Editing Radon (section)

== Characteristics ==
[[File:Radon spectrum.png|thumb|left|upright=0.85|[[Emission spectrum]] of radon, photographed by [[Ernest Rutherford]] in 1908. Numbers at the side of the spectrum are wavelengths. The middle spectrum is of radium emanation (radon), while the outer two are of [[helium]] (added to calibrate the wavelengths).]]

=== Physical properties ===
[[File:Radon decay in a cloud chamber.jpg|thumb|Radon in a cloud chamber showing its radiation]]
Radon is a colorless, odorless, and tasteless<ref name="guide">{{cite web |date=2016 |title=A Citizen's Guide to Radon: The Guide to Protecting Yourself and Your Family from Radon |url=https://www.epa.gov/radon/citizens-guide-radon-guide-protecting-yourself-and-your-family-radon |publisher=Environmental Protection Agency}}</ref> gas and therefore is not detectable by human senses alone. At [[standard temperature and pressure]], it forms a [[monatomic gas]] with a density of 9.73&nbsp;kg/m<sup>3</sup>, about 8 times the density of the [[Atmosphere of Earth|Earth's atmosphere]] at sea level, 1.217&nbsp;kg/m<sup>3</sup>.<ref>{{cite web |last=Williams |first=David R. |date=2007-04-19 |title=Earth Fact Sheet |publisher=[[NASA]] |url=http://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html |access-date=2008-06-26}}</ref> It is one of the densest gases at room temperature (a few are denser, e.g. [[perfluorobutane|CF<sub>3</sub>(CF<sub>2</sub>)<sub>2</sub>CF<sub>3</sub>]] and [[tungsten hexafluoride|WF<sub>6</sub>]]) and is the densest of the noble gases. Although colorless at standard temperature and pressure, when cooled below its [[freezing point]] of {{convert|202|K}}, it emits a brilliant [[radioluminescence]] that turns from yellow to orange-red as the temperature lowers.<ref>{{cite web |title=The Element Radon|website = It's Elemental |url=http://education.jlab.org/itselemental/ele086.html |access-date= |publisher=Jefferson Lab}}</ref> Upon [[condensation]], it glows because of the intense radiation it produces.<ref>{{cite book |last=Thomas |first=Jens |date= 2002 |title= Noble Gases |publisher=Marshall Cavendish |isbn=978-0-7614-1462-9 |page=13 |url=https://books.google.com/books?id=T0Iiv0BJ1E0C&pg=PA13}}</ref> It is sparingly [[soluble]] in water, but more soluble than lighter noble gases. It is appreciably more soluble in [[organic liquid]]s than in water. Its solubility equation is as follows:<ref>{{Unbulleted list citebundle|{{cite book |last1=Gerrard |first1=W |title=Solubility Data Series |date=1979 |publisher=Pergamon Press |pages=264–271 |edition=Vol.2 |url= https://iupac.github.io/SolubilityDataSeries/volumes/SDS-2.pdf }}|{{cite book |last1=Battino |first1=R |title=Solubility Data Series |date=1979 |publisher= Pergamon Press |pages=227–234 |edition=Vol.2 |url=https://iupac.github.io/SolubilityDataSeries/volumes/SDS-2.pdf }}|{{cite journal |last1=Saito |first1=M |title=''Determination of Radon Solubilities to 1,2-Dimethylbenzene, 1,3- Dimethylbenzene, 1,4-Dime thylbenzene, 1,3,5-Trimethylbenzene, 1, 2,4-Trimethylbenzene and 1-Isopropyl-4-methylbenzene'' |journal=Nippon Kagaku Kaishi |date=1999 |issue=6 |pages=363–368|doi=10.1246/nikkashi.1999.363 |url=https://www.jstage.jst.go.jp/article/nikkashi1972/1999/6/1999_6_363/_article/download/-char/ja|doi-access=free }}}}</ref>

: <math>\chi = \exp(B/T-A)</math>

where <math>\chi</math> is the molar fraction of radon, <math>T</math> is the absolute temperature, and <math>A</math> and <math>B</math> are solvent constants.

