Editing Noble gas (section)

==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|url-status = dead|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]].