoride]] ({{chem|XeF|4}}), [[xenon hexafluoride]] ({{chem|XeF|6}}), [[xenon tetroxide]] ({{chem|XeO|4}}), and [[sodium perxenate]] ({{chem|Na|4|XeO|6}}). Xenon reacts with fluorine to form numerous xenon fluorides according to the following equations:

::Xe + F<sub>2</sub> → XeF<sub>2</sub>
::Xe + 2F<sub>2</sub> → XeF<sub>4</sub>
::Xe + 3F<sub>2</sub> → XeF<sub>6</sub>

Some of these compounds have found use in [[chemical synthesis]] as [[oxidizing agent]]s; {{chem|XeF|2}}, in particular, is commercially available and can be used as a [[fluorination|fluorinating]] agent.<ref>{{cite journal |title=Fluorination with XeF<sub>2</sub>. 44. Effect of Geometry and Heteroatom on the Regioselectivity of Fluorine Introduction into an Aromatic Ring |author1=Zupan, Marko |author2=Iskra, Jernej |author3=Stavber, Stojan |journal=J. Org. Chem. |year=1998 |volume=63 |issue=3 |pages=878–880 |doi=10.1021/jo971496e |pmid=11672087}}</ref> As of 2007, about five hundred compounds of xenon bonded to other elements have been identified, including organoxenon compounds (containing xenon bonded to carbon), and xenon bonded to nitrogen, chlorine, gold, mercury, and xenon itself.<ref name=Ngcomp/><ref>{{harvnb|Harding|2002|pp=90–99}}</ref> Compounds of xenon bound to boron, hydrogen, bromine, iodine, beryllium, sulfur, titanium, copper, and silver have also been observed but only at low temperatures in noble gas [[matrix isolation|matrices]], or in supersonic noble gas jets.<ref name=Ngcomp/>

[[Radon]] is more reactive than xenon, and forms chemical bonds more easily than xenon does. However, due to the high radioactivity and short half-life of [[isotopes of radon|radon isotopes]], only a few [[fluoride]]s and [[oxide]]s of radon have been formed in practice.<ref>.{{cite journal|title=The Chemistry of Radon|volume=51|journal=Russian Chemical Reviews|year=1982|issue=1|pages=12–20|author1=Avrorin, V. V. |author2=Krasikova, R. N. |author3=Nefedov, V. D. |author4=Toropova, M. A. |doi=10.1070/RC1982v051n01ABEH002787|bibcode= 1982RuCRv..51...12A |s2cid=250906059 }}</ref> Radon goes further towards metallic behavior than xenon; the difluoride RnF<sub>2</sub> is highly ionic, and cationic Rn<sup>2+</sup> is formed in halogen fluoride solutions. For this reason, kinetic hindrance makes it difficult to oxidize radon beyond the +2 state. Only tracer experiments appear to have succeeded in doing so, probably forming RnF<sub>4</sub>, RnF<sub>6</sub>, and RnO<sub>3</sub>.<ref name=Stein>{{cite journal |last1=Stein |first1=Lawrence |date=1983 |title=The Chemistry of Radon |journal=Radiochimica Acta |volume=32 |issue=1–3 |pages=163–171 |doi=10.1524/ract.1983.32.13.163|s2cid=100225806 }}</ref><ref>{{cite journal |last1=Liebman |first1=Joel F. |date=1975 |title=Conceptual Problems in Noble Gas and Fluorine Chemistry, II: The Nonexistence of Radon Tetrafluoride |journal=Inorg. Nucl. Chem. Lett. |volume=11 |issue=10 |pages=683–685 |doi=10.1016/0020-1650(75)80185-1}}</ref><ref>{{cite journal |last1=Seppelt |first1=Konrad |date=2015 |title=Molecular Hexafluorides |journal=Chemical Reviews |volume=115 |issue=2 |pages=1296–1306 |doi=10.1021/cr5001783|pmid=25418862 }}</ref>

Krypton is less reactive than xenon, but several compounds have been reported with krypton in the [[oxidation state]] of +2.<ref name=Ngcomp/> [[Krypton difluoride]] is the most notable and easily characterized. Under extreme conditions, krypton reacts with fluorine to form KrF<sub>2</sub> according to the following equation:

::Kr + F<sub>2</sub> → KrF<sub>2</sub>

Compounds in which krypton forms a single bond to nitrogen and oxygen have also been characterized,<ref>{{cite journal|doi=10.1016/S0010-8545(02)00202-3|title=The chemistry of krypton|year=2002|author=Lehmann, J|journal=Coordination Chemistry Reviews|volume=233–234|pages=1–39}}</ref> but are only stable below {{convert|-60|C}} and {{convert|-90|C}} respectively.<ref name=Ngcomp/>

Krypton atoms chemically bound to other nonmetals (hydrogen, chlorine, carbon) as well as some late [[transition metal]]s (copper, silver, gold) have also been observed, but only either at low temperatures in noble gas matrices, or in supersonic noble gas jets.<ref name=Ngcomp/> Similar conditions were used to obtain the first few compounds of argon in 2000, such as [[argon fluorohydride]] (HArF), and some bound to the late transition metals copper, silver, and gold.<ref name=Ngcomp/> As of 2007, no stable neutral molecules involving covalently bound helium or neon are known.<ref name=Ngcomp/>

Extrapolation from periodic trends predict that oganesson should be the most reactive of the noble gases; more sophisticated theoretical treatments indicate greater reactivity than such extrapolations suggest, to the point where the applicability of the descriptor "noble gas" has been questioned.<ref>{{cite journal |last=Roth |first=Klaus |year=2017 |title=Ist das Element 118 ein Edelgas? |trans-title=Is Element 118 a Noble Gas? |journal=[[Chemie in unserer Zeit]] |language=German |volume=51 |issue=6 |pages=418–426 |doi=10.1002/ciuz.201700838}}<br />Translated into English by W. E. Russey and published in three parts in [[ChemViews Magazine]]:<br />{{cite magazine |last=Roth |first=Klaus |date=3 April 2018 |title=New Kids on the Table: Is Element 118 a Noble Gas? – Part 1 |url=https://www.chemistryviews.org/details/ezine/10907570/New_Kids_on_the_Table_Is_Element_118_a_Noble_Gas__Part_1.html |magazine=[[ChemViews Magazine]] |doi=10.1002/chemv.201800029}}<br />{{cite magazine |last=Roth |first=Klaus |date=1 May 2018 |title=New Kids on the Table: Is Element 118 a Noble Gas? – Part 2 |url=https://www.chemistryviews.org/details/ezine/11002036/New_Kids_on_the_Table_Is_Element_118_a_Noble_Gas__Part_2.html |magazine=[[ChemViews Magazine]] |doi=10.1002/chemv.201800033}}<br />{{cite magazine |last=Roth |first=Klaus |date=5 June 2018 |title=New Kids on the Table: Is Element 118 a Noble Gas? – Part 3 |url=https://www.chemistryviews.org/details/ezine/11046703/New_Kids_on_the_Table_Is_Element_118_a_Noble_Gas__Part_3.html |magazine=[[ChemViews Magazine]] |doi=10.1002/chemv.201800046}}</ref> Oganesson is expected to be rather like [[silicon]] or [[tin]] in group 14:<ref name=primefan>{{cite web |url=http://www.primefan.ru/stuff/chem/ptable/ptable.pdf |title=Есть ли граница у таблицы Менделеева? |trans-title=Is there a boundary to the Mendeleev table? |last=Kulsha |first=A. V. |website=www.primefan.ru |access-date=8 September 2018 |language=ru}}</ref> a reactive element with a common +4 and a less common +2 state,<ref name="BFricke">{{Cite journal |last1=Fricke |first1=Burkhard |year=1975 |title=Superheavy elements: a prediction of their chemical and physical properties |journal=Recent Impact of Physics on Inorganic Chemistry |volume=21 |pages=[https://archive.org/details/recentimpactofph0000unse/page/89 89–144] |doi=10.1007/BFb0116498 |url=https://archive.org/details/recentimpactofph0000unse/page/89 |access-date=4 October 2013 |series=Structure and Bonding |isbn=978-3-540-07109-9}}</ref><ref>[http://www.primefan.ru/stuff/chem/front2019.png Russian periodic table poster] by A. V. Kulsha and T. A. Kolevich</ref> which at room temperature and pressure is not a gas but rather a solid semiconductor. Empirical / experimental testing will be required to validate these predictions.<ref name=og/><ref name=semiconductor>{{cite journal |last1=Mewes |first1=Jan-Michael |last2=Smits |first2=Odile Rosette |first3=Paul |last3=Jerabek |first4=Peter |last4=Schwerdtfeger |date=25 July 2019 |title=Oganesson is a Semiconductor: On the Relativistic Band-Gap Narrowing in the Heaviest Noble-Gas Solids |journal=Angewandte Chemie |volume=58 |issue=40 |pages=14260–14264 |doi=10.1002/anie.201908327 |pmid=31343819 |pmc=6790653 }}</ref> (On the other hand, [[flerovium]], despite being in group 14, is predicted to be unusually volatile, which suggests noble gas-like properties.)<ref>{{Cite journal |last=Kratz |first=J. V. |date=2012-08-01 |title=The impact of the properties of the heaviest elements on the chemical and physical sciences |journal=Radiochimica Acta |language=en |volume=100 |issue=8–9 |pages=569–578 |doi=10.1524/ract.2012.1963 |s2cid=97915854 |issn=2193-3405|doi-access=free }}</ref><ref>{{Cite web |title=Indication for a volatile element 114 |url=http://doc.rero.ch/record/290779/files/ract.2010.1705.pdf |website=doc.rero.ch}}</ref>

