Radon

A radioactive noble gas that seeps out of the ground into basements, and a leading cause of lung cancer.

At a glance

Symbol: Rn
Atomic number: 86
Mass number of its longest-lived isotope: [222]
Group: 18
Period: 6
Family: noble gas
Electron configuration: [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁶
Valence electrons: 8
Electronegativity: not measured
Isotopes: none are stable; ²²²Rn, with a half-life of 3.8 days, is the one found in homes

On the table

Period 6, group 18. The other noble gases are tinted, and every cell opens its own article.

Electrons and bonding

A full valence shell, like the other noble gases, but its outer electrons are held loosely enough that it can form a fluoride. Its radioactivity makes that chemistry hard to study.

Properties

State at 25 °C: gas
What it looks like: colorless, odorless, radioactive gas
Melting point: −71 °C
Boiling point: −61.7 °C
Density: 9.73 g/L at 0 °C and 1 atm

Where it is found

Made continuously in soil and rock as uranium and radium decay. It seeps into buildings, especially basements, and is the largest source of natural radiation for most people.

Discovery and name

Ernest Rutherford and Robert Owens noticed a radioactive gas given off by thorium in 1899, and Friedrich Ernst Dorn found the one given off by radium in 1900. William Ramsay and Robert Whytlaw-Gray isolated it in 1908 and called it niton, from the Latin for shining. The name radon, after radium, was adopted in 1923.

What it is used for

Once used in cancer radiotherapy; today it is measured far more than it is used. Radon levels help scientists trace the movement of air and groundwater and study earthquakes.

In compounds

RnF₂radon difluoride

Handle with care

Breathing radon for years raises the risk of lung cancer, especially for smokers; in the United States it is the second leading cause of lung cancer after smoking. Home test kits are cheap, and ventilating basements lowers the level.