=== Chemical properties ===
Radon is a member of the zero-[[Valence (chemistry)|valence]] elements that are called noble gases, and is chemically not very [[Reactivity (chemistry)|reactive]]. The [[inert pair effect]] stabilizes the 6s shell, making it unavailable for bonding—a consequence only understood within [[relativistic quantum chemistry]].<ref name="Thayer" />{{rp|66}} The 3.8-day half-life of {{sup|222}}Rn makes it useful in physical sciences as a natural [[Radioactive tracer|tracer]]. Because radon is a gas at standard conditions, unlike its decay-chain parents, it can readily be extracted from them for research.<ref name="Ullmann" />

It is [[Inert gas|inert]] to most common chemical reactions, such as [[combustion]], because the outer [[valence shell]] contains eight [[electron]]s. This produces a stable, minimum energy configuration in which the outer electrons are tightly bound.<ref>{{cite web |last=Bader |first=Richard F. W. |url=http://miranda.chemistry.mcmaster.ca/esam/ |title=An Introduction to the Electronic Structure of Atoms and Molecules |publisher=[[McMaster University]] |access-date=2008-06-26}}</ref> Its [[first ionization energy]]—the minimum energy required to extract one electron from it—is 1037&nbsp;kJ/mol.<ref>{{cite book |author=David R. Lide |title=CRC Handbook of Chemistry and Physics |edition=84th|publisher=CRC Press|location=Boca Raton, Florida|date=2003|chapter=Section 10, Atomic, Molecular, and Optical Physics; Ionization Potentials of Atoms and Atomic Ions}}</ref> In accordance with [[Periodic table|periodic trends]], radon has a lower [[electronegativity]] than the element one period before it, [[xenon]], and is therefore more reactive. Early studies concluded that the stability of radon [[hydrate]] should be of the same order as that of the hydrates of [[chlorine]] ({{chem|Cl|2}}) or [[sulfur dioxide]] ({{chem|SO|2}}), and significantly higher than the stability of the hydrate of [[hydrogen sulfide]] ({{chem|H|2|S}}).<ref>{{cite journal |doi=10.1070/RC1982v051n01ABEH002787 |title=The Chemistry of Radon |date=1982 |author=Avrorin, V. V. |journal=[[Russian Chemical Reviews]] |volume=51 |issue=1 |page=12 |last2=Krasikova |first2=R. N. |last3=Nefedov |first3=V. D. |last4=Toropova |first4=M. A. |bibcode = 1982RuCRv..51...12A|s2cid=250906059 }}</ref>

Because of its cost and radioactivity, experimental chemical research is seldom performed with radon, and as a result there are very few reported compounds of radon, all either [[fluoride]]s or [[oxide]]s. Radon can be [[Oxidation|oxidized]] by powerful oxidizing agents such as [[fluorine]], thus forming [[radon difluoride]] ({{chem|RnF|2}}).<ref>{{Unbulleted list citebundle|{{cite journal |author=Stein, L. |date=1970 |journal=[[Science (journal)|Science]] |volume=168 |doi=10.1126/science.168.3929.362 |title=Ionic Radon Solution |pmid=17809133 |issue=3929 |bibcode=1970Sci...168..362S |pages=362–4|s2cid=31959268 }}|{{cite journal |author=Pitzer, Kenneth S. |date=1975 |journal=[[Chemical Communications]] |volume=44 |pages=760–761 |title=Fluorides of radon and element 118 |doi=10.1039/C3975000760b |issue=18  |url=https://escholarship.org/uc/item/8xz4g1ff}}}}</ref> It decomposes back to its elements at a temperature of above {{Convert|523|K||abbr=}}, and is reduced by water to radon gas and hydrogen fluoride: it may also be reduced back to its elements by [[hydrogen]] gas.<ref name="Stein" /> It has a low [[volatility (chemistry)|volatility]] and was thought to be {{chem|RnF|2}}. Because of the short half-life of radon and the radioactivity of its compounds, it has not been possible to study the compound in any detail. Theoretical studies on this molecule predict that it should have a Rn–F [[Bond length|bond distance]] of 2.08&nbsp;[[ångström]]s (Å), and that the compound is thermodynamically more stable and less volatile than its lighter counterpart [[xenon difluoride]] ({{chem|XeF|2}}).<ref>{{cite journal |doi=10.1021/jp9825516 |title=Chemical Bonding in XeF<sub>2</sub>, XeF<sub>4</sub>, KrF<sub>2</sub>, KrF<sub>4</sub>, RnF<sub>2</sub>, XeCl<sub>2</sub>, and XeBr<sub>2</sub>: From the Gas Phase to the Solid State |date=1998 |author=Meng-Sheng Liao |author2=Qian-Er Zhang |journal=[[The Journal of Physical Chemistry A]] |volume=102 |page=10647 |issue=52 |bibcode=1998JPCA..10210647L}}</ref> The [[Octahedral molecular geometry|octahedral molecule]] [[Radon hexafluoride|{{chem|RnF|6}}]] was predicted to have an even lower [[enthalpy of formation]] than the difluoride.<ref>{{cite journal |doi=10.1039/b212460m |title=Bonding in radon hexafluoride: An unusual relativistic problem? |date=2003 |author=Filatov, Michael |journal=[[Physical Chemistry Chemical Physics]] |volume=5 |page=1103 |last2=Cremer |first2=Dieter |issue=6 |bibcode=2003PCCP....5.1103F}}</ref> The [RnF]<sup>+</sup> [[ion]] is believed to form by the following reaction:<ref>{{cite journal |doi=10.1016/S0022-1139(00)85275-6 |title=Noble-gas fluorides |date=1986 |author=Holloway, J. |journal=Journal of Fluorine Chemistry |volume=33 |issue=1–4 |page=149|bibcode=1986JFluC..33..149H }}</ref>