The noble gases—including helium—can form stable [[molecular ion]]s in the gas phase. The simplest is the [[Helium hydride ion|helium hydride molecular ion]], HeH<sup>+</sup>, discovered in 1925.<ref>{{cite journal |author1=Hogness, T. R. |author2=Lunn, E. G. |title=The Ionization of Hydrogen by Electron Impact as Interpreted by Positive Ray Analysis |url=https://archive.org/details/sim_physical-review_1925-07_26_1/page/44 |journal=Physical Review |year=1925 |volume=26 |issue=1 |pages=44–55 |doi=10.1103/PhysRev.26.44 |bibcode=1925PhRv...26...44H}}</ref> Because it is composed of the two most abundant elements in the universe, hydrogen and helium, it was believed to occur naturally in the [[interstellar medium]], and it was finally detected in April 2019 using the airborne [[Stratospheric Observatory for Infrared Astronomy|SOFIA telescope]]. In addition to these ions, there are many known neutral [[excimer]]s of the noble gases. These are compounds such as ArF and KrF that are stable only when in an [[Excited state|excited electronic state]]; some of them find application in [[excimer laser]]s.

In addition to the compounds where a noble gas atom is involved in a [[covalent bond]], noble gases also form [[non-covalent]] compounds. The [[clathrate]]s, first described in 1949,<ref>{{cite journal |title=An Inert Gas Compound |author1=Powell, H. M. |author2=Guter, M. |name-list-style=amp |journal=Nature |volume=164 |pages=240–241 |year=1949 |doi=10.1038/164240b0 |pmid=18135950 |issue=4162|bibcode= 1949Natur.164..240P |s2cid=4134617 }}</ref> consist of a noble gas atom trapped within cavities of [[crystal lattice]]s of certain organic and inorganic substances. The essential condition for their formation is that the guest (noble gas) atoms must be of appropriate size to fit in the cavities of the host crystal lattice. For instance, argon, krypton, and xenon form clathrates with [[hydroquinone]], but helium and neon do not because they are too small or insufficiently [[Polarizability|polarizable]] to be retained.<ref>{{harvnb|Greenwood|1997|p=893}}</ref> Neon, argon, krypton, and xenon also form clathrate hydrates, where the noble gas is trapped in ice.<ref>{{cite journal |author=Dyadin, Yuri A.|doi=10.1070/MC1999v009n05ABEH001104 |title=Clathrate hydrates of hydrogen and neon |journal=Mendeleev Communications |volume=9 |issue=5 |year=1999 |pages=209–210|display-authors=etal}}</ref>

[[File:Endohedral fullerene.png|thumb|An endohedral fullerene compound containing a noble gas atom|alt=A skeletal structure of buckminsterfullerene with an extra atom in its center.]]

Noble gases can form [[Endohedral fullerenes#Non-metal doped fullerenes|endohedral fullerene]] compounds, in which the noble gas atom is trapped inside a [[fullerene]] molecule. In 1993, it was discovered that when {{chem|C|60}}, a spherical molecule consisting of 60&nbsp;[[carbon]]&nbsp;atoms, is exposed to noble gases at high pressure, [[Complex (chemistry)|complex]]es such as {{chem|He@C|60}} can be formed (the ''@'' notation indicates He is contained inside {{chem|C|60}} but not covalently bound to it).<ref>{{cite journal|title=Stable compounds of helium and neon. He@C60 and Ne@C60|author1=Saunders, M. |author2=Jiménez-Vázquez, H. A. |author3=Cross, R. J. |author4=Poreda, R. J. |journal=[[Science (journal)|Science]]|year=1993|volume=259|pages=1428–1430|doi=10.1126/science.259.5100.1428|pmid=17801275|issue=5100|bibcode= 1993Sci...259.1428S |s2cid=41794612 }}</ref> As of 2008, endohedral complexes with helium, neon, argon, krypton, and xenon have been created.<ref>{{cite journal|title=Incorporation of helium, neon, argon, krypton, and xenon into fullerenes using high pressure|author1=Saunders, Martin |author2=Jimenez-Vazquez, Hugo A. |author3=Cross, R. James |author4=Mroczkowski, Stanley |author5=Gross, Michael L. |author6=Giblin, Daryl E. |author7=Poreda, Robert J. |journal=[[J. Am. Chem. Soc.]]|year=1994|volume=116|issue=5|pages=2193–2194|doi=10.1021/ja00084a089|bibcode=1994JAChS.116.2193S }}</ref> These compounds have found use in the study of the structure and reactivity of fullerenes by means of the [[nuclear magnetic resonance]] of the noble gas atom.<ref>{{cite journal|last1=Frunzi|first1=Michael|last2=Cross|first2=R. Jame|last3=Saunders|first3=Martin|title=Effect of Xenon on Fullerene Reactions|journal=[[Journal of the American Chemical Society]]|year=2007|volume=129|doi=10.1021/ja075568n|pages=13343–13346|pmid=17924634|issue=43|bibcode=2007JAChS.12913343F |url=https://figshare.com/articles/journal_contribution/2977702}}</ref>

[[File:XeF2.svg|300px|thumb|left|Bonding in {{chem|XeF|2}} according to the 3-center-4-electron bond model|alt=Schematic illustration of bonding and antibonding orbitals (see text)]]
Noble gas compounds such as [[xenon difluoride]] ({{chem|XeF|2}}) are considered to be [[hypervalent]] because they violate the [[octet rule]]. Bonding in such compounds can be explained using a [[three-center four-electron bond]] model.<ref>{{harvnb|Greenwood|1997|p=897}}</ref><ref>{{harvnb|Weinhold|2005|pp=275–306}}</ref> This model, first proposed in 1951, considers bonding of three collinear atoms. For example, bonding in {{chem|XeF|2}} is described by a set of three [[molecular orbital]]s (MOs) derived from [[p-orbital]]s on each atom. Bonding results from the combination of a filled p-orbital from Xe with one half-filled p-orbital from each [[fluorine|F]] atom, resulting in a filled bonding orbital, a filled non-bonding orbital, and an empty [[antibonding]] orbital. The [[highest occupied molecular orbital]] is localized on the two terminal atoms. This represents a localization of charge that is facilitated by the high electronegativity of fluorine.<ref>{{cite journal|last=Pimentel|first=G. C.|title= The Bonding of Trihalide and Bifluoride Ions by the Molecular Orbital Method|url=https://archive.org/details/sim_journal-of-chemical-physics_1951-04_19_4/page/446|year=1951|issue=4|pages=446–448|doi=10.1063/1.1748245|journal=The Journal of Chemical Physics|volume=19|bibcode= 1951JChPh..19..446P }}</ref>

The chemistry of the heavier noble gases, krypton and xenon, are well established. The chemistry of the lighter ones, argon and helium, is still at an early stage, while a neon compound is yet to be identified.
{{clear}}

==Occurrence==
The abundances of the noble gases in the universe decrease as their [[atomic number]]s increase. Helium is the most common element in the [[universe]] after hydrogen, with a mass fraction of about 24%. Most of the helium in the universe was formed during [[Big Bang nucleosynthesis]], but the amount of helium is steadily increasing due to the fusion of hydrogen in [[stellar nucleosynthesis]] (and, to a very slight degree, the [[alpha decay]] of heavy elements).<ref>{{cite web|last=Weiss|first=Achim|title=Elements of the past: Big Bang Nucleosynthesis and observation|url=http://www.einstein-online.info/en/spotlights/BBN_obs/index.html|publisher=[[Max Planck Institute for Gravitational Physics]]|access-date=23 June 2008|archive-url=https://web.archive.org/web/20070208212728/http://www.einstein-online.info/en/spotlights/BBN_obs/index.html|archive-date=8 February 2007}}</ref><ref>{{cite journal|author=Coc, A.|title=Updated Big Bang Nucleosynthesis confronted to WMAP observations and to the Abundance of Light Elements|journal=[[Astrophysical Journal]]|volume=600|year=2004|pages=544–552|doi=10.1086/380121|bibcode=2004ApJ...600..544C|issue=2|arxiv= astro-ph/0309480 |s2cid=16276658|display-authors=etal}}</ref>

