Radon (Rn) — Properties, Uses & Safety

Overview

Radon (Rn) is a naturally occurring radioactive noble gas with an atomic mass of approximately 222 g/mol (for its most stable isotope, radon-222). It is colorless, odorless, and tasteless, making it undetectable by human senses — a particularly dangerous characteristic given its health risks. Radon is produced by the radioactive decay of radium-226, which itself is part of the uranium-238 decay chain. As uranium is present in trace amounts in most rocks and soils, radon gas seeps continuously from the ground and can accumulate in enclosed spaces, particularly basements and ground-floor rooms of buildings. Radon is the second leading cause of lung cancer after smoking, responsible for an estimated 21,000 deaths per year in the United States alone. The GHS hazard code H280 (gas under pressure) applies to compressed radon, and radiation hazard symbols are required. As a noble gas, radon has a complete outer electron shell and is chemically inert under normal conditions, though a few radon compounds (such as radon difluoride, RnF2) have been synthesized under extreme conditions. Radon's radioactivity means it undergoes alpha decay (Rn-222 -> Po-218 + He-4) with a half-life of 3.82 days. The short-lived decay products (polonium-218 and polonium-214) are solid particles that can lodge in lung tissue and continue emitting alpha radiation, causing cellular damage. Testing homes for radon is recommended by health agencies worldwide, and mitigation systems using sub-slab depressurization can reduce indoor radon levels by up to 99%. For chemistry students, radon connects to nuclear chemistry (alpha decay, half-life calculations, decay chains), noble gas properties and electron configuration, the concept of radioactive equilibrium, and the real-world application of chemistry to public health. Calculating radon decay rates provides practical exercises in first-order kinetics and half-life problems.

IUPAC Name

radon

CAS Number

10043-92-2

PubChem CID

24857

Molecular Formula

Rn

Molar Mass

222 g/mol

State at STP

gas

Appearance

Colorless, odorless radioactive gas