Radon (Rn)
“The noble gas that kills quietly — seeping from soil into bedrooms, it stands second only to smoking as a cause of lung cancer.”
How its electrons are arranged
Computed from the aufbau principle, with known real-world exceptions applied automatically.
Characteristics
- Electron configuration [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁶ — a perfect octet, period 6, group 18, p-block; chemically almost totally inert, which is why “[Rn]” serves as the shorthand core in the configuration of every heavier element.
- Nature’s only radioactive noble gas: radon-222, half-life 3.8 days, wafts up from any soil containing uranium or thorium — meaning, essentially, from all soil.
- Its danger is radioactivity, not chemistry: inhaled radon and its solid decay products (polonium-218, lead-214) lodge in the lungs and fire alpha particles into tissue, making radon the second-leading cause of lung cancer after smoking.
- It is tasteless, odourless and invisible, so only alpha-track detectors or activated-charcoal test kits can reveal a dangerous indoor level; ventilation and sealed floors are the main cures.
A colourless, odourless, tasteless gas at room temperature — about eight times denser than air, making it the heaviest of the natural noble gases. Chilled towards its freezing point of −71 °C, trapped radon phosphoresces a soft orange-red, a spectacle only specialists ever witness.
Where you meet it
✦ Uses
- Historic radiotherapy: “radon seeds” — tiny gold tubes filled with radon gas — were implanted beside tumours in the early 1900s, the ancestor of modern brachytherapy before safer sources replaced them.
- Earthquake research: shifts in underground rock strain before earthquakes can send radon anomalies up through wells and soil gas, so radon monitoring is a studied early-warning method worldwide.
- Groundwater tracing: because radon dissolves in water and decays on a 3.8-day clock, hydrologists use it to map how springs and aquifers mix — a real reason well water is tested in groundwater-dependent countries like Bangladesh.
- Uranium prospecting: surveyors track soil-gas radon with buried detectors to locate hidden uranium ore bodies.
◍ Everyday examples
- Ground-floor rooms and basements in granite-rich districts can accumulate radon — the reason many countries recommend a cheap detector in every basement bedroom.
- Deep tube-well water can carry dissolved radon that escapes into kitchen air when the water is pumped and boiled — part of why hydrologists test groundwater in Bangladesh.
- Every granite countertop and concrete building sits on ground that breathes radon; ordinary levels are trivial, but badly ventilated modern rooms can trap it.
History & name
In 1899 Ernest Rutherford and Robert Owens, working in Montreal, noticed that thorium steadily breathed out a radioactive something they called “emanation”. In 1900 Friedrich Ernst Dorn found the same breath rising over radium in his Halle laboratory and called it radium emanation. William Ramsay later trapped the gas, read its spectrum and confirmed a genuinely new element — briefly christened niton, “the shining one”, before the world settled on radon in 1923. It remains the only noble gas discovered by its radioactivity rather than by any chemical behaviour.