Abundances on Earth follow different trends; for example, helium is only the third most abundant noble gas in the atmosphere. The reason is that there is no [[primordial element|primordial]] helium in the atmosphere; due to the small mass of the atom, helium cannot be retained by the Earth's [[gravitational field]].<ref name=morrison>{{cite journal|first1=P.|last1=Morrison|last2=Pine|first2=J.|year=1955|title=Radiogenic Origin of the Helium Isotopes in Rock|journal=Annals of the New York Academy of Sciences|volume=62|issue=3|pages=71–92|doi=10.1111/j.1749-6632.1955.tb35366.x|bibcode= 1955NYASA..62...71M |s2cid=85015694}}</ref> Helium on Earth comes from the [[alpha decay]] of heavy elements such as [[uranium]] and [[thorium]] found in the Earth's [[Crust (geology)|crust]], and tends to accumulate in [[Natural gas field|natural gas deposit]]s.<ref name=morrison /> The abundance of argon, on the other hand, is increased as a result of the [[beta decay]] of [[potassium-40]], also found in the Earth's crust, to form [[argon-40]], which is the most abundant isotope of argon on Earth despite being relatively rare in the [[Solar System]]. This process is the basis for the [[potassium-argon dating]] method.<ref>{{cite web|url=http://www.geoberg.de/text/geology/07011601.php|title=<sup>40</sup>Ar/<sup>39</sup>Ar dating and errors|access-date=26 June 2008|publisher=[[Technische Universität Bergakademie Freiberg]]|date=16 January 2007|last=Scherer|first=Alexandra |archive-url= https://web.archive.org/web/20071014042248/http://geoberg.de/text/geology/07011601.php |archive-date=14 October 2007}}</ref>

Xenon has an unexpectedly low abundance in the atmosphere, in what has been called the ''missing xenon problem''; one theory is that the missing xenon may be trapped in minerals inside the Earth's crust.<ref>{{cite journal |first1=Chrystèle|last1=Sanloup |first2=Burkhard C. |last2=Schmidt |first3=Eva Maria Chamorro|last3=Perez |first4=Albert |last4=Jambon |first5=Eugene |last5=Gregoryanz |first6=Mohamed |last6=Mezouar |display-authors=2 |title=Retention of Xenon in Quartz and Earth's Missing Xenon|journal=Science|year=2005|volume=310|issue=5751|pages=1174–1177|doi= 10.1126/science.1119070|pmid=16293758|bibcode= 2005Sci...310.1174S |s2cid=31226092 }}</ref><ref>{{Cite journal |last=Zhu |first=Li |last2=Liu |first2=Hanyu |last3=Pickard |first3=Chris J. |last4=Zou |first4=Guangtian |last5=Ma |first5=Yanming |date=July 2014 |title=Reactions of xenon with iron and nickel are predicted in the Earth's inner core |url=https://www.nature.com/articles/nchem.1925 |journal=Nature Chemistry |language=en |volume=6 |issue=7 |pages=644–648 |doi=10.1038/nchem.1925 |issn=1755-4349|arxiv=1309.2169 }}</ref> Radon is formed in the [[lithosphere]] by the [[alpha decay]] of radium. It can seep into buildings through cracks in their foundation and accumulate in areas that are not well ventilated. Due to its high radioactivity, radon presents a significant health hazard; it is implicated in an estimated 21,000 [[lung cancer]] deaths per year in the United States alone.<ref>{{cite web| title= A Citizen's Guide to Radon| publisher= U.S. Environmental Protection Agency| date= 26 November 2007| url= http://www.epa.gov/radon/pubs/citguide.html| archive-url= https://web.archive.org/web/20030419085501/http://www.epa.gov/radon/pubs/citguide.html| archive-date= 19 April 2003| access-date= 26 June 2008}}</ref> Oganesson does not occur in nature and is instead created manually by scientists.
{| class="wikitable" style="text-align: center; margin-left: auto; margin-right: auto; border: none;"
! Abundance ||Helium||Neon||Argon||Krypton||Xenon||Radon
|-
|align="left"|Solar System (for each atom of silicon)<ref>{{cite journal| doi = 10.1086/375492| last = Lodders| first = Katharina|author-link=Katharina Lodders| date = 10 July 2003| title = Solar System Abundances and Condensation Temperatures of the Elements| journal = The Astrophysical Journal| publisher = The American Astronomical Society| volume = 591| issue = 2| pages = 1220–1247| url = http://weft.astro.washington.edu/courses/astro557/LODDERS.pdf| bibcode = 2003ApJ...591.1220L| s2cid = 42498829| access-date = 1 September 2015| archive-url = https://web.archive.org/web/20151107043527/http://weft.astro.washington.edu/courses/astro557/LODDERS.pdf| archive-date = 7 November 2015}}</ref>|| 2343 || 2.148 || 0.1025 || 5.515 × 10<sup>−5</sup> || 5.391 × 10<sup>−6</sup> || –
|-
|align="left"|Earth's atmosphere (volume fraction in [[parts per million|ppm]])<ref>{{cite web|access-date=1 June 2008|url=http://www.srh.noaa.gov/jetstream//atmos/atmos_intro.htm|title=The Atmosphere |publisher=[[National Weather Service]]}}</ref> || 5.20 || 18.20 || 9340.00 || 1.10 || 0.09 || (0.06–18) × 10<sup>−19</sup><ref name=ullmann/>
|-
|align="left"|Igneous rock (mass fraction in ppm)<ref name="greenwood891"/> || 3 × 10<sup>−3</sup> || 7 × 10<sup>−5</sup> || 4 × 10<sup>−2</sup> || – || – || 1.7 × 10<sup>−10</sup>
|}

<div style="float: right; padding-left: 10px;">
{| class="wikitable" style="text-align: center;"
! Gas || 2004 price ([[United States dollar|USD]]/m<sup>3</sup>)<ref name=kirk>{{cite book |title=Kirk Othmer Encyclopedia of Chemical Technology |author1=Hwang, Shuen-Chen |author2=Lein, Robert D. |author3=Morgan, Daniel A. |chapter=Noble Gases |doi=10.1002/0471238961.0701190508230114.a01 |pages=343–383 |year=2005 |publisher=Wiley}}</ref>
|-
|align=left| Helium (industrial grade) || 4.20–4.90
|-
|align=left| Helium (laboratory grade) || 22.30–44.90
|-
|align=left| Argon || 2.70–8.50
|-
|align=left| Neon || 60–120
|-
|align=left| Krypton || 400–500
|-
|align=left| Xenon || 4000–5000
|}
</div>
For large-scale use, helium is extracted by [[fractional distillation]] from natural gas, which can contain up to 7% helium.<ref>{{cite web| author = Winter, Mark| title = Helium: the essentials| publisher = University of Sheffield|year = 2008| url = http://www.webelements.com/helium/| access-date = 14 July 2008}}</ref>

== Extraction ==
Neon, argon, krypton, and xenon are obtained from air using the methods of [[liquefaction of gases]], to convert elements to a liquid state, and [[fractional distillation]], to separate mixtures into component parts. Helium is typically produced by separating it from [[natural gas]], and radon is isolated from the radioactive decay of radium compounds.<ref name="brit" /> The prices of the noble gases are influenced by their natural abundance, with argon being the cheapest and xenon the most expensive. As an example, the adjacent table lists the 2004 prices in the United States for laboratory quantities of each gas.

==Biological chemistry==

None of the elements in this group has any biological importance.<ref>{{cite journal |last1=Remick |first1=Kaleigh |last2=Helmann |first2=John D. |title=The Elements of Life: A Biocentric Tour of the Periodic Table |journal=Advances in Microbial Physiology |publisher=PubMed Central |date=30 January 2023 |volume=82 |pages=1–127 |doi=10.1016/bs.ampbs.2022.11.001 |pmid=36948652 |pmc=10727122 |isbn=978-0-443-19334-7 |quote=The group 18 elements (noble gases) are non-reactive and not biologically important.}}</ref>

==Applications==
[[File:Modern 3T MRI.JPG|thumb|left|Liquid helium is used to cool superconducting magnets in modern MRI scanners.|alt=A large solid cylinder with a hole in its center and a rail attached to its side.]]

