Category: Noble gas
Atomic Number: 86
Period: 6 | Group: 18
Block: p-block
A radioactive noble gas that seeps out of granite and is the second leading cause of lung cancer.
| Property | Value |
|---|---|
| Phase at STP | Gas |
| Density | 0.00970000 g/cm³ |
| Melting Point | 202.00 K (-71.15 °C) |
| Boiling Point | 211.30 K (-61.85 °C) |
| Heat Capacity | N/A |
| Property | Value |
|---|---|
| Atomic Mass | 222.0000 u |
| Electronegativity (Pauling) | 2.20 |
| Oxidation States | 0, +2, +6 |
| Electron Configuration | [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁶ |
| Discovered By | Unknown |
|---|---|
| Discovery Year | 1900 |
| Named After | From radium, its parent element |
Friedrich Ernst Dorn (1900)
Radon was discovered in 1900 by German physicist Friedrich Ernst Dorn at the University of Halle, while studying the radioactive decay of radium. Dorn observed that radium samples continuously produced a radioactive gas that he initially called "radium emanation." This discovery was part of the early radiation research that followed Henri Becquerels discovery of radioactivity in 1896 and Marie and Pierre Curies work with radium.
Early Characterization
Following Dorns initial discovery, scientists William Ramsay and Robert Whytlaw-Gray isolated radon in 1910 and determined its atomic weight, confirming it as a noble gas. They measured its density and found it to be the heaviest known gas at the time. The element was initially called "niton" (from Latin "nitens," meaning shining) due to its luminescent properties, but was renamed "radon" in 1923.
Commercial Exploitation Era
In the early 1900s, radon was considered valuable for its supposed therapeutic properties. Entrepreneurs established "radon spas" and marketed radon-infused water as health tonics. The discovery that radon could make materials luminescent led to its use in self-luminous paint for watch dials and instrument panels, an application that continued until the health risks became apparent in the 1960s.
Health Hazard Recognition
The understanding of radons danger evolved slowly. Lung cancer rates among uranium miners were noted as early as the 1500s, but the connection to radon wasnt established until the 1950s. Comprehensive studies of radon health effects began in the 1970s, leading to the recognition of radon as a major public health threat and the development of modern testing and mitigation programs in the 1980s.
| ISOTOPE | Neutrons | Natural Abundance | Half-life | Decay Mode |
|---|---|---|---|---|
| Rn-209 | 123 | - | 28.8 min | ε/β⁺ (83%), α (17%) |
| Rn-210 | 124 | - | 2.4 hr | α (96%), ε/β⁺ (4%) |
| Rn-211 | 125 | - | 14.6 hr | ε (72.6%), α (27.4%) |
| Rn-220 | 134 | - | 55.6 sec | α |
| Rn-222 | 136 | - | 3.8235 days | α |
| Rn-224 | 138 | - | 107 min | β⁻ |
Data: IAEA Nuclear Data Section, LiveChart of Nuclides, ground-state evaluations, retrieved October 10, 2026. Abundance is the share of atoms in the natural element; a dash means the isotope has no standard natural abundance.
Medical Applications (Historical)
Radon has been used in "radon therapy" since the early 1900s (radon baths began at Jáchymov in 1906, and spas such as Bad Gastein still offer it), in which patients were exposed to radon gas or radioactive water containing radon for treating arthritis, hypertension, and other ailments. These treatments, now known to be extremely dangerous, were based on the misguided belief that small amounts of radiation were beneficial. Today, radon-222 is still occasionally used in very controlled medical research to study lung cancer mechanisms and test radiation protection methods.
Scientific Research Tools
Radon serves as a valuable tracer in atmospheric and geological research. Scientists use radon concentrations to study air mass movements, track pollution dispersion, and understand groundwater flow patterns. Radon-222 acts as a natural "fingerprint" for identifying air masses and studying atmospheric mixing processes. Its decay products help researchers understand particle physics and test radiation detection equipment.
Indoor Air Quality Indicator
Radon measurement has become a crucial tool in public health and real estate. Professional radon testing services use specialized detectors to measure radon concentrations in homes, schools, and workplaces. This application has created an entire industry focused on radon detection, mitigation, and prevention, protecting millions of people from this invisible health hazard.
Educational and Training
Controlled radon sources are used to train radiation safety professionals, health physicists, and environmental scientists. These applications help develop and test radon detection equipment, calibrate monitoring instruments, and research new mitigation techniques. Radon also serves as a model system for studying the behavior of other radioactive gases in the environment.
Decay of uranium and radium
| Earth's Crust | 0.0000000000 ppm |
|---|---|
| Universe | 0.0000000000 % |