: Rn (g) + 2 {{chem|[O|2|]|+|[SbF|6|]|-}} (s) → {{chem|[RnF]|+|[Sb|2|F|11|]|-}} (s) + 2 {{chem|O|2}} (g)

For this reason, [[antimony pentafluoride]] together with [[chlorine trifluoride]] and {{Chem|N|2|F|2|Sb|2|F|11}} have been considered for radon gas removal in [[Uranium mining|uranium mines]] due to the formation of radon–fluorine compounds.<ref name="Ullmann">{{Ullmann |first1=Cornelius |last1=Keller |first2=Walter |last2=Wolf |first3=Jashovam |last3=Shani |title=Radionuclides, 2. Radioactive Elements and Artificial Radionuclides |doi=10.1002/14356007.o22_o15}}</ref> Radon compounds can be formed by the decay of radium in radium halides, a reaction that has been used to reduce the amount of radon that escapes from targets during [[irradiation]].<ref name="Stein" /> Additionally, salts of the [RnF]<sup>+</sup> cation with the anions {{chem|SbF|6|-}}, {{chem|TaF|6|-}}, and {{chem|BiF|6|-}} are known.<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> Radon is also oxidised by [[dioxygen difluoride]] to {{chem|RnF|2}} at {{Convert|173|K||abbr=}}.<ref name="Stein" />

Radon oxides are among the few other reported [[Radon compounds|compounds of radon]];<ref>{{cite journal |title=The Chemistry of Radon |volume=51 |issue=1 |journal=[[Russian Chemical Reviews]] |date=1982 |page=12 |author=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> only the trioxide ({{Chem|Rn|O|3}}) has been confirmed.<ref name="RnO3" /> The higher fluorides {{chem|RnF|4}} and {{chem|RnF|6}} have been claimed, are calculated to be stable, but have not been confirmed.<ref name="Thayer">{{cite book |last1=Thayer |first1=John S. |title=Relativistic Methods for Chemists |volume=10 |year=2010 |page=80 |doi=10.1007/978-1-4020-9975-5_2|chapter=Relativistic Effects and the Chemistry of the Heavier Main Group Elements |isbn=978-1-4020-9974-8 |series=Challenges and Advances in Computational Chemistry and Physics }}</ref> They may have been observed in experiments where unknown radon-containing products distilled together with [[xenon hexafluoride]]: these may have been {{chem|RnF|4}}, {{chem|RnF|6}}, or both.<ref name="Stein" /> Trace-scale heating of radon with xenon, fluorine, [[bromine pentafluoride]], and either [[sodium fluoride]] or [[nickel fluoride]] was claimed to produce a higher fluoride as well which [[Hydrolysis|hydrolysed]] to form {{chem|RnO|3}}. While it has been suggested that these claims were really due to radon precipitating out as the solid complex [RnF]{{su|p=+|b=2}}[NiF<sub>6</sub>]<sup>2−</sup>, the fact that radon [[Coprecipitation|coprecipitates]] from [[aqueous solution]] with {{Chem|CsXeO|3|F}} has been taken as confirmation that {{chem|RnO|3}} was formed, which has been supported by further studies of the hydrolysed solution. That [RnO<sub>3</sub>F]<sup>−</sup> did not form in other experiments may have been due to the high concentration of fluoride used. [[Electromigration]] studies also suggest the presence of cationic [HRnO<sub>3</sub>]<sup>+</sup> and anionic [HRnO<sub>4</sub>]<sup>−</sup> forms of radon in [[Weak Acid|weakly acidic]] aqueous solution (pH &gt; 5), the procedure having previously been validated by examination of the homologous xenon trioxide.<ref name="RnO3" />