<!-- cryogenics -->
Noble gases have very low boiling and melting points, which makes them useful as [[cryogenic]] [[refrigerant]]s.<ref>{{cite encyclopedia|title=Neon|encyclopedia=[[Encarta]]|year=2008}}</ref> In particular, [[liquid helium]], which boils at {{convert|4.2|K}}, is used for [[superconducting magnet]]s, such as those needed in [[nuclear magnetic resonance imaging]] and [[nuclear magnetic resonance]].<ref>{{cite journal|title=Demountable coaxial gas-cooled current leads for MRI superconducting magnets|author1=Zhang, C. J. |author2=Zhou, X. T. |author3=Yang, L. |journal=IEEE Transactions on Magnetics|publisher=[[IEEE]]|volume=28|issue=1|year=1992|pages=957–959|doi=10.1109/20.120038|bibcode= 1992ITM....28..957Z }}</ref> Liquid neon, although it does not reach temperatures as low as liquid helium, also finds use in cryogenics because it has over 40&nbsp;times more refrigerating capacity than liquid helium and over three times more than liquid hydrogen.<ref name=ullmann/>

<!-- diving -->
Helium is used as a component of [[breathing gases]] to replace nitrogen, due its low [[solubility]] in fluids, especially in [[lipids]]. Gases are absorbed by the [[blood]] and [[body tissue]]s when under pressure like in [[scuba diving]], which causes an [[anesthetic]] effect known as [[nitrogen narcosis]].<ref name=Fowler>{{cite journal |last1=Fowler |first1=B. |last2=Ackles |first2=K. N. |last3=Porlier |first3=G. |title=Effects of inert gas narcosis on behavior—a critical review |journal=Undersea Biomed. Res. |volume=12 |issue=4 |pages=369–402 |year=1985 |issn=0093-5387 |oclc=2068005 |pmid=4082343 |url=http://archive.rubicon-foundation.org/3019 |access-date=8 April 2008 |archive-url=https://web.archive.org/web/20101225052236/http://archive.rubicon-foundation.org/3019 |archive-date=25 December 2010 }}</ref> Due to its reduced solubility, little helium is taken into [[cell membranes]], and when helium is used to replace part of the breathing mixtures, such as in [[Trimix (breathing gas)|trimix]] or [[heliox]], a decrease in the narcotic effect of the gas at depth is obtained.<ref>{{harvnb|Bennett|1998|p=176}}</ref> Helium's reduced solubility offers further advantages for the condition known as [[Decompression sickness#Mechanism|decompression sickness]], or ''the bends''.<ref name="brit"/><ref>{{cite journal |editor-last=Vann|editor-first=R. D. |title=The Physiological Basis of Decompression|journal=38th Undersea and Hyperbaric Medical Society Workshop |volume=75(Phys)6-1-89 |year=1989 |page=437 |url=http://archive.rubicon-foundation.org/6853 |archive-url=https://web.archive.org/web/20081007192913/http://archive.rubicon-foundation.org/6853 |archive-date=7 October 2008 |access-date=31 May 2008}}</ref> The reduced amount of dissolved gas in the body means that fewer gas bubbles form during the decrease in pressure of the ascent. Another noble gas, argon, is considered the best option for use as a [[drysuit]] inflation gas for scuba diving.<ref>{{cite web |last=Maiken |first=Eric |title=Why Argon? |url=http://www.decompression.org/maiken/Why_Argon.htm |access-date=26 June 2008|publisher=Decompression|date=1 August 2004}}</ref> Helium is also used as filling gas in nuclear fuel rods for nuclear reactors.<ref>{{cite journal|last1=Horhoianu|first1=G.|title=Thermal behaviour of CANDU type fuel rods during steady state and transient operating conditions|journal=Annals of Nuclear Energy|volume=26|pages=1437–1445|year=1999|doi=10.1016/S0306-4549(99)00022-5|issue=16|last2=Ionescu|first2=D. V.|last3=Olteanu|first3=G.|bibcode=1999AnNuE..26.1437H }}</ref>

<!-- lifting -->
[[File:Goodyear-blimp.jpg|thumb|right|Goodyear Blimp|alt=Cigar-shaped blimp with "Good Year" written on its side.]]
Since the [[Hindenburg disaster|''Hindenburg'' disaster]] in 1937,<ref>{{cite news|title=Disaster Ascribed to Gas by Experts|work=[[The New York Times]]|date=7 May 1937|page=1}}</ref> helium has replaced hydrogen as a [[lifting gas]] in [[blimp]]s and [[balloon]]s: despite an 8.6%<ref>{{cite web
|last=Freudenrich|first=Craig|year=2008
|url=http://science.howstuffworks.com/blimp2.htm
|title=How Blimps Work|publisher=HowStuffWorks
|access-date=3 July 2008}}</ref> decrease in buoyancy compared to hydrogen, helium is not combustible.<ref name="brit"/>

<!-- scientific and some miscellaneous uses -->
In many applications, the noble gases are used to provide an inert atmosphere. Argon is used in the synthesis of [[air sensitive|air-sensitive compounds]] that are sensitive to nitrogen. Solid argon is also used for the study of very unstable compounds, such as [[reactive intermediate]]s, by trapping them in an inert [[matrix isolation|matrix]] at very low temperatures.<ref>{{cite journal |journal=Chem. Soc. Rev. |year=1980 |volume=9 |pages=1–23 |doi=10.1039/CS9800900001 |title=The matrix isolation technique and its application to organic chemistry |author=Dunkin, I. R.}}</ref> Helium is used as the carrier medium in [[gas chromatography]], as a filler gas for [[thermometers]], and in devices for measuring radiation, such as the [[Geiger counter]] and the [[bubble chamber]].<ref name=kirk/> Helium and argon are both commonly used to shield [[welding arc]]s and the surrounding [[base metal]] from the atmosphere during welding and cutting, as well as in other metallurgical processes and in the production of silicon for the semiconductor industry.<ref name="ullmann" />

<!-- lighting -->
[[File:Xenon short arc 1.jpg|thumb|left|15,000-watt [[xenon short-arc lamp]] used in [[IMAX]] projectors|alt=Elongated glass sphere with two metal rod electrodes inside, facing each other. One electrode is blunt and another is sharpened.]]
Noble gases are commonly used in [[lighting]] because of their lack of chemical reactivity. Argon, mixed with nitrogen, is used as a filler gas for [[incandescent light bulb]]s.<ref name=ullmann>{{cite book |author1=Häussinger, Peter |author2=Glatthaar, Reinhard |author3=Rhode, Wilhelm |author4=Kick, Helmut |author5=Benkmann, Christian |author6=Weber, Josef |author7=Wunschel, Hans-Jörg |author8=Stenke, Viktor |author9=Leicht, Edith |author10=Stenger, Hermann |chapter=Noble gases |title=Ullmann's Encyclopedia of Industrial Chemistry |publisher=Wiley |year=2002 |doi=10.1002/14356007.a17_485|isbn=3-527-30673-0 }}</ref> Krypton is used in high-performance light bulbs, which have higher [[color temperature]]s and greater efficiency, because it reduces the rate of evaporation of the filament more than argon; [[halogen lamps]], in particular, use krypton mixed with small amounts of compounds of [[iodine]] or [[bromine]].<ref name=ullmann/> The noble gases glow in distinctive colors when used inside [[gas-discharge lamp]]s, such as "[[neon lighting|neon lights]]". These lights are called after neon but often contain other gases and [[phosphor]]s, which add various hues to the orange-red color of neon. Xenon is commonly used in [[xenon arc lamp]]s, which, due to their nearly [[continuous spectrum]] that resembles daylight, find application in film projectors.<ref name=ullmann/>

<!-- lasers -->
The noble gases are used in [[excimer laser]]s, which are based on short-lived electronically excited molecules known as [[excimer]]s. The excimers used for lasers may be noble gas dimers such as Ar<sub>2</sub>, Kr<sub>2</sub> or Xe<sub>2</sub>, or more commonly, the noble gas is combined with a halogen in excimers such as ArF, KrF, XeF, or XeCl. These lasers produce [[ultraviolet]] light, which, due to its short [[wavelength]] (193 [[nanometer|nm]] for ArF and 248&nbsp;nm for KrF), allows for high-precision imaging. Excimer lasers have many industrial, medical, and scientific applications. They are used for [[microlithography]] and [[microfabrication]], which are essential for [[integrated circuit]] manufacture, and for [[laser surgery]], including laser [[angioplasty]] and [[eye surgery]].<ref>{{cite book |title=Excimer Laser Technology |author1=Basting, Dirk |author2=Marowsky, Gerd |publisher=Springer |year=2005 |isbn=3-540-20056-8}}</ref>

<!-- medical uses -->
Some noble gases have direct application in medicine. Helium is sometimes used to improve the ease of breathing of people with [[asthma]].<ref name=ullmann/> Xenon is used as an [[anesthetic]] because of its high solubility in lipids, which makes it more potent than the usual [[nitrous oxide]], and because it is readily eliminated from the body, resulting in faster recovery.<ref>{{cite journal|author1=Sanders, Robert D. |author2=Ma, Daqing |author3=Maze, Mervyn |title=Xenon: elemental anaesthesia in clinical practice|journal=British Medical Bulletin|year=2005|volume=71|issue=1|pages=115–135|doi= 10.1093/bmb/ldh034|pmid=15728132|doi-access=free}}</ref> Xenon finds application in medical imaging of the lungs through hyperpolarized MRI.<ref>{{cite journal|last1=Albert|first1=M. S.|last2=Balamore|first2=D.|title=Development of hyperpolarized noble gas MRI |journal=Nuclear Instruments and Methods in Physics Research A|year=1998|volume=402|pages=441–453|doi= 10.1016/S0168-9002(97)00888-7|pmid=11543065|issue=2–3|bibcode= 1998NIMPA.402..441A }}</ref> Radon, which is highly radioactive and is only available in minute amounts, is used in [[radiotherapy]].<ref name=brit />

<!-- ion engines -->
Noble gases, particularly xenon, are predominantly used in [[ion engines]] due to their inertness. Since ion engines are not driven by chemical reactions, chemically inert fuels are desired to prevent unwanted reaction between the fuel and anything else on the engine.

