What Is Radon?

Radon is a chemical element with the symbol Rn and atomic number 86, classified as a noble gas in Group 18.

A radioactive noble gas. The second leading cause of lung cancer after smoking.

As a noble gas in Period 6 and Group 18 (Noble Gases), radon's placement on the table reflects its electron configuration of [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁶, which governs its bonding behavior and the type of compounds it typically forms.

Position on the Periodic Table

Radon is located in Period 6, an unusually long row that includes the entire lanthanide series.

Within that row, radon sits in Group 18 (Noble Gases), alongside elements that share a similar number of valence electrons and, by extension, similar chemical behavior.

This position is not arbitrary — the periodic table was deliberately organized so that an element's row and column reveal its expected reactivity, bonding pattern, and physical state at a glance.

Physical & Chemical Properties

Radon has an atomic mass of (222) u and a density of 0.00906 g/cm³. Its melting point is -71°C and its boiling point is -61.7°C.

Radon's outer electron shell is completely filled, leaving it with almost no tendency to bond with other elements under ordinary conditions.

Electron Configuration Explained

Radon's electron configuration is [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁶, describing how its electrons are distributed across shells and subshells around the nucleus.

Reading the configuration in order shows electrons filling shells of increasing energy, following the standard Aufbau principle that explains how atomic structure builds up across the periodic table.

The outermost (valence) electrons shown in this configuration are what ultimately determine radon's chemical reactivity and the type of bonds it forms with other elements.

History & Discovery

Radon was formally discovered in 1900, F.E. Dorn, identified through the careful isolation and analytical techniques typical of that era's chemical research.

Many elements from this period were anticipated by Dmitri Mendeleev's periodic table, which successfully predicted gaps corresponding to undiscovered elements well before laboratory instruments existed to confirm them directly.

What Is Radon Used For?

Radon's specific properties make it useful in several applications, including:

  • Cancer treatment (historic)
  • Earthquake detection
  • Leak detection
  • Research
  • Lung cancer risk monitoring

These uses reflect radon's underlying classification as a noble gas, since the same properties that define its category in chemistry also determine where it becomes practically useful.

Fun Facts About Radon

  • Radon is the second leading cause of lung cancer in the US — it seeps up from soil into homes.
  • Radon is element number 86 on the periodic table, in Period 6 and Group 18.
  • Its standard atomic mass is (222) u, calculated from the natural abundance of its isotopes.

Frequently Asked Questions

What is Radon's atomic number?
Radon has atomic number 86.

What is Radon's chemical symbol?
Radon's symbol is Rn.

What group and period is Radon in?
Radon is in Period 6, Group 18 (Noble Gases).

What is Radon's atomic mass?
Radon's standard atomic mass is (222) u.