The [[decay technique]] has also been used. Avrorin et al. reported in 1982 that <sup>212</sup>[[francium|Fr]] compounds cocrystallised with their caesium analogues appeared to retain chemically bound radon after electron capture; analogies with xenon suggested the formation of RnO<sub>3</sub>, but this could not be confirmed.<ref>{{cite journal |last1=Avrorin |first1=V. V. |last2=Krasikova |first2=R. N. |last3=Nefedov |first3=V. D. |last4=Toropova |first4=M. A. |date=1982 |title=The Chemistry of Radon |url= |journal=Russian Chemical Reviews |volume=51 |issue=1 |pages=12–20 |doi=10.1070/RC1982v051n01ABEH002787 |bibcode=1982RuCRv..51...12A |s2cid=250906059 |access-date=}}</ref>

It is likely that the difficulty in identifying higher fluorides of radon stems from radon being kinetically hindered from being oxidised beyond the divalent state because of the strong ionicity of [[radon difluoride]] ({{chem|RnF|2}}) and the high positive charge on radon in RnF<sup>+</sup>; spatial separation of {{chem|RnF|2}} molecules may be necessary to clearly identify higher fluorides of radon, of which {{chem|RnF|4}} is expected to be more stable than {{chem|RnF|6}} due to [[Spin–orbit interaction|spin–orbit]] splitting of the 6p shell of radon (Rn<sup>IV</sup> would have a closed-shell 6s{{su|p=2}}6p{{su|b=1/2|p=2}} configuration). Therefore, while {{chem|RnF|4}} should have a similar stability to [[xenon tetrafluoride]] ({{chem|XeF|4}}), {{chem|RnF|6}} would likely be much less stable than [[xenon hexafluoride]] ({{chem|XeF|6}}): [[radon hexafluoride]] would also probably be a [[octahedral molecular geometry|regular octahedral]] molecule, unlike the distorted octahedral structure of {{chem|XeF|6}}, because of the [[inert pair effect]].<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 name="Seppelt">{{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> Because radon is quite electropositive for a noble gas, it is possible that radon fluorides actually take on highly fluorine-bridged structures and are not volatile.<ref name="Seppelt"/> Extrapolation down the noble gas group would suggest also the possible existence of RnO, RnO<sub>2</sub>, and RnOF<sub>4</sub>, as well as the first chemically stable noble gas chlorides RnCl<sub>2</sub> and RnCl<sub>4</sub>, but none of these have yet been found.<ref name="Stein" />

