Radon element

Written out in full, with the configuration PubChem gives for each noble gas before it (xenon [Kr]5s² 4d¹⁰ 5p⁶, krypton [Ar]4s² 3d¹⁰ 4p⁶, argon [Ne]3s² 3p⁶, neon [He]2s² 2p⁶ and helium 1s²), radon's electrons fall into six shells: 2, 8, 18, 32, 18 and 8. A Bohr model draws exactly that, the nucleus in the middle and each shell as a ring.

A Lewis dot structure shows only the outer shell. Radon's ends in 6s² 6p⁶, a full shell of eight, so its Lewis structure is the symbol Rn with eight dots in four pairs.

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8 valence electrons, drawn as four pairs. They are radon's outer shell, 6s² 6p⁶: 2 + 6, a full shell of eight.

Other radon isotopes have the same 86 protons and different neutron counts; LANL says thirty-nine isotopes are known, and radon-222 is the most common, which is why it is the one the counts above use.

Short answers for each: how many protons and electrons does radon have, how many neutrons does radon have and how many valence electrons does radon have.

One other isotope has a name outside the laboratory. PubChem's record says both radon-220 and radon-222, with half-lives of 56 seconds and 3.8 days respectively, are used to study underground environmental and atmospheric gaseous-transport processes.

EPA's Radioactive Decay page defines half-life as the time required for half of the radioactive atoms present to decay. For radon-222 that means half of any given amount has turned into something else in under four days. Some radionuclides, EPA notes, have half-lives of mere seconds and others of millions or billions of years.

A short half-life does not mean radon runs out. LANL estimates that every square mile of soil to a depth of 6 inches contains about 1 gram of radium, which releases radon in tiny amounts into the atmosphere.

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1. 238U

   Uranium-238

   Solid

2. 234U

   Uranium-234

   Solid

3. 230Th

   Thorium-230

   Solid

4. 226Ra

   Radium-226

   Solid

   Half-life 1600 years

5. 222Rn

   Radon-222

   Gas

   Half-life 3.823 days

6. ···

   Radon's decay products

7. 206Pb

   Lead-206

   Solid

• Uranium-238. More than 99 percent of the uranium found in the environment is in the form of U-238. Uranium decays by alpha particles.
• Uranium-234. Less than one percent of natural uranium, but much more radioactive.
• Thorium-230. An intermediate EPA names in the uranium-238 chain.
• Radium-226. Radium decays to produce radon gas.
• Radon-222. The most common radon isotope, and an alpha emitter. As a gas it can move up through the ground and into a building.
• Radon's decay products. Radon gas decays into radioactive particles that can get trapped in your lungs when you breathe.
• Lead-206. Where the chain ends. Only the final, stable atom in the chain is not radioactive.

EPA names uranium-234, thorium-230, radium-226 and radon-222 as intermediates "such as" these, so the chain has more steps than are drawn. Half-lives are shown only where a cited source states one.

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EPA adds that the decay products within a chain are always radioactive, and only the final, stable atom is not. That is why radon's story does not end when a radon atom decays. ATSDR describes the scale of the process: each atom of uranium or thorium decays or transforms about a dozen times, each time expelling radiation and forming a different element with different radioactive properties, and radium and then radon are formed midway through these decay chains.

• 1898: Radium is discovered by Madame Curie in the pitchblende, according to LANL's radium text.
• 1900: Dorn discovers the element and calls it radium emanation, according to LANL.
• 1908: Ramsay and Gray isolate the element, name it niton and determine its density, finding it to be the heaviest known gas. LANL notes niton comes from the Latin nitens, meaning shining.
• 1923: The element has been called radon since this year, a name derived from radium.

LANL's radium text also records how radon was handled in those decades: one gram of radium produces about 0.0001 milliliter of emanation, or radon gas, per day, which was purged from the radium and sealed in minute tubes. More on when radon was discovered.

That use goes back to the early radium era. LANL's radium text says the radon purged from radium was sealed in minute tubes used in the treatment of cancer and other diseases. EPA's radium page adds that radium was historically used in medical treatments and devices.

Because radon is a noble gas, ATSDR says, it releases from any chemical bonds that attach it, and it may travel far enough to reach groundwater or the air. Radon progeny, the radioactive atoms with short half-lives into which radon quickly decays, are what make the element matter for health.

Radon is heavier than air, but that does not confine it to the basement. WHO says levels are usually higher in basements, cellars and living spaces in contact with the ground, and that considerable radon concentration can also be found above the ground floor. See is radon heavier than air.

The harm comes from decay. LANL says the main hazard is inhalation of the element and its solid daughters, which are collected on dust in the air. EPA's Radiation Basics page explains that alpha particles cannot get through skin but can damage sensitive living tissue if alpha emitters are inhaled, swallowed or get into the body through a cut.

PubChem's summary explains why an alpha emitter that is easy to block is still a concern. Alpha decay usually isn't considered to be a great radiological hazard since the alpha particles produced by the decay are easily stopped. However, since radon is a gas, it is easily inhaled and living tissue is directly exposed to the radiation, and radon decays into longer lived, solid, radioactive elements which can collect on dust particles and be inhaled as well.

EPA's Radionuclide Basics page says exposure to radon is the second leading cause of lung cancer after smoking, and that for most people radon is the single greatest environmental source of radiation exposure. The radon and lung cancer guide covers that risk in full.

EPA recommends fixing a home when the radon level is 4 pCi/L or higher. To see the predicted radon potential where you live, open the radon map or your state radon report. Then follow the radon testing guide, read your number with the result interpreter, and if it is high, see how radon mitigation works or find a certified provider in the radon professionals directory.