Oganesson is too unstable to work with and has no known application other than research.

=== Noble gases in Earth sciences application ===
The relative isotopic abundances of noble gases serve as an important [[Geochemical cycle|geochemical]] tracing tool in [[earth science]].<ref name=Mukhopadhyay-2019/><ref name="Burnard-2013">{{Cite book |url=http://link.springer.com/10.1007/978-3-642-28836-4 |title=The Noble Gases as Geochemical Tracers |date=2013 |publisher=Springer Berlin Heidelberg |isbn=978-3-642-28835-7 |editor-last=Burnard |editor-first=Pete |series=Advances in Isotope Geochemistry |location=Berlin, Heidelberg |language=en |doi=10.1007/978-3-642-28836-4|bibcode=2013nggt.book.....B }}</ref> They can unravel the Earth's degassing history and its effects to the surrounding environment (i.e., [[atmosphere]] composition<ref>{{Citation |last1=Ballentine |first1=Chris J. |title=13. Tracing Fluid Origin, Transport and Interaction in the Crust |date=2018-12-17 |pages=539–614 |url=https://www.degruyter.com/document/doi/10.1515/9781501509056-015/html |access-date=2024-09-23 |publisher=De Gruyter |language=en |doi=10.1515/9781501509056-015 |isbn=978-1-5015-0905-6 |last2=Burgess |first2=Ray |last3=Marty |first3=Bernard|url-access=subscription }}</ref>). Due to their inert nature and low abundances, change in the noble gas concentration and their isotopic ratios can be used to resolve and quantify the processes influencing their current signatures across [[Geology|geological]] settings.<ref name="Burnard-2013"/><ref name="Ballentine-2002b">{{Cite journal |last1=Ballentine |first1=C. J. |last2=Burnard |first2=P. G. |date=2002-01-01 |title=Production, Release and Transport of Noble Gases in the Continental Crust |url=https://pubs.geoscienceworld.org/rimg/article/47/1/481-538/235410 |journal=Reviews in Mineralogy and Geochemistry |language=en |volume=47 |issue=1 |pages=481–538 |doi=10.2138/rmg.2002.47.12 |bibcode=2002RvMG...47..481B |issn=1529-6466|url-access=subscription }}</ref>

====Helium====
[[Helium]] has two abundant isotopes: [[helium-3]], which is [[Primordial nuclide|primordial]] with high abundance in [[Internal structure of Earth|earth's core]] and [[Mantle (geology)|mantle]], and [[helium-4]], which originates from decay of [[radionuclide]]s (<sup>232</sup>Th, <sup>235,238</sup>U) abundant in the [[earth's crust]]. Isotopic ratios of helium are represented by R<sub>A</sub> value, a value relative to air measurement (<sup>3</sup>He/<sup>4</sup>He = 1.39*10<sup>−6</sup>).<ref name="Ozima-2002">{{Cite book |last1=Ozima |first1=Minoru |url=https://books.google.com/books?id=TMIAfSIe428C&pg=PP1 |title=Noble Gas Geochemistry |last2=Podosek |first2=Frank A. |date=2002 |publisher=Cambridge University Press |isbn=978-0-521-80366-3 |language=en}}</ref> [[Volatile (astrogeology)|Volatiles]] that originate from the earth's crust have a 0.02-0.05 R<sub>A</sub>, which indicate an enrichment of helium-4.<ref>{{Cite journal |last1=Ballentine |first1=Chris J. |last2=Sherwood Lollar |first2=Barbara |date=July 2002 |title=Regional groundwater focusing of nitrogen and noble gases into the Hugoton-Panhandle giant gas field, USA |url=https://linkinghub.elsevier.com/retrieve/pii/S0016703702008505 |journal=[[Geochimica et Cosmochimica Acta]] |language=en |volume=66 |issue=14 |pages=2483–2497 |doi=10.1016/S0016-7037(02)00850-5|bibcode=2002GeCoA..66.2483B |url-access=subscription }}</ref> Volatiles that originate from deeper sources such as [[subcontinental lithospheric mantle]] (SCLM), have a 6.1± 0.9 R<sub>A</sub><ref name="Gautheron-2002">{{Cite journal |last1=Gautheron |first1=Cécile |last2=Moreira |first2=Manuel |date=2002-05-30 |title=Helium signature of the subcontinental lithospheric mantle |url=https://linkinghub.elsevier.com/retrieve/pii/S0012821X02005630 |journal=Earth and Planetary Science Letters |volume=199 |issue=1 |pages=39–47 |doi=10.1016/S0012-821X(02)00563-0 |bibcode=2002E&PSL.199...39G |issn=0012-821X|url-access=subscription }}</ref> and mid-oceanic ridge basalts (MORB) display higher values (8 ± 1 R<sub>A</sub>).  [[Mantle plume]] samples have even higher values than > 8 R<sub>A</sub>.<ref name="Gautheron-2002" /><ref>{{Cite journal |last=Graham |first=D. W. |date=2002-01-01 |title=Noble Gas Isotope Geochemistry of Mid-Ocean Ridge and Ocean Island Basalts: Characterization of Mantle Source Reservoirs |url=https://pubs.geoscienceworld.org/rimg/article/47/1/247-317/235393 |journal=Reviews in Mineralogy and Geochemistry |language=en |volume=47 |issue=1 |pages=247–317 |doi=10.2138/rmg.2002.47.8 |bibcode=2002RvMG...47..247G |issn=1529-6466|url-access=subscription }}</ref>  [[Solar wind]], which represent an unmodified [[Primordial nuclide|primordial]] signature is reported to have ~ 330 R<sub>A</sub>.<ref>{{Cite journal |last1=Benkert |first1=Jean-Paul |last2=Baur |first2=Heinrich |last3=Signer |first3=Peter |last4=Wieler |first4=Rainer |date=1993-07-25 |title=He, Ne, and Ar from the solar wind and solar energetic particles in lunar ilmenites and pyroxenes |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/93JE01460 |journal=Journal of Geophysical Research: Planets |language=en |volume=98 |issue=E7 |pages=13147–13162 |doi=10.1029/93JE01460 |bibcode=1993JGR....9813147B |issn=0148-0227|url-access=subscription }}</ref>