Radon [[carbonyl]] (RnCO) has been predicted to be stable and to have a [[linear molecular geometry]].<ref>{{cite journal |doi=10.1002/qua.963 |title=Prediction of the existence of radon carbonyl: RnCO |date=2002 |author=Malli, Gulzari L. |journal=[[International Journal of Quantum Chemistry]] |volume=90 |page=611 |issue=2}}</ref> The molecules {{chem|Rn|2}} and RnXe were found to be significantly stabilized by [[Angular momentum coupling|spin-orbit coupling]].<ref>{{cite journal |doi=10.1002/(SICI)1097-461X(1998)66:2<131::AID-QUA4>3.0.CO;2-W |title=Relativistic pseudopotential calculations on Xe<sub>2</sub>, RnXe, and Rn<sub>2</sub>: The van der Waals properties of radon |date=1998 |author=Runeberg, Nino |journal=[[International Journal of Quantum Chemistry]] |volume=66 |page=131 |last2=Pyykkö |first2=Pekka |issue=2}}</ref> Radon caged inside a [[fullerene]] has been proposed as a drug for [[tumors]].<ref>{{Unbulleted list citebundle|{{cite news |last=Browne |first=Malcolm W. |url=https://query.nytimes.com/gst/fullpage.html?res=9F0CE2DE1E3CF936A35750C0A965958260&sec=&spon=&pagewanted=all |title=Chemists Find Way to Make An 'Impossible' Compound |work=The New York Times |date=1993-03-05 |access-date=2009-01-30}}|{{Cite journal |last1=Dolg |first1=M. |last2=Küchle |first2=W. |last3=Stoll |first3=H. |last4=Preuss |first4=H. |last5=Schwerdtfeger |first5=P. |date=1991-12-20 |title=Ab initio pseudopotentials for Hg to Rn: II. Molecular calculations on the hydrides of Hg to At and the fluorides of Rn |journal=Molecular Physics |language=en |volume=74 |issue=6 |pages=1265–1285 |doi=10.1080/00268979100102951 |issn=0026-8976 |bibcode=1991MolPh..74.1265D}}}}</ref> Despite the existence of Xe(VIII), no Rn(VIII) compounds have been claimed to exist; {{chem|RnF|8}} should be highly unstable chemically<ref name="Thayer" /> (XeF<sub>8</sub> is thermodynamically unstable).

Radon reacts with the liquid [[interhalogen|halogen fluorides]] ClF, {{chem|ClF|3}}, {{chem|ClF|5}}, {{chem|BrF|3}}, {{chem|BrF|5}}, and {{chem|IF|7}} to form {{chem|RnF|2}}. In halogen fluoride solution, radon is nonvolatile and exists as the RnF<sup>+</sup> and Rn<sup>2+</sup> cations; addition of fluoride anions results in the formation of the complexes {{chem|RnF|3|-}} and {{chem|RnF|4|2-}}, paralleling the chemistry of [[beryllium]](II) and [[aluminium]](III).<ref name="Stein" /> The [[standard electrode potential]] of the Rn<sup>2+</sup>/Rn couple has been estimated as +2.0&nbsp;V,<ref>{{cite journal |title=Standard Electrode Potentials and Temperature Coefficients in Water at 298.15 K |last=Bratsch |first=Steven G. |date=29 July 1988 |journal=Journal of Physical and Chemical Reference Data |volume=18 |issue=1 |pages=1–21 |bibcode=1989JPCRD..18....1B |doi=10.1063/1.555839 |s2cid=97185915 }}</ref> although there is no evidence for the formation of stable radon ions or compounds in aqueous solution.<ref name="Stein" />

