Atomic Number


Group, Period

18, 9

Electrons per shell




Date discovered


Location discovered


Atomic weight



Possible noble gas

Biunocton, Buo, is the systematic temporary name of the theoretical element with 218 protons. It is unlikely that this element exists.

218 g

History Edit

Buo has the highest atomic number of any element whose atomic properties have been studied. At one time, it was thought that Buo ended the ninth period, something now thought unlikely.

Nuclear Properties

No predictions for half-life or decay modes are available for elements with Z > 175. It is possible to determine a boundary in the (Z,A) {or (Z,N)} plane outside of which no nuclides are possible, as detailed in "The Final Element", this wiki.

A nuclear drop containing 218 protons and more than 758 neutrons must decay by neutron emission with a half-life under 10^-14 sec. A drop with 218 protons and fewer than 445 neutrons must decay by spontaneous fission with a half-life under 10^-14 sec. Nuclear drops in the band from Buo 976 to Buo 663 are not required to decay either by neutron emission or by fission, so it is possible they will survive the 10^-14 sec needed for them to become nuclides.

The boundary described above was arrived at by applying large factors of safety to quantities which have been predicted. By looking at which factors apply to a particular (Z,A) point, it is possible to make a qualitative guess how likely it is that (Z,A) is a nuclide. Details of this method are given in "Nuclear Guesswork", this Wiki. What follows should not be considered predictions, only guesses as to what might be. Likelihood that a nuclide can exist are given in four categories: likely, unlikely, improbable, and not impossible.

Nuclear drops in the bands Buo 976 to Buo 967 and Buo 867 to Buo 846 are likely to decay by neutron emission but are stable against fission. Nuclides in these bands are unlikely. Drops in the bands Buo 966 to Buo 868 and Buo 845 to Buo 808 are likely to decay by neutron emission and require a moderate amount of structural correction energy. Nuclides in these bands are improbable. Drops in the band Buo 807 to Buo 728 are unlikely to decay by neutron emission but require moderate structural correction. Nuclides in this band are unlikely. Drops in the band Buo 727 to Buo 663 are unlikely to decay by neutron emission but require large structural correction. Nuclides in this band are improbable.


Beyond Z = 175, the neutron dripline can only be constrained within a minimum value, Nc(Z) at which neutron decay becomes unlikely and a maximum value, Np(Z), at which it becomes inevitable. Drops Buo 976 to Buo 807 lie within this band. Since a disintegrating neutron star can supply pieces of nuclear matter of the right size (see "Neutron Star", this wiki), any isotope in that band is possible if the actual neutron dripline lies at the right location. No single dripline location will cause all isotopes to form, though.

Since 218 < 1.25*175, chances are that the actual dripline lies close to Nc(218).

Drops Buo 806 to Buo 663 require at least one beta decay from a mother nucleus which is itself unlikely at best. It is unlikely for isotopes in this band to form.

Chemical propertiesEdit

The nuclear charge of Buo is so great that stationary-state orbital theory cannot describe its electrons. In addition, both nuclear size and nuclear shape may affect its electron structure. If these effects are small, and if the assumptions made in "Period 9 Elements" (this wiki) are valid, Buo will be a 9th period d-block metal.


References are given in the articles cited.


References (retained as background) Edit

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