Radon element

Radon symbol and atomic number

The radon symbol is Rn and its atomic number is 86, and PubChem's table puts it in the noble gas group block with helium, neon, argon, krypton and xenon. LANL notes the name was derived from radium; it was called niton at first, from the Latin word nitens meaning shining. PubChem gives radon an atomic mass of 222.01758, against 131.29 for xenon and 83.80 for krypton.

What group is radon in?

Radon is a noble gas. LANL's page says it occupies the last place in the zero group of gases in the periodic table, the older name for the column of noble gases, and ATSDR calls radon a naturally occurring, radioactive, noble gas. PubChem's group block for radon is simply "Noble gas". The short answer is on what group is radon in.

Radon atomic mass

PubChem gives radon an atomic mass of 222.01758. That tracks radon-222, the isotope LANL names as the most common. See what is the atomic mass of radon for how the two figures relate.

Radon electron configuration

PubChem gives the radon electron configuration as [Xe] 6s2 4f14 5d10 6p6. The [Xe] stands for the electrons of a xenon atom, and the rest is written out. That notation is the key to several of the questions people ask about radon, from how many electrons it has to why it rarely forms compounds.

The counts people search for most can be worked out from the figures above. An element's atomic number is the number of protons in the nucleus, so every radon atom has 86 protons. EPA defines isotopes as forms of an element with the same number of protons but a different number of neutrons, which is why the neutron count depends on the isotope.

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.

LANL reports that thirty-nine isotopes of radon are known and that radon-222 is the most common. It has a half-life of 3.823 days and is an alpha emitter. EPA's Radionuclide Basics page gives the same figures in rounder form: alpha particles, and a half-life of 3.8 days.

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.

Radon is a middle step in a long series of transformations. EPA explains that when a radionuclide decays, it transforms into a different atom, a decay product, and that the atoms keep transforming until they reach a stable state. The series is called a decay chain, and EPA gives the uranium-238 chain as its example: it culminates in lead-206 after forming intermediates such as uranium-234, thorium-230, radium-226 and radon-222.

1. 1

   Uranium-238

   EPA says more than 99 percent of the uranium found in the environment is uranium-238, and that uranium is present naturally in virtually all soil, rock and water.

2. 2

   Uranium-234 and thorium-230

   Intermediates EPA names in the same chain on the way to radium.

3. 3

   Radium-226

   LANL gives radium-226, the common isotope of radium, a half-life of 1,600 years, and PubChem's radium record says it decays into radon-222 through alpha decay. EPA's radium page says radium decays to produce radon gas.

4. 4

   Radon-222

   A gas with a 3.823-day half-life. Radium is element 88 and radon is element 86, and 226 minus 222 is 4: the loss of two protons and two neutrons, which is what EPA says an alpha particle is made of.

5. 5

   Decay products, then lead-206

   Radon's decay products are solids that LANL says collect on dust in the air. The chain ends at lead-206, which EPA says is the stable end point.

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.

Radon was discovered in 1900, the year both LANL and PubChem give. Its history is tied to radium, which LANL says Madame Curie discovered in 1898 in pitchblende.

• 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.

As a gas at room temperature radon cannot be seen, but frozen it can. PubChem's summary says that when cooled to its solid state, radon glows yellow, and the glow becomes orange-red as the temperature is lowered.

Radon is a noble gas, and noble gases have little tendency to react. LANL calls radon essentially inert, and ATSDR says that since radon is a noble gas, it releases from any chemical bonds that attach it, which is why it can travel far enough to reach groundwater or the air.

The electron configurations show why. In PubChem's table krypton ends in 4s2 4p6 and radon in 6s2 6p6: each has a filled outer shell of eight electrons, the arrangement that gives an atom little reason to gain, lose or share electrons. PubChem lists the oxidation state of both krypton and radon as 0. This is the answer to the textbook question of why radon and krypton do not bond easily.

So "rarely" is the right word, not "never". LANL reports that fluorine reacts with radon to form a fluoride, lists oxidation states of 6, 2 and 0 for it, and notes that radon clathrates have also been reported. PubChem's radon record adds that radon fluoride (RnF) is the only confirmed compound of radon.

Very little today. PubChem's summary says radon is still primarily obtained through the decay of radium, and LANL says radon is still produced for therapeutic use by a few hospitals by pumping it from a radium source and sealing it in minute tubes, called seeds or needles, for application to patients. It adds that the practice has been largely discontinued, because hospitals can get seeds directly from suppliers.

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.

Radon in earth science: dating groundwater

PubChem's radon record names research uses in water. 222Rn has been used as a tool to date groundwater in combination with other isotopes or elemental ratios, such as helium/radon and xenon/radon amount ratios, and the interaction of radon with streams and rivers enables it to be used as a tracer in groundwater studies. It also notes that radon is present in some spring waters, such as those at Hot Springs, Arkansas. Neither use involves breathing it.

Radon forms wherever its parents are. EPA says radon is a radioactive gas that forms naturally when uranium, thorium, or radium, which are radioactive metals, break down in rocks, soil and groundwater, and that because radon comes naturally from the earth, people are always exposed to it. ATSDR describes the process: each atom of uranium or thorium decays or transforms about a dozen times, and radium and then radon are formed midway through these decay chains.

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.

Each property above has a practical side. Radon is a gas, so it can move. EPA says it can move up from the ground into buildings through openings in floors or walls that are in contact with the ground, and that it can accumulate in buildings. It is colorless, and WHO says it has no smell or taste, so nobody can sense it. Testing is the only way to know the radon level in a specific building.

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.