====Neon====
[[Neon]] has three main stable isotopes:<sup>20</sup>Ne, <sup>21</sup>Ne and <sup>22</sup>Ne, with <sup>20</sup>Ne produced by cosmic [[nucleogenic]] reactions, causing high abundance in the atmosphere.<ref name="Ballentine-2002b"/><ref name="Wetherill 679–683">{{Cite journal |last=Wetherill |first=George W. |date=1954-11-01 |title=Variations in the Isotopic Abundances of Neon and Argon Extracted from Radioactive Minerals |url=https://journals.aps.org/pr/abstract/10.1103/PhysRev.96.679 |journal=Physical Review |volume=96 |issue=3 |pages=679–683 |doi=10.1103/PhysRev.96.679|bibcode=1954PhRv...96..679W }}</ref> <sup>21</sup>Ne and <sup>22</sup>Ne are produced in the earth's crust as a result of interactions between alpha and neutron particles with light elements; <sup>18</sup>O, <sup>19</sup>F and <sup>24,25</sup>Mg.<ref>{{Cite journal |last1=Yatsevich |first1=Igor |last2=Honda |first2=Masahiko |date=1997-05-10 |title=Production of nucleogenic neon in the Earth from natural radioactive decay |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/97JB00395 |journal=Journal of Geophysical Research: Solid Earth |language=en |volume=102 |issue=B5 |pages=10291–10298 |doi=10.1029/97JB00395 |bibcode=1997JGR...10210291Y |issn=0148-0227|url-access=subscription }}</ref> The neon ratios (<sup>20</sup>Ne/<sup>22</sup>Ne and <sup>21</sup>Ne/<sup>22</sup>Ne) are systematically used to discern the heterogeneity in the [[Mantle (geology)|Earth's mantle]] and volatile sources. Complimenting He isotope data, neon isotope data additionally provide insight to thermal evolution of Earth's systems.<ref>{{Cite journal |last1=Tremblay |first1=Marissa M. |last2=Shuster |first2=David L. |last3=Balco |first3=Greg |last4=Cassata |first4=William S. |date=2017-05-15 |title=Neon diffusion kinetics and implications for cosmogenic neon paleothermometry in feldspars |url=https://linkinghub.elsevier.com/retrieve/pii/S001670371730090X |journal=Geochimica et Cosmochimica Acta |volume=205 |pages=14–30 |doi=10.1016/j.gca.2017.02.013 |bibcode=2017GeCoA.205...14T |issn=0016-7037}}</ref>       
{| class="wikitable"
|+
!<sup>20</sup>Ne/<sup>22</sup>Ne
!<sup>21</sup>Ne/<sup>22</sup>Ne
!Endmember
|-
|9.8
|0.029
|Air<ref name="Ballentine-2002a">{{Cite journal |last1=Ballentine |first1=C. J. |last2=Burnard |first2=P. G. |date=2002-01-01 |title=Production, Release and Transport of Noble Gases in the Continental Crust |url=https://pubs.geoscienceworld.org/rimg/article/47/1/481-538/235410 |journal=Reviews in Mineralogy and Geochemistry |language=en |volume=47 |issue=1 |pages=481–538 |bibcode=2002RvMG...47..481B |doi=10.2138/rmg.2002.47.12 |issn=1529-6466|url-access=subscription }}</ref>
|-
|12.5
|0.0677
|MORB<ref>{{Cite journal |last1=Gilfillan |first1=Stuart M. V. |last2=Ballentine |first2=Chris J. |last3=Holland |first3=Greg |last4=Blagburn |first4=Dave |last5=Lollar |first5=Barbara Sherwood |last6=Stevens |first6=Scott |last7=Schoell |first7=Martin |last8=Cassidy |first8=Martin |date=2008-02-15 |title=The noble gas geochemistry of natural CO2 gas reservoirs from the Colorado Plateau and Rocky Mountain provinces, USA |url=https://linkinghub.elsevier.com/retrieve/pii/S0016703707005807 |journal=Geochimica et Cosmochimica Acta |volume=72 |issue=4 |pages=1174–1198 |doi=10.1016/j.gca.2007.10.009 |issn=0016-7037|url-access=subscription }}</ref>
|-
|13.81
|0.0330
|Solar Wind<ref>{{Cite journal |last1=Grimberg |first1=Ansgar |last2=Baur |first2=Heinrich |last3=Bühler |first3=Fritz |last4=Bochsler |first4=Peter |last5=Wieler |first5=Rainer |date=2008-01-15 |title=Solar wind helium, neon, and argon isotopic and elemental composition: Data from the metallic glass flown on NASA's Genesis mission |url=https://linkinghub.elsevier.com/retrieve/pii/S0016703707005996 |journal=Geochimica et Cosmochimica Acta |volume=72 |issue=2 |pages=626–645 |doi=10.1016/j.gca.2007.10.017 |bibcode=2008GeCoA..72..626G |issn=0016-7037|url-access=subscription }}</ref>
|-
|0
|3.30±0.2
|Archean Crust<ref>{{Cite journal |last1=Lippmann-Pipke |first1=Johanna |last2=Sherwood Lollar |first2=Barbara |last3=Niedermann |first3=Samuel |last4=Stroncik |first4=Nicole A. |last5=Naumann |first5=Rudolf |last6=van Heerden |first6=Esta |last7=Onstott |first7=Tullis C. |date=2011-04-22 |title=Neon identifies two billion year old fluid component in Kaapvaal Craton |url=https://linkinghub.elsevier.com/retrieve/pii/S0009254111000544 |journal=Chemical Geology |volume=283 |issue=3 |pages=287–296 |doi=10.1016/j.chemgeo.2011.01.028 |bibcode=2011ChGeo.283..287L |issn=0009-2541|url-access=subscription }}</ref>
|-
|0
|0.47
|Precambrian Crust<ref>{{Cite journal |last1=Kennedy |first1=B. M. |last2=Hiyagon |first2=H. |last3=Reynolds |first3=J. H. |date=1990-06-01 |title=Crustal neon: a striking uniformity |url=https://linkinghub.elsevier.com/retrieve/pii/0012821X90900302 |journal=Earth and Planetary Science Letters |volume=98 |issue=3 |pages=277–286 |doi=10.1016/0012-821X(90)90030-2 |bibcode=1990E&PSL..98..277K |issn=0012-821X|url-access=subscription }}</ref>
|}

==== Argon ====
[[Isotopes of argon|Argon]] has three stable isotopes: <sup>36</sup>Ar, <sup>38</sup>Ar and <sup>40</sup>Ar. <sup>36</sup>Ar and <sup>38</sup>Ar are [[Primordial nuclide|primordial]], with their inventory on the earth's crust dependent on the equilibration of [[meteoric water]] with the crustal fluids.<ref name="Ballentine-2002b"/> This explains huge inventory of <sup>36</sup>Ar in the atmosphere. Production of these two isotopes (<sup>36</sup>Ar and <sup>38</sup>Ar) is negligible within the earth's crust, only limited concentrations of <sup>38</sup>Ar can be produced by interaction between alpha particles from decay of <sup>235,238</sup>U and <sup>232</sup>Th and light elements (<sup>37</sup>Cl and <sup>41</sup>K). While <sup>36</sup>Ar is continuously being produced by Beta-decay of <sup>36</sup>Cl.<ref name="Wetherill 679–683"/><ref>{{Cite journal |last1=Fleming |first1=W. H. |last2=Thode |first2=H. G. |date=1953-10-15 |title=Neutron and Spontaneous Fission in Uranium Ores |url=https://link.aps.org/doi/10.1103/PhysRev.92.378 |journal=Physical Review |language=en |volume=92 |issue=2 |pages=378–382 |doi=10.1103/PhysRev.92.378 |bibcode=1953PhRv...92..378F |issn=0031-899X|url-access=subscription }}</ref> <sup>40</sup>Ar is a product of radiogenic decay of <sup>40</sup>K. Different endmembers values for <sup>40</sup>Ar/<sup>36</sup>Ar have been reported; Air = 295.5,<ref name="Burnard-1997">{{Cite journal |last1=Burnard |first1=Pete |last2=Graham |first2=David |last3=Turner |first3=Grenville |date=1997-04-25 |title=Vesicle-Specific Noble Gas Analyses of "Popping Rock": Implications for Primordial Noble Gases in Earth |journal=Science |volume=276 |issue=5312 |pages=568–571 |doi=10.1126/science.276.5312.568 |pmid=9110971 |issn=0036-8075}}</ref> MORB = 40,000,<ref name="Burnard-1997" /> and crust = 3000.<ref name="Ballentine-2002b"/>

====Krypton====
[[Krypton]] has several [[Isotopes of krypton|isotopes]], with <sup>78, 80, 82</sup>Kr being [[Primordial nuclide|primordial]], while <sup>83,84, 86</sup>Kr results from spontaneous fission of <sup>244</sup>Pu and radiogenic decay of <sup>238</sup>U.<ref name=Mukhopadhyay-2019>{{Cite journal |last1=Mukhopadhyay |first1=Sujoy |last2=Parai |first2=Rita |date=2019-05-30 |title=Noble Gases: A Record of Earth's Evolution and Mantle Dynamics |url=https://www.annualreviews.org/doi/10.1146/annurev-earth-053018-060238 |journal=Annual Review of Earth and Planetary Sciences |language=en |volume=47 |issue=1 |pages=389–419 |doi=10.1146/annurev-earth-053018-060238 |bibcode=2019AREPS..47..389M |issn=0084-6597}}</ref><ref name="Ballentine-2002b"/> Krypton's isotopes geochemical signature in mantle reservoirs resembling the modern atmosphere. preserves the solar-like primordial signature.<ref name="Holland-2006">{{Cite journal |last1=Holland |first1=Greg |last2=Ballentine |first2=Chris J. |date=May 2006 |title=Seawater subduction controls the heavy noble gas composition of the mantle |url=https://www.nature.com/articles/nature04761 |journal=Nature |language=en |volume=441 |issue=7090 |pages=186–191 |doi=10.1038/nature04761 |pmid=16688169 |bibcode=2006Natur.441..186H |issn=0028-0836|url-access=subscription }}</ref> Krypton isotopes have been used to decipher the mechanism of volatiles delivery to earth's system, which had great implication to evolution of earth (nitrogen, oxygen, and oxygen) and emergence of life.<ref>{{Cite journal |last1=Péron |first1=Sandrine |last2=Mukhopadhyay |first2=Sujoy |last3=Kurz |first3=Mark D. |last4=Graham |first4=David W. |date=December 2021 |title=Deep-mantle krypton reveals Earth's early accretion of carbonaceous matter |url=https://www.nature.com/articles/s41586-021-04092-z |journal=Nature |language=en |volume=600 |issue=7889 |pages=462–467 |doi=10.1038/s41586-021-04092-z |pmid=34912082 |bibcode=2021Natur.600..462P |issn=1476-4687|url-access=subscription }}</ref> This is largely due to a clear distinction of krypton isotope signature from various sources such as [[Chondrite|chondritic material]], [[solar wind]] and [[comet]]ary.<ref>{{Cite journal |last=Marty |first=Bernard |date=2012-01-01 |title=The origins and concentrations of water, carbon, nitrogen and noble gases on Earth |url=https://linkinghub.elsevier.com/retrieve/pii/S0012821X11006388 |journal=Earth and Planetary Science Letters |volume=313–314 |pages=56–66 |doi=10.1016/j.epsl.2011.10.040 |arxiv=1405.6336 |bibcode=2012E&PSL.313...56M |issn=0012-821X}}</ref><ref>{{Cite journal |last1=Marty |first1=B. |last2=Altwegg |first2=K. |last3=Balsiger |first3=H. |last4=Bar-Nun |first4=A. |last5=Bekaert |first5=D. V. |last6=Berthelier |first6=J.-J. |last7=Bieler |first7=A. |last8=Briois |first8=C. |last9=Calmonte |first9=U. |last10=Combi |first10=M. |last11=De Keyser |first11=J. |last12=Fiethe |first12=B. |last13=Fuselier |first13=S. A. |last14=Gasc |first14=S. |last15=Gombosi |first15=T. I. |date=2017-06-09 |title=Xenon isotopes in 67P/Churyumov-Gerasimenko show that comets contributed to Earth's atmosphere |url=https://www.science.org/doi/10.1126/science.aal3496 |journal=Science |language=en |volume=356 |issue=6342 |pages=1069–1072 |doi=10.1126/science.aal3496 |pmid=28596364 |bibcode=2017Sci...356.1069M |issn=0036-8075}}</ref>

