Oganesson · element 118
The heaviest element known, a noble gas on paper that is probably a solid, named for a living scientist
Key facts
Oganesson is the last box on the periodic table, element 118, the end of the seventh row. Only about five atoms have ever been detected, each surviving for less than a thousandth of a second. It is named after Yuri Oganessian, the physicist who led the Dubna programme responsible for the six heaviest elements known, and only the second living person, after Glenn Seaborg, to be so honoured.
Oganesson sits under radon in group 18, the noble gases, and its name ends in -on like theirs. But almost every calculation says it will not behave like one. It is predicted to be a solid at room temperature, to be more reactive than radon, and to have electrons so scrambled by relativity that the neat shell structure of lighter atoms barely applies.
Where it is found
Oganesson does not exist in nature and cannot. Its only known isotope, oganesson-294, has a half-life of well under a millisecond. Every atom that has ever existed was made at Dubna, and the total stands at about five. Nothing on Earth has ever been rarer.
It is made by firing calcium-48 at californium-249, itself a synthetic element produced in reactors at Oak Ridge. Even with weeks of continuous bombardment, a successful fusion happens perhaps once a month. The fused nucleus sheds three neutrons to become oganesson-294, which within a fraction of a millisecond emits an alpha particle and becomes livermorium-290. That alpha, and those that follow, are the only evidence that oganesson was ever there.
How it was discovered
A Berkeley team claimed element 118 in 1999, but the result could not be reproduced, was retracted in 2001, and the laboratory concluded that one researcher had fabricated the data. The genuine discovery came from Dubna. Oganessian's team, working with Lawrence Livermore, recorded a first candidate event in 2002 and two more in 2005, publishing in 2006.
IUPAC accepted the discovery in December 2015 and approved the name oganesson, symbol Og, in November 2016. Oganessian had pioneered the hot fusion method with calcium-48 beams that produced elements 114 to 118, and before that developed the cold fusion technique GSI used for elements 107 to 112. Naming an element after him recognised a career that shaped the whole field.
What we use it for
Oganesson has no uses and never will, unless a far more stable isotope is found. With about five atoms ever made, each lasting under a millisecond, no chemistry is possible and no physical property can be measured directly.
Its importance is as the extreme case. Oganesson tests whether the periodic table still means anything when an atom has 118 electrons moving at a large fraction of the speed of light. Calculations published in 2018 suggest that in oganesson the electrons are so smeared out that distinct shells almost disappear. Other predictions say it should be a solid with a boiling point not far above room temperature, should attract an extra electron rather than repel one, and could form fluorides more readily than radon.
Reading the numbers
The atomic mass of 294 is the only isotope known. Every other figure is a calculation. The predicted boiling point of about 350 kelvin, roughly 77 degrees Celsius, is startling for a noble gas; radon boils at minus 62 degrees. If the prediction holds, oganesson would be a solid or liquid on a warm day, which is why the phase is listed as solid. The predicted density of about 5 grams per cubic centimetre refers to that solid.
The configuration [Rn] 5f14 6d10 7s2 7p6 is a closed shell, exactly what group 18 requires. From helium to radon a closed shell means an atom that ignores its neighbours. In oganesson, relativity loosens the outermost 7p electrons so much that the atom should be easily polarised and attract other atoms through unusually strong dispersion forces. That is why theorists predict a solid rather than a gas, and why oganesson is expected to be by far the most reactive noble gas.
Safety and the environment
Oganesson is radioactive and lasts less than a millisecond. About five atoms have ever existed, all inside a shielded accelerator at Dubna, and all decayed immediately. It cannot be stored, released or transported. There is no oganesson in the environment and no possible way for anyone to be exposed.
Did you know?
- Only about five atoms of oganesson have ever been detected, making it the rarest element that has ever existed.
- Yuri Oganessian is only the second person, after Glenn Seaborg, to have an element named after him while alive.
- Oganesson is predicted to be a solid at room temperature, unlike every other noble gas, with a boiling point around 77 degrees Celsius.
- Calculations published in 2018 suggest oganesson's electrons are so smeared out by relativity that distinct shells almost vanish.
- Oganesson completes period 7 of the periodic table; the next element, 119, would begin an entirely new row.
- Oganesson-294 decays in under a millisecond, and the only evidence for each atom is the chain of alpha particles it leaves behind.
More in the superheavy elements
The nearest neighbours of oganesson in the family, by atomic number.
See all 15 superheavy elements on one page, or browse all 118 elements. Also listed under the noble gases.
Frequently asked questions
Is oganesson a gas?
Probably not. Although it sits in group 18 with the noble gases, calculations predict it would be a solid at room temperature with a boiling point around 77 degrees Celsius. This cannot be tested, because only about five atoms have ever existed and each lasted less than a millisecond.
Who is oganesson named after?
Yuri Oganessian, the physicist who led the superheavy element programme at the Dubna laboratory in Russia and developed the techniques used to make elements 114 to 118. He is the second living person to have an element named after him, following Glenn Seaborg.
How many atoms of oganesson have been made?
About five, all at Dubna between 2002 and 2012 or so, produced by firing calcium-48 at californium-249. Each was identified only through its chain of alpha decays.
Is oganesson the heaviest element?
Yes. With 118 protons it is the heaviest element ever made and the last in period 7 of the periodic table. Laboratories in Russia, Japan, Germany and China are attempting to make elements 119 and 120, but none has succeeded yet.
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Written by Anthony. Updated September 2026. Numerical data from Periodic-Table-JSON (CC BY-SA), cross-checked against the Oganesson reference article. Spotted an error? Tell us.