=== Isotopes ===
{{Main|Isotopes of radon}}

Radon has no [[stable isotope]]s. Thirty-nine radioactive isotopes have been characterized, with [[mass number]]s ranging from 193 to 231.<ref name="Sonzogni-2011">{{cite web|author=Sonzogni, Alejandro|title=Interactive Chart of Nuclides|url=http://www.nndc.bnl.gov/chart/|access-date=2008-06-06|publisher=Brookhaven National Laboratory|location=National Nuclear Data Center|archive-date=2011-07-21|archive-url=https://web.archive.org/web/20110721051025/http://www.nndc.bnl.gov/chart/|url-status=dead}}</ref><ref name="229Rn">{{cite journal|last1=Neidherr|first1=D.|last2=Audi|first2=G.|last3=Beck|first3=D.|last4=Baum|first4=K.|last5=Böhm|first5=Ch.|last6=Breitenfeldt|first6=M.|last7=Cakirli|first7=R. B.|last8=Casten|first8=R. F.|last9=George|first9=S.|last10=Herfurth|first10=F.|last11=Herlert|first11=A.|date=19 March 2009|title=Discovery of {{sup|229}}Rn and the Structure of the Heaviest Rn and Ra Isotopes from Penning-Trap Mass Measurements|url=https://cds.cern.ch/record/1190495/files/PhysRevLett.102.112501.pdf|journal=[[Physical Review Letters]]|volume=102|issue=11|pages=112501–1–112501–5|bibcode=2009PhRvL.102k2501N|doi=10.1103/PhysRevLett.102.112501|pmid=19392194|last13=Kowalska|first21=L.|first12=A.|last12=Kellerbauer|last22=Stora|first22=T.|last21=Schweikhard|last20=Schwarz|first14=D.|first20=S.|last19=Rosenbusch|first19=M.|last18=Penescu|first18=L.|last17=Noah|first17=E.|last16=Naimi|first16=S.|last15=Minaya-Ramirez|first15=E.|first13=M.|last14=Lunney}}</ref> Six of them, from 217 to 222 inclusive, occur naturally. The most stable isotope is {{sup|222}}Rn (half-life 3.82&nbsp;days), which is a decay product of [[radium-226|{{sup|226}}Ra]], the latter being itself a decay product of [[uranium-238|{{sup|238}}U]].<ref>{{cite web|title=Principal Decay Scheme of the Uranium Series|url=http://www.gulflink.osd.mil/library/randrep/du/mr1018.7.appa.html|url-status=dead|archive-url=https://web.archive.org/web/20081025025424/http://www.gulflink.osd.mil/library/randrep/du/mr1018.7.appa.html|archive-date=2008-10-25|access-date=2008-09-12|publisher=Gulflink.osd.mil}}</ref> A trace amount of the (highly unstable) isotope {{sup|218}}Rn (half-life about 35&nbsp;[[millisecond]]s) is also among the daughters of {{sup|222}}Rn. The isotope {{sup|216}}Rn would be produced by the [[double beta decay]] of natural {{sup|216}}Po; while energetically possible, this process has however never been seen.<ref name="Tretyak2002">{{Cite journal
 |last1=Tretyak |first1=V.I. 
 |last2=Zdesenko |first2=Yu.G. 
 |year=2002
 |title=Tables of Double Beta Decay Data — An Update
 |journal=[[At. Data Nucl. Data Tables]] |volume=80 |issue=1 |pages=83–116
 |doi=10.1006/adnd.2001.0873
|bibcode=2002ADNDT..80...83T }}</ref>

Three other radon isotopes have a half-life of over an hour: {{sup|211}}Rn (about 15&nbsp;hours), {{sup|210}}Rn (2.4&nbsp;hours) and {{sup|224}}Rn (about 1.8&nbsp;hours). However, none of these three occur naturally. {{sup|220}}Rn, also called thoron, is a natural decay product of the most stable thorium isotope ({{sup|232}}Th). It has a half-life of 55.6 seconds and also emits [[alpha radiation]]. Similarly, {{sup|219}}Rn is derived from the most stable isotope of [[actinium]] ({{sup|227}}Ac)—named "actinon"—and is an alpha emitter with a half-life of 3.96 seconds.<ref name="Sonzogni-2011" /> <!-- No radon isotopes occur significantly in the neptunium (237Np) decay series, though trace amounts of the isotopes 221Rn (26 minutes) and 217Rn (0.5 millisecond) are produced in minor branches. -->
[[Image:Decay chain(4n+2, Uranium series).svg|thumb|upright=1.3|alt=Uranium series|The radium or uranium series]]

=== Daughters ===
{{Main|Decay chain#Uranium series}}
{{Sup|222}}Rn belongs to the radium and uranium-238 decay chain, and has a half-life of 3.8235 days. Its first four products (excluding marginal [[decay scheme]]s) are very short-lived, meaning that the corresponding disintegrations are indicative of the initial radon distribution. Its decay goes through the following sequence:<ref name="Sonzogni-2011" />
* {{Sup|222}}Rn, 3.82 days, [[alpha decay]]ing to...
* {{Sup|218}}[[Polonium|Po]], 3.10 minutes, alpha decaying to...
* {{Sup|214}}[[Lead|Pb]], 26.8 minutes, [[beta decay]]ing to...
* {{Sup|214}}[[Bismuth|Bi]], 19.9 minutes, beta decaying to...
* {{Sup|214}}Po, 0.1643&nbsp;ms, alpha decaying to...
* {{Sup|210}}Pb, which has a much longer half-life of 22.3 years, beta decaying to...
* {{Sup|210}}Bi, 5.013 days, beta decaying to...
* {{Sup|210}}Po, 138.376 days, alpha decaying to...
* {{Sup|206}}Pb, stable.