====Xenon====
{{main|Xenon isotope geochemistry}}
[[Xenon]] has [[Isotopes of xenon|nine isotopes]], most of which are produced by the [[radiogenic decay]]. Krypton and xenon noble gases requires pristine, robust geochemical sampling protocol to avoid atmospheric contamination.<ref>{{Cite journal |last1=Farley |first1=K. A. |last2=Neroda |first2=E. |date=May 1998 |title=Noble Gases in the Earth's Mantle |url=https://www.annualreviews.org/doi/10.1146/annurev.earth.26.1.189 |journal=Annual Review of Earth and Planetary Sciences |language=en |volume=26 |issue=1 |pages=189–218 |doi=10.1146/annurev.earth.26.1.189 |bibcode=1998AREPS..26..189F |issn=0084-6597|url-access=subscription }}</ref> Furthermore, sophisticated instrumentation is required to resolve mass peaks among many isotopes with narrow mass difference during analysis.   
{| class="wikitable"
!<sup>129</sup>Xe/<sup>130</sup>Xe
!Endmember
|-
|6,496
|Air
|-
|7.7<ref>{{Cite journal |last1=Moreira |first1=Manuel |last2=Kunz |first2=Joachim |last3=Allègre |first3=Claude |date=1998-02-20 |title=Rare Gas Systematics in Popping Rock: Isotopic and Elemental Compositions in the Upper Mantle |url=https://www.science.org/doi/10.1126/science.279.5354.1178 |journal=Science |language=en |volume=279 |issue=5354 |pages=1178–1181 |doi=10.1126/science.279.5354.1178 |pmid=9469801 |bibcode=1998Sci...279.1178M |issn=0036-8075|url-access=subscription }}</ref>
|MORB
|-
|6.7<ref>{{Cite journal |last1=Raquin |first1=Aude |last2=Moreira |first2=Manuel |date=2009-10-15 |title=Atmospheric 38Ar/36Ar in the mantle: Implications for the nature of the terrestrial parent bodies |url=https://linkinghub.elsevier.com/retrieve/pii/S0012821X09005275 |journal=Earth and Planetary Science Letters |volume=287 |issue=3 |pages=551–558 |doi=10.1016/j.epsl.2009.09.003 |issn=0012-821X|url-access=subscription }}</ref>
|OIB Galapagos
|-
|6.8<ref>{{Cite journal |last1=Füri |first1=Evelyn |last2=Hilton |first2=D. R. |last3=Halldórsson |first3=S. A. |last4=Barry |first4=P. H. |last5=Hahm |first5=D. |last6=Fischer |first6=T. P. |last7=Grönvold |first7=K. |date=2010-06-01 |title=Apparent decoupling of the He and Ne isotope systematics of the Icelandic mantle: The role of He depletion, melt mixing, degassing fractionation and air interaction |url=https://linkinghub.elsevier.com/retrieve/pii/S001670371000150X |journal=Geochimica et Cosmochimica Acta |volume=74 |issue=11 |pages=3307–3332 |doi=10.1016/j.gca.2010.03.023 |bibcode=2010GeCoA..74.3307F |issn=0016-7037|url-access=subscription }}</ref>
|OIB Icelands
|}

==== Sampling of noble gases ====
Noble gas measurements can be obtained from sources like [[volcanic vents]], [[Hot spring|springs]], and [[geothermal wells]] following specific sampling protocols.<ref>{{Cite journal |last1=Hilton |first1=D. R. |last2=Fischer |first2=T. P. |last3=Marty |first3=B. |date=2002-01-01 |title=Noble Gases and Volatile Recycling at Subduction Zones |url=https://pubs.geoscienceworld.org/rimg/article/47/1/319-370/235395 |journal=Reviews in Mineralogy and Geochemistry |language=en |volume=47 |issue=1 |pages=319–370 |doi=10.2138/rmg.2002.47.9 |bibcode=2002RvMG...47..319H |issn=1529-6466|url-access=subscription }}</ref> The classic specific sampling protocol include the following.
* Copper tubes - These are standard refrigeration copper tubes, cut to ~10&nbsp;cm<sup>3</sup> with a 3/8" outer diameter, and are used for sampling volatile discharges by connecting an inverted funnel to the tube via TygonⓇ tubing, ensuring one-way inflow and preventing air contamination. Their malleability allows for cold welding or pinching off to seal the ends after sufficient flushing with the sample.
** [[File:Giggenbach_Bottle.jpg|thumb|Sampling of noble gases using a Giggenbach bottle, a funnel is placed on top of the hot spring to focus the stream of sample towards the bottle via the Tygon tube. A geochemist is controlling the flow of the sample inlet using a Teflon valve. Note the condensation process inside the evacuated Giggenbach bottle.]]Giggenbach bottles – Giggenbach bottles are evacuated glass flasks with a Teflon stopcock, used for sampling and storing gases. They require pre-evacuation before sampling, as noble gases accumulate in the headspace.<ref>{{Cite web |title=Methods for the collection and analysis of geothermal and volcanic water and gas samples |url=https://search.worldcat.org/title/316795976 |access-date=2024-10-19 |website=search.worldcat.org |language=en}}</ref> These bottles were first invented and distributed by a Werner F. Giggenbach, a German chemist.<ref>{{Cite journal |last=Giggenbach |first=W. F. |date=1975-03-01 |title=A simple method for the collection and analysis of volcanic gas samples |url=https://link.springer.com/article/10.1007/BF02596953 |journal=Bulletin Volcanologique |language=en |volume=39 |issue=1 |pages=132–145 |doi=10.1007/BF02596953 |bibcode=1975BVol...39..132G |issn=1432-0819|url-access=subscription }}</ref>

