Radon (Rn)
Noble gas · Radioactive
Radon is an invisible, odourless radioactive gas that seeps from uranium-bearing rock into basements. It is the second-leading cause of lung cancer after smoking — and the reason many homes get radon tests.
Position on the periodic table
Atomic properties
| Atomic number | 86 |
|---|---|
| Atomic mass | 222 amu |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 |
| Noble gas shorthand | [Xe] 4f14 5d10 6s2 6p6 |
| Electrons per shell | 2, 8, 18, 32, 18, 8 |
| Valence electrons (outer shell) | 8 |
| Common oxidation states | +2 |
| Electronegativity (Pauling) | 2.2 |
| Covalent radius (approx.) | 150 pm |
| First ionization energy | 1037 kJ/mol |
| Electron affinity | -68 kJ/mol |
Physical properties
| State at 25 °C | Gas |
|---|---|
| Density | 9.73 g/L |
| Melting point | -71.15 °C (202 K) |
| Boiling point | -61.65 °C (211.5 K) |
| Appearance | colorless gas, occasionally glows green or red in discharge tubes |
| Radioactive | Yes |
| Origin | Occurs naturally |
Electron configuration of radon
Radon's ground-state electron configuration is 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6, usually shortened to [Xe] 4f14 5d10 6s2 6p6. Its electrons occupy 6 shells (2, 8, 18, 32, 18, 8), placing it in period 6 of the p-block. The 8 outer-shell electrons drive its bonding behaviour. Explore it interactively in the electron configuration calculator.
Uses of radon
- Historic radiation therapy (radon seeds)
- Earthquake and groundwater research tracer
Biological role: None — a health hazard.
Occurrence: Continuously generated in soil and rock by radium decay; accumulates in enclosed spaces.
History and discovery
Discovered: 1900 — Friedrich Ernst Dorn. Name origin: Named as the “emanation” of radium, later shortened to radon.
Friedrich Ernst Dorn described radium's radioactive emanation around 1900; Ramsay later isolated and weighed it.
Safety notes
Long-term exposure raises lung cancer risk. Testing and ventilation are simple, effective protections.
Educational context only — always follow your school's laboratory rules and never handle chemicals without proper supervision. See our disclaimer.
Practice questions
Quick practice: Radon
1. What is the chemical symbol of Radon?
2. What is the atomic number of Radon?
3. Which category does Radon belong to?
4. What is the state of Radon at room temperature?
5. Which period of the periodic table is Radon in?
Radon FAQs
What is the atomic number of radon?
Radon's atomic number is 86 — every radon atom has 86 protons in its nucleus.
What is the symbol for radon?
Rn. Named as the “emanation” of radium, later shortened to radon.
Is radon a metal, nonmetal, or metalloid?
Radon is classified as a noble gas.
What state is radon at room temperature?
At about 25 °C, radon is a gas. It melts at -71.15 °C.
How many valence electrons does radon have?
Radon has 8 electrons in its outer shell (shell pattern: 2, 8, 18, 32, 18, 8).
What is radon used for?
Key uses include: historic radiation therapy (radon seeds); earthquake and groundwater research tracer.
Related elements
Keep working with this element
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