Radon (Rn)

Radon is the second leading cause of lung cancer after smoking, and the exposure happens at home: uranium in the ground decays to radium and then to radon, an inert gas that seeps up through foundations and accumulates in basements. Because it is chemically inert it is breathed in and out freely, but its decay products are solid and stick to lung tissue. Testing a house costs very little and remediation is usually a fan and a pipe, which makes it one of the more tractable environmental health risks there is.

Properties

Atomic number

86

Symbol

Rn

Mass number of most stable isotope

[222]

Category

Noble gas

Group

18

Period

6

Block

p-block

Electron configuration

[Xe] 6s² 4f¹⁴ 5d¹⁰ 6p⁶

Electrons per shell

2, 8, 18, 32, 18, 8

Melting point

202 K — -71.1 °C — -96.1 °F

Boiling point

211.45 K — -61.7 °C — -79.1 °F

Density

0.00973 g/cm³

Oxidation states

0

Discovered

1900 by Friedrich Ernst Dorn

Electron configuration

Full

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶

Noble gas shorthand

[Xe] 6s² 4f¹⁴ 5d¹⁰ 6p⁶

Shells

K: 2 · L: 8 · M: 18 · N: 32 · O: 18 · P: 8

What it is used for

• Historically sealed in needles for cancer radiotherapy
• A tracer for studying air movement and for earthquake prediction research

Hazards

• The leading cause of lung cancer in non-smokers
• Colourless, odourless and eight times denser than air, so it collects in basements
• Risk depends entirely on local geology; neighbouring houses can differ

No stable isotope; the mass given is the mass number of radon-222, the longest-lived at 3.82 days. Density is the gas at 0 °C and 101.325 kPa, which makes radon the densest gas at room conditions.

Neighbours in the table

Group 18

Elements in the same group share their outer electron count, which is why they behave similarly in reactions. Radon sits in group 18 with helium, neon, argon, krypton, xenon, oganesson.