118OgOganesson294[Rn] 5f¹⁴ 6d¹⁰ 7s² 7p⁶
unknown predicted to be noble gas

Oganesson

Oganesson is IUPAC's name for the transactinide element with the atomic number 118 and element symbol Og. It is also known as eka-radon or element 118, and on the periodic table of the elements it is a p-block element and the last one of the 7th period. Oganesson is currently the only synthetic member of group 18.

Properties

At a glance

Atomic number
118
Atomic mass
294 u
Phase
Solid
Density
4.95 g/cm³
Melting point
Unavailable
Boiling point
350 K
First ionization energy
Unavailable
Electronegativity
Unavailable
Electron affinity
5.40318 kJ/mol
Molar heat capacity
Unavailable
Period
7
Appearance
Unavailable

Conditions and isotopes affect measured properties. Some properties of short-lived elements are predicted. Electronegativity uses the Pauling scale.

Electronic structure

Predicted configuration. These hydrogen-like orbitals omit oganesson’s strong relativistic effects. Every orbital of each visible subshell is shown: in Shapes as the surface holding half its probability, with light and dark shades for opposite signs of the wavefunction; in Cloud as dots where its electrons are likely to be. Sizes are stepped by shell, like the Shell model.

Electrons by shell
Electron configuration

86 is the [Rn] core total across six shells.

Preparing the orbital view…

118 protons176 neutrons

Oganesson-294: its most common form in nature, or its longest-lived if it has none. The nucleus is drawn far too big: it’s about 100,000 times smaller than the atom.

Superheavy elements

The island of stability

Every element heavier than lead is radioactive, and the heavier they get, the faster they fall apart. Oganesson’s longest-lived known form, Oganesson-294, has a half-life of 580 microseconds. Yet physicists predict that a little further on there is an “island” of heavier nuclei that should last much longer.

The longest-lived form of each elementFor each element from lead onwards, the half-life of its longest-lasting known isotope: how long it takes for half of a sample to decay. The scale is logarithmic, so each step up is ten times longer. Hover or tap a point to see it.
Age of the universeA million yearsA yearA dayA secondA millisecondPbUFmDsOg

Oganesson-294 half-life 580 microseconds

From uranium, which has lasted since before the Earth formed, lifetimes plunge. But from rutherfordium (104) on, the fall flattens out to seconds and minutes. Those longest-lived forms are also the most neutron-rich ones made so far: more neutrons help, just as the island idea predicts.

Walk towards the islandEach square is one nuclide: a particular number of protons (which element it is) and neutrons. Darker squares last longer. Squares with a dashed outline were measured from only a few atoms, so their half-lives are very uncertain. Tap a square, or use the buttons, to see it.

120119OgTsLvMcFlNhCnRgDsMtHsBhSgDbRfLrNo150160170180184Predicted island
  • Under 1 ms
  • 1 ms – 1 s
  • 1 s – 1 min
  • 1 min – 1 h
  • 1 h – 1 day
  • Over a day
  • Very uncertain

Oganesson-294

118 protons and 176 neutrons. Half-life 580 microseconds; it gives off an alpha particle. That’s 8 neutrons short of the island’s predicted centre at 184.

Along each row, adding neutrons mostly makes the nucleus last longer. But no one has made a superheavy nucleus with more than 177 neutrons: they are made by fusing two lighter nuclei, and lighter nuclei don’t have enough neutrons to spare.

Why an island?

  • Magic numbers

    Protons and neutrons fill shells in the nucleus, much as electrons fill shells around it. Full shells are extra stable: lead-208, with 82 protons and 126 neutrons, is doubly “magic” and never decays.

  • The next full shells

    Theory predicts the next magic numbers at about 114 protons and 184 neutrons. Estimates of how long nuclei there would last range from minutes to far longer; no one knows.

  • Made an atom at a time

    Superheavy elements are made by firing a beam of one element at a target of another for weeks. Only a handful of atoms of the heaviest, like oganesson, have ever been seen.

Half-lives and decay modes from the IAEA Live Chart of Nuclides (ENSDF). An element’s longest-lived form counts only half-lives measured to better than their own size; values from only a few atoms are shown on the map with a dashed outline. The island’s outline is a sketch of where theory puts it, not a measurement.

Keep exploring

Explore the stories, imagery, and reference data in more depth. Properties with no value in the reference are marked unavailable.