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This article is about an undiscovered element. Once it is discovered, this article will be edited with more information.



Atomic Number


Group, Period

18, 9

Electrons per shell




Date discovered


Location discovered


Atomic weight



Possible noble gas

Biunoctium, Buo, is the systematic temporary name of the very heavy theoretical element with 218 protons. It has been predicted to be a noble gas.

218 g

History Edit

Buo has the highest atomic number of any element whose atomic properties have been studied. Since it is very far in the periodic table and never has been made, we know very little about it, therefore, it is hard to actually find something with this title.

As we speak, the reason these names seem so familiar to others is because elements go under a systematic temporary element name, using Dog Latin, -a form of debased Latin- used by scientists before an element is given its permanent name.

Nuclear Properties

What follows is based on a first-order, liquid-drop assessment of where the outer boundary of the nuclear world is.

Assume cautious values for how many neutrons a nucleus with 218 protons can bind (high neutron dripline) and how few it can have before it fissions immediately regardless of how much the structure it can develop stabilizes it (low must-fission curve).  Assume, too, that anything that lasts long enough so that protons and neutrons can be treated as particles rather than collections of quarks (is causal) might be a nucleus.  Under these conditions, Buo isotopes are theoretically possible between Buo 664 and Buo 975 (see "The Final Element", this wiki).

Buo 664 through Buo 768 are expected to decay by beta emission if they don’t fission quickly.  Above that value of A, the confident neutron dripline, drops may decay by neutron emission before they can fission.  (Structural correction does not affect neutron emission.)  Isotopes lighter than Buo 697 need more than twice the  structural correction energy needed to prevent fission in worst-case nuclei in the A = 480 region(4).  Predicting whether or not the structure a nuclear drop can develop will allow it to survive for the 10^-14 sec required for it to bind an electron and so become an atomic nucleus is not usually possible at this time. 

Neutron shell closures have been predicted at N = 644, and 524(5).  The former may allow some nuclei in the vicinity of Buo 862; it requires only 2 MeV structural correction, but is 12% above the confident dripline.  The latter may allow some nuclei in the vicinity of Buo 742; it requires 14 MeV of structural correction, but lies below the confident dripline.  The band Buo 732 through Bbo 867 is the most probable location for Buo isotopes.  Buo 696 and lighter are implausible, while Buo 868 and heavier are highly unlikely.

1. "Decay Modes and a Limit of Existence of Nuclei"; H. Koura; 4th Int. Conf. on the Chemistry and Physics of Transactinide Elements; Sept. 2011.

2.  "Magic Numbers of Ultraheavy Nuclei"; V. Yu Denisov; Physics of Atomic Nuclei, v. 68, no. 7, pp 1133-1137; 2005.


Atomic Properties

Electron structure of Buo has not been studied closely, but it is likely to differ significantly from the conventional orbitals found in lower-Z nuclei. While only the innermost electrons would be qualitatively different, other electrons are likely to be quantitatively different from those in lower-Z atoms.  Buo is also large enough that nuclear shape may have an effect on electron structure, which might cause different isotopes of Buo to be chemically different. (Which means it is no longer an element in the chemical sense.)   Predictions of atomic or chemical properties of Buo are risky.


Ions of this element may form when material from roughly 1 km depth is ejected from a disintegrating neutron star during a merger. It is probably impossible for lighter isotopes to form in this way.


References Edit

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