Radon is a radioactive noble gas produced in natural decay processes, including the decay of radium-226 in rocks. It can move from the ground into surrounding air and accumulate indoors. Radon connects the apparently solid geological world to gas transport and changes in atomic nuclei.
FROM ELEMENT TO APPLICATION
AN ELEMENT IN CONTEXT
Why can a radon signal reveal water exchange without directly measuring flow?
Naturally occurring radon-222 dissolved in water
FOLLOW THIS RELATIONSHIP
Compare water compartments
Groundwater and surface water can carry different radon signals. Their contrast makes the isotope useful as a tracer when studying exchange between connected water bodies.
Explore the model (optional)
RnFORM → INTERACTION → CONSEQUENCE
Follow the explanation in either direction. These are authored steps, not a physical clock.
Optional: check your understanding
USE THE EXPLANATION
Why could two sites with the same radon concentration have different exchange rates?
Atomic identity, reference properties and structure models
INTERACTIVE 3D86 visible sites
An electron censusDrag to rotate · scroll or pinch to zoom
[Xe] 4f14 5d10 6s2 6p6. Grouping electrons by principal shell connects the neutral-atom configuration to periodic-table patterns.
What this representation means
A three-dimensional counting diagram. Dots are count markers, not measured electron positions; spherical placement and spacing are arbitrary. There are no electron trajectories here. Orbitals describe quantum states.
Radon emerged from investigations of mysterious radioactive emanations. Rutherford and Owens observed a gas associated with thorium in 1899, and Friedrich Ernst Dorn studied the emanation from radium in 1900. Later measurements established its place among the noble gases. The apparently different emanations were eventually understood through , showing how one element can appear in several radioactive families without having several chemical identities.
1899
Thorium emanation observed
Rutherford and Owens investigate a radioactive gas from thorium compounds.
1900
Radium emanation studied
Dorn reports the radioactive gas now associated with radon.
Radon is generated in rocks and soils by radioactive , notably of radium. As a gas it can move through pores, enter groundwater and exchange with the atmosphere. Its concentration therefore reflects both the parent material and transport conditions; it is not a permanent atmospheric reservoir like stable noble gases.
Radon has a filled outer shell and behaves as a noble gas under ordinary environmental conditions. Its radioactive decay is a separate nuclear process. A radon atom can move as a gas and later become a different, non-gaseous element, helping explain why transport and decay must be considered together.
Each section links its supporting references. Descriptions and diagrams were authored for this atlas. Source checks completed. Source checks dated 2026-09-06.
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Family labels and the group-3 layout are teaching conventions. A table position does not establish an unknown bulk property. Electronic configurations refer to neutral atoms; ions and material environments require their own account.
Read each reference property together with its units, conditions and the reference information below.
Not yet recorded: electron affinity, second ionization energy, ground-state term symbol, van der waals radius, thermal conductivity, specific heat capacity, electrical resistivity, crystal structure, lattice parameter a, space group, abundance in seawater, abundance in the universe, annual production, supply-risk listing, hazard classification, biological role, cas registry number, pubchem cid, wikidata item. These families are declared and awaiting an ingestion run against the source each names; they are listed here rather than shown as empty rows.
Physical
Intended reference: CRC Handbook of Chemistry and Physics · CRC Press
Phase at 20 °C
gas
293.15 K, 101.325 kPa
Melting point in K
202 K
at standard pressure unless noted
Boiling point in K
211.5 K
101.325 kPa
Density in g/cm³
0.00973 g/cm³
solids and liquids at 293 K; gases at 273 K and 101.325 kPa
Atomic and electronic
Intended reference: Pauling electronegativity scale · Widely tabulated; original in The Nature of the Chemical Bond
Electronegativity
Not recorded
Pauling scale
First ionization energy in kJ/mol
1037 kJ/mol
gas-phase neutral atom, ground state
Covalent radius in pm
150 pm
single-bond covalent radius
Common oxidation states
0, +2
states met in ordinary compounds; not exhaustive
Occurrence and identity
Intended reference: CRC Handbook of Chemistry and Physics · CRC Press
Abundance in the crust
Not recorded
upper continental crust, mass fraction
Has stable isotopes
Noderived
Discovery year in CE
1900 CEderived
WHERE IT SITS AMONG ITS NEIGHBORS
Electronegativity across period 6
Cs 0.79 Pauling · Cesium
Electronegativity across period 6. Exact values.
Cs
0.79
Ba
0.89
La
1.1
Ce
1.12
Pr
1.13
Nd
1.14
Sm
1.17
Eu
1.2
Gd
1.2
Tb
1.1
Dy
1.22
Ho
1.23
Er
1.24
Tm
1.25
Yb
1.1
Lu
1.27
Hf
1.3
Ta
1.5
W
2.36
Re
1.9
Os
2.2
Ir
2.2
Pt
2.28
Au
2.54
Hg
2
Tl
1.62
Pb
2.33
Bi
2.02
Po
2
At
2.2
Electronegativity down group 18
Kr 3 Pauling · Krypton
Electronegativity down group 18. Exact values.
Kr
3
Xe
2.6
The trend uses the same reference-property values as the periodic table. Elements with no recorded value are left out of the line rather than drawn at zero.
