Radon
[Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁶ · 2 · 8 · 18 · 32 · 18 · 8
A radioactive noble gas that seeps out of the ground into basements. Radon is the second leading cause of lung cancer after smoking, and the first among non-smokers.
3D model
Bohr model: nucleus and electron shells from the real configuration. Valence electrons are highlighted.
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Atomic properties
- Atomic number
- 86
- Atomic mass
- 222 а.е.м. ≈
- Electron configuration
- [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁶
- Electrons per shell
- 2 · 8 · 18 · 32 · 18 · 8
- Block
- p-block
- Group
- Noble gases
- Period
- 6
- Electronegativity (Pauling)
- 2.2
- Electronegativity (Allen)
- 2.6
- Atomic radius
- 120 pm
- Covalent radius
- 150 pm
- Van der Waals radius
- 220 pm
- Ionisation energy 1
- 1 037 kJ/mol
- Electron affinity
- 0 kJ/mol
- Common oxidation states
- 0
- Oxidation states
- 0, +2, +6
Physical properties
- State at 25 °C
- gas
- Density
- 0.00973 g/cm³
- Melting point
- 202 K · -71.2 °C
- Boiling point
- 211.5 K · -61.7 °C
- Speed of sound
- no data
Thermal properties
- Heat of fusion
- 3.247 kJ/mol
- Heat of vaporisation
- 18.1 kJ/mol
- Specific heat capacity
- 0.094 J/(g·K)
- Thermal conductivity
- 0.00361 W/(m·K)
Mechanical properties
- Young's modulus
- no data
- Shear modulus
- no data
- Bulk modulus
- no data
- Poisson ratio
- no data
- Mohs hardness
- no data
- Brinell hardness
- no data
Electrical and magnetic properties
- Electrical resistivity
- no data
- Magnetic ordering
- non-magnetic
- Curie point
- no data
- Néel point
- no data
- Superconducting point
- no data
Crystal structure
- Crystal structure
- face-centred cubic (fcc)
- Lattice constants
- no data
Abundance
- In the crust
- 4·10⁻¹³ mg/kg
- In the ocean
- 0 mg/L
- In the universe
- 0 mg/kg
- In the human body
- 0 mg/kg
Isotopes
| Isotope | Abundance | Half-life | Decay mode |
|---|---|---|---|
| 219Rn | — | 3.96 s | α |
| 220Rn | — | 55.6 s | α |
| 222Rn | — | 3.82 d | α |
Radon-222, half-life 3.8 days, is the daughter of radium-226 and the main source of public radiation dose. Radon-220, thoron, is shorter-lived and travels less far.
Discovery
- Year of discovery
- 1900
- Discovered by
- Friedrich Ernst Dorn
- Where
- Germany
- Origin of the name
- from radium, whose decay produces it
History
Friedrich Dorn noticed in 1900 that radium gives off a radioactive gas, which he called an emanation. Ramsay and Gray isolated it in 1910 and established it as the heaviest noble gas.
Where it occurs
Formed continuously by radium decay in rock. Air concentration depends on geology: granite and shale districts give noticeably more.
How it is produced
From radium sources. There is no practical production.
Role in living things
No biological role. Radon itself does not lodge in the lungs, but its solid decay products settle in the bronchi and irradiate the tissue with alpha particles.
Safety
The WHO attributes 3 to 14 % of all lung cancers to radon. The remedy is sub-floor ventilation and sealing foundations; many countries require a radon measurement when a house is sold.
Uses
- Historically brachytherapy in sealed needles, now displaced by other isotopes
- A geological tracer: radon flux maps faults and has been trialled for eruption forecasting
- A tracer for studying air mass transport
Curiosities
- Radon accounts for roughly half of the natural radiation dose an average person receives.
- Radon is 7.5 times denser than air and pools in cellars and basements.
- In the early twentieth century radon inhalations and radioactive water were sold as health treatments.
- Radon is the one radioactive element most people encounter every single day.