The radon equilibrium factor<ref>{{cite web |access-date=2009-07-07 |url=http://progenygrp.com/why_measure_rdps.htm |title=Why Measure RDPs? |url-status=dead |archive-url=https://web.archive.org/web/20150225020349/http://progenygrp.com/why_measure_rdps.htm |archive-date=2015-02-25}}</ref> is the ratio between the activity of all short-period radon progenies (which are responsible for most of radon's biological effects), and the activity that would be at equilibrium with the radon parent.

If a closed volume is constantly supplied with radon, the concentration of short-lived isotopes will increase until an equilibrium is reached where the overall decay rate of the decay products equals that of the radon itself. The equilibrium factor is 1 when both activities are equal, meaning that the decay products have stayed close to the radon parent long enough for the equilibrium to be reached, within a couple of hours. Under these conditions, each additional pCi/L of radon will increase exposure by 0.01&nbsp;''[[working level]]'' (WL, a measure of radioactivity commonly used in mining). These conditions are not always met; in many homes, the equilibrium factor is typically 40%; that is, there will be 0.004&nbsp;WL of daughters for each pCi/L of radon in the air.<ref name="EPA03" /> {{Sup|210}}Pb takes much longer to come in equilibrium with radon, dependent on environmental factors,<ref>{{Cite journal |last1=Joshi |first1=L. U. |last2=Rangarajan |first2=C. |last3=Sarada Gopalakrishnan |first3=Smt. |date=1969 |title=Measurement of lead-210 in surface air and precipitation |url=https://a.tellusjournals.se/articles/2832/files/submission/proof/2832-1-46460-1-10-20221018.pdf |journal=Tellus |volume=21 |issue=1|page=107 |doi=10.1111/j.2153-3490.1969.tb00423.x |bibcode=1969Tell...21..107J }}</ref> but if the environment permits accumulation of dust over extended periods of time, <sup>210</sup>Pb and its decay products may contribute to overall radiation levels as well. Several studies on the radioactive equilibrium of elements in the environment find it more useful to use the ratio of other {{Sup|222}}Rn decay products with {{Sup|210}}Pb, such as {{Sup|210}}Po, in measuring overall radiation levels.<ref>{{Unbulleted list citebundle|{{Cite journal|url=https://inis.iaea.org/collection/NCLCollectionStore/_Public/53/079/53079681.pdf |title=Radioactive lead in the environment and in the human body |last=Jaworowski |first=Z. |publisher=Institute of Nuclear Research |location=Warsaw, Poland |journal=At. Energy Rev. |date= 1969 |volume=7 |issue=1 }}|{{Cite journal|title=Polonium-210 and Lead-210 in the Terrestrial environment: A historical review |first1=Bertil R.R. |last1=Persson |first2=Elis |last2=Holm |doi=10.1016/j.jenvrad.2011.01.005 |pmid=21377252 |journal= J Environ Radioact |date=May 2011 |volume=102 |issue=5 |pages=420–9|bibcode=2011JEnvR.102..420P }}}}</ref>

Because of their [[electrostatic charge]], radon progenies adhere to surfaces or dust particles, whereas gaseous radon does not. Attachment removes them from the air, usually causing the equilibrium factor in the atmosphere to be less than 1. The equilibrium factor is also lowered by air circulation or air filtration devices, and is increased by airborne dust particles, including cigarette smoke. The equilibrium factor found in epidemiological studies is 0.4.<ref>{{cite book|url=https://books.google.com/books?id=YDRCCNibEqYC&pg=PA179|page=179|title=Health effects of exposure to radon, Volume 6 of BEIR (Series)|publisher=National Academies Press|date=1999|isbn=978-0-309-05645-8}}</ref>