Radon (Rn)
Radon (Rn) is a colorless, odorless, and tasteless radioactive gas with the atomic number 86, classified as the heaviest naturally occurring member of the noble gases. It forms during the radioactive decay of uranium found in soil, rock, and water, and can accumulate in homes, particularly in basements. Despite its inert chemical nature, radon is associated with serious health risks, including lung cancer, when inhaled over long periods. The gas has a short half-life and produces radioactive decay products such as polonium, which can harm lung tissue. Interestingly, radon levels fluctuate based on environmental conditions and can potentially serve as a predictor for earthquakes, as higher concentrations may precede seismic activity. While radon therapy has been utilized for certain medical conditions, its use is controversial and generally discouraged due to health risks. Methods for controlling radon levels in homes, such as radon mitigation systems, can effectively reduce exposure and minimize health hazards.
Radon (Rn)
- Element Symbol: Rn
- Atomic Number: 86
- Atomic Mass: 222
- Group # in Periodic Table: 18
- Group Name: Noble gases
- Period in Periodic Table: 6
- Block of Periodic Table: p-block
- Discovered by: Friedrich Ernst Dorn (1900)
Radon, with an atomic number of 86 and symbol Rn, was the fifth radioactive element to be discovered, and it is the heaviest naturally occurring radioactive member of the noble gases. The noble gases, which belong to Group 18 in the periodic table, include helium, neon, argon, krypton, xenon, radon, and ununoctium. Radon is a colorless, odorless, tasteless, and chemically inert gas. After the uranium present in rock, soil, and water undergoes radioactive decay, the radon that is formed then travels through the soil to the air above. Studies have shown that radon can cause lung cancer.
In 1899, a radioactive gas released by thorium was detected by Ernest Rutherford and Robert Owens. In the same year, Marie Curie also happened to find a radioactive gas emanating from radium. Then while studying radium’s decay chain in 1900, the German chemist Friedrich Ernst Dorn discovered radon. It is this decay chain that continues to yield the radon that is obtained today. Radon was initially known as niton, which comes from the Latin word nitens, meaning "shining." In 1923, the International Union of Pure and Applied Chemistry (IUPAC) renamed the element, and it has been known as radon ever since
Although radon levels can be used to predict earthquakes, scientists and government agencies have become concerned over time about radon’s effects on the environment. Because radon is a naturally occurring gas whose levels can rise and fall both on a daily basis and also by the hour, it cannot be completely eliminated from the environment. On the other hand, it can be controlled once detected by specialists who have tested for its presence in specific locations. Many methods, for example, have been shown to be effective in lowering radon levels when they become dangerously high, but the most effective method is radon mitigation subslab suction.
Physical Properties
The boiling point of radon is –61.85°C. Below its boiling point, the element dissolves in water to form a clear, colorless liquid. Below –71.15°C, the element’s melting point, radon freezes into a solid that is initially yellow in color. As the temperature is lowered further, its color changes to orange-red. Radon is a gas at 298 K. The standard state of an element is defined as its state at this temperature. The density of radon at the standard temperature and atmosphere (STP) is 9.73 grams per liter. It is roughly nine times denser than air.
Chemical Properties
Radon has a face-centered, cubic structure. Like neon, argon, krypton, and xenon, radon is electronically stable. These elements all fall into the class of elements known as inert gases since their electron configurations have little or no chemical activity. Along with the other stable inert gases, radon has high ionization energies. The oxidation state for radon is 0. Radon is the densest gas, and it exists as a brilliant yellow phosphorescence right below its freezing point. It has a short half-life, is chemically unreactive, and highly radioactive. Radon forms both a difluoride, RnF2, and also derivatives of the difluoride. Many studies have so far detected the presence of ionic radon in many of these solutions, including Rn2+, RnF+, and RnF3. Because of its location in the periodic table, radon is a metalloid element, and thus, radon behaves chemically like a metal fluoride.
Natural radon has isotopes belonging to the radioactive series of elements that include uranium, thorium, and actinium. Originally, radon was known as radium emanation. It belongs to Group 18 in the periodic table. Radon-22 is the most stable radon isotope, with a half-life of 3.823 days. When radon decays, it produces polonium, bismuth, and lead isotopes, which mix with underground water and dust particles.
Radon atoms have an especially stable electron shell configuration. The outer shell of radon has eight electrons, and thus it tends to be chemically inactive. Nevertheless, it is not chemically inert, as demonstrated by the occurrence of radon difluoride, RnF2. Furthermore, radon difluoride is evidently more stable chemically than the compounds of other reactive noble gases.
When a mixture of minute amounts of radon-222 and fluorine gas are heated to roughly 400℃, a nonvolatile radon fluoride is obtained. Also, the oxidation of radon by halogen fluorides, such as ClF3, BrF3, BrF5, IF7, and [NiF6]2−, in HF solutions gives stable solutions of radon fluoride.
Applications
In soil and rock, trace particles of uranium are naturally present. In Earth’s crust, for example, there are estimated to be no more than 4 × 10–13 milligrams per kilogram of radon. Radon forms as the uranium present in the soil particles breaks down. Through cracks in the walls and plumbing, radon thus formed can easily find its way into homes. The radon will generally be found at a higher level in the basement.
Radon is a health hazard when inhaled by humans after it decomposes into polonium. The human body cannot absorb radon directly unless the element first undergoes chemical reactions or forms certain compounds. The chances of getting lung cancer due to exposure to radon are comparable to dying in an accident in your home.
Although long-term exposure to high levels of radon can cause lung cancer, in measured doses, it has been used in radon therapy to treat different illnesses. However, this practice is somewhat controversial in the United States, and a majority of medical practitioners opposes radon’s use for this purpose. There are several radon spas, both in Europe and the United States, that offer radon-based treatment. According to medical experts and the Environmental Protection Agency (EPA), exposure to radon is not without risk. The radionuclides that are produced as a result of the decay of radon affect the lung tissue, posing a risk of cancer. In the past, radon was used in radiation therapy to treat cancer. Today, oncologists prefer to use safer treatments instead.
Scientists believe that rising levels of radon signal the threat of an imminent earthquake. That is, the release of radon gas from below the surface of the earth is one of the many geophysical and geochemical phenomena that suggest that an earthquake is about to happen. According to current theory, radon is present in rock, but before an earthquake, radon gas is released in greater quantities than usual. As radon moves up toward the surface in earthquake-prone areas, its presence can be detected by sensitive strips of film that have been buried in the soil. Such measurements have already been successful in predicting a few earthquakes in the United States, China, and the Soviet Union.
This release of radon generally starts weeks before an earthquake. Nevertheless, because the relationship between rising radon levels and earthquakes is not yet fully understood, systematic radon monitoring networks need to be installed and used in a more widespread way in order to develop a foolproof earthquake-prediction system.
Bibliography
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