===== Analysis of noble gases =====
Noble gases have numerous isotopes and subtle mass variation that requires high-precision detection systems.  Originally, scientists used [[magnetic sector mass spectrometry]], which is time-consuming and has low sensitivity due to "peak jumping mode".<ref>{{Cite journal |url=https://pubs.aip.org/rsi/article/27/11/928/299004/High-Sensitivity-Mass-Spectrometer-for-Noble-Gas |access-date=2024-10-16 |journal=Review of Scientific Instruments |doi=10.1063/1.1715415 |title=High Sensitivity Mass Spectrometer for Noble Gas Analysis |date=1956 |last1=Reynolds |first1=John H. |volume=27 |issue=11 |pages=928–934 |bibcode=1956RScI...27..928R |url-access=subscription }}</ref><ref name="Mark-2009">{{Cite journal |last1=Mark |first1=D. F. |last2=Barfod |first2=D. |last3=Stuart |first3=F. M. |last4=Imlach |first4=J. |date=October 2009 |title=The ARGUS multicollector noble gas mass spectrometer: Performance for 40 Ar/ 39 Ar geochronology |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2009GC002643 |journal=Geochemistry, Geophysics, Geosystems |language=en |volume=10 |issue=10 |doi=10.1029/2009GC002643 |issn=1525-2027|url-access=subscription }}</ref> Multiple-collector mass spectrometers, like [[Quadrupole mass analyzer|Quadrupole mass spectrometers]] (QMS), enable simultaneous detection of isotopes, improving sensitivity and throughput.<ref name="Mark-2009" /> Before analysis, sample preparation is essential due to the low abundance of noble gases, involving extraction, purification system.<ref name="Burnard-2013"/> Extraction allows liberation of noble gases from their carrier (major phase; fluid or solid) while purification remove impurities and improve concentration per unit sample volume.<ref name="Mtili-2021">{{Cite journal |last1=Mtili |first1=K. M. |last2=Byrne |first2=D. J. |last3=Tyne |first3=R. L. |last4=Kazimoto |first4=E. O. |last5=Kimani |first5=C. N. |last6=Kasanzu |first6=C. H. |last7=Hillegonds |first7=D. J. |last8=Ballentine |first8=C. J. |last9=Barry |first9=P. H. |date=2021-12-20 |title=The origin of high helium concentrations in the gas fields of southwestern Tanzania |url=https://linkinghub.elsevier.com/retrieve/pii/S000925412100485X |journal=Chemical Geology |volume=585 |article-number=120542 |doi=10.1016/j.chemgeo.2021.120542 |bibcode=2021ChGeo.58520542M |issn=0009-2541|url-access=subscription }}</ref> Cryogenic traps are used for sequential analysis without peak interference by stepwise temperature raise.<ref name="Li-2021">{{Cite journal |last1=Li |first1=Yan |last2=Tootell |first2=Damian |last3=Holland |first3=Greg |last4=Zhou |first4=Zheng |date=November 2021 |title=Performance of the NGX High-Resolution Multiple Collector Noble Gas Mass Spectrometer |journal=Geochemistry, Geophysics, Geosystems |language=en |volume=22 |issue=11 |doi=10.1029/2021GC009997 |bibcode=2021GGG....2209997L |issn=1525-2027|doi-access=free }}</ref>

Research labs have successfully developed miniaturized field-based mass spectrometers, which can analyze noble gases with an analytical uncertainty of 1–3% using low-cost vacuum systems and quadrupole mass analyzers.<ref>{{Cite journal |last1=Brennwald |first1=Matthias S. |last2=Schmidt |first2=Mark |last3=Oser |first3=Julian |last4=Kipfer |first4=Rolf |date=2016-12-20 |title=A Portable and Autonomous Mass Spectrometric System for On-Site Environmental Gas Analysis |url=https://pubs.acs.org/doi/10.1021/acs.est.6b03669 |journal=Environmental Science & Technology |language=en |volume=50 |issue=24 |pages=13455–13463 |doi=10.1021/acs.est.6b03669 |pmid=27993051 |bibcode=2016EnST...5013455B |issn=0013-936X|url-access=subscription }}</ref> [[File:Gchron.copernicus.org.jpg|thumb|Extraction and purification (clean up) mass spectrometer line.]]

==Discharge color==

{| class="wikitable" style="text-align:center;margin:1em auto"
|+ Colors and spectra (bottom row) of electric discharge in noble gases; only the second row represents pure gases.
| width="20%"|[[File:Helium-glow.jpg|alt=Glass tube shining violet light with a wire wound over it|120px]]
| width="20%"|[[File:Neon-glow.jpg|alt=Glass tube shining orange light with a wire wound over it|120px]]
| width="20%"|[[File:Argon-glow.jpg|alt=Glass tube shining purple light with a wire wound over it|120px]]
| width="20%"|[[File:Krypton-glow.jpg|alt=Glass tube shining white light with a wire wound over it|120px]]
| width="20%"|[[File:Xenon-glow.jpg|alt=Glass tube shining blue light with a wire wound over it|120px]]
|-
| width="20%"|[[File:Helium discharge tube.jpg|alt=Glass tube shining light red|120px]]
| width="20%"|[[File:Neon discharge tube.jpg|alt=Glass tube shining reddish-orange|120px]]
| width="20%"|[[File:Argon discharge tube.jpg|alt=Glass tube shining purple|120px]]
| width="20%"|[[File:Krypton discharge tube.jpg|alt=Glass tube shining bluish-white|120px]]
| width="20%"|[[File:Xenon discharge tube.jpg|alt=Glass tube shining bluish-violet|120px]]
|-
| width="20%"|[[File:HeTube.jpg|alt=Illuminated light red gas discharge tubes shaped as letters H and e|120px]]
| width="20%"|[[File:NeTube.jpg|alt=Illuminated orange gas discharge tubes shaped as letters N and e|120px]]
| width="20%"|[[File:ArTube.jpg|alt=Illuminated light blue gas discharge tubes shaped as letters A and r|120px]]
| width="20%"|[[File:KrTube.jpg|alt=Illuminated white gas discharge tubes shaped as letters K and r|120px]]
| width="20%"|[[File:XeTube.jpg|alt=Illuminated violet gas discharge tubes shaped as letters X and e|120px]]
|-
| width="20%"|[[File:Helium spectra.jpg|alt=Helium line spectrum|120px]]
| width="20%"|[[File:Neon spectra.jpg|alt=Neon line spectrum|120px]]
| width="20%"|[[File:Argon Spectrum.png|alt=Argon line spectrum|120px]]
| width="20%"|[[File:Krypton Spectrum.jpg|alt=Krypton line spectrum|120px]]
| width="20%"|[[File:Xenon Spectrum.jpg|alt=Xenon line spectrum|120px]]
|-
|[[Helium]]
|[[Neon]]
|[[Argon]]
|[[Krypton]]
|[[Xenon]]
|}

The color of gas discharge emission depends on several factors, including the following:<ref>{{cite book|pages=383–384|url=https://books.google.com/books?id=AEFPNfghI3QC&pg=PA383|title=Scientific photography and applied imaging|author=Ray, Sidney F.|publisher=Focal Press|year=1999|isbn=0-240-51323-1}}</ref>

* discharge parameters (local value of [[current density]] and [[electric field]], temperature, etc. – note the color variation along the discharge in the top row);
* gas purity (even small fraction of certain gases can affect color);
* material of the discharge tube envelope – note suppression of the UV and blue components in the bottom-row tubes made of thick household glass.

==See also==
*[[Noble gas (data page)]], for extended tables of physical properties.
*[[Noble metal]], for metals that are resistant to corrosion or oxidation.
*[[Inert gas]], for any gas that is not reactive under normal circumstances.
*[[Industrial gas]]
*[[Octet rule]]

==Notes==
{{Reflist|30em}}

==References==
{{Library resources box
 |onlinebooks=yes
 |by=no
 |lcheading= Gases, Rare
 |label=Noble gas
 }}
{{Commons category|Noble gases}}
{{Wiktionary}}
{{Wikibooks}}
{{Wikiversity|Noble gases}}

* {{cite book|title=The Physiology and Medicine of Diving|last1= Bennett|first1= Peter B.|last2= Elliott|first2=David H.|publisher=[[SPCK Publishing]] |year=1998|isbn=0-7020-2410-4|ref=CITEREFBennett1998}}
* {{cite book|author=Bobrow Test Preparation Services|title=CliffsAP Chemistry|publisher=[[CliffsNotes]]|date=5 December 2007|isbn=978-0-470-13500-6|ref=CITEREFCliffsNotes2007}}
* {{cite book|last1=Greenwood |first1= N. N. |last2=Earnshaw|first2=A.|title=Chemistry of the Elements |edition= 2nd |publisher=Oxford:Butterworth-Heinemann|year=1997|isbn=0-7506-3365-4|ref=CITEREFGreenwood1997}}
* {{cite book|last1=Harding|first1=Charlie J.|last2=Janes|first2=Rob|year=2002|title=Elements of the P Block|publisher=[[Royal Society of Chemistry]]|isbn= 0-85404-690-9 |ref=CITEREFHarding2002}}
* {{cite book|last= Holloway|first= John H.|year= 1968|title= Noble-Gas Chemistry|publisher= [[Methuen Publishing]]|location= [[London]]|isbn= 0-412-21100-9|url-access= registration|url= https://archive.org/details/trent_0116400178434}}
* {{cite book|last=Mendeleev|first=D.|author-link=Dmitri Mendeleev|title= Osnovy Khimii (The Principles of Chemistry)|edition=7th|date=1902–1903|publisher=Collier |location=New York |language=ru|url=https://archive.org/details/principlesofchem00menduoft|ref=CITEREFMendeleev1903}}
* {{cite book|first1=Minoru|last1=Ozima|last2=Podosek|first2=Frank A.|title=Noble Gas Geochemistry|year=2002|publisher=[[Cambridge University Press]]|isbn=0-521-80366-7|ref=CITEREFOzima2002}}
* {{cite book|last1=Weinhold|first1=F.|last2=Landis|first2=C.|title=Valency and bonding|publisher=[[Cambridge University Press]]|year=2005|isbn=0-521-83128-8|ref=CITEREFWeinhold2005}}

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