Name: Ununoctium
Symbol: Uuo
Atomic Number: 118
AtomicWeight: 293.000000
Family: Noble Gases
CAS RN: 54144-19-3
Description: A very short lived super heavy element, appearance unknown
State (25C): Unknown (Synthetic)
Oxidation states: unknown
Valence Electrons: 5f146d107s27p6

Boiling Point:  unknown
Melting Point:
Electrons Energy Level: unknown
Isotopes: unknown
Heat of Vaporization: unknown
Heat of Fusion: unknown
Density: unknown
Specific Heat: unknown
Atomic Radius: unknown
Ionic Radius: unknown
Electronegativity: unknown
Ununoctium is the temporary IUPAC name for the superheavy element having atomic number of 118, currently the highest atomic number assigned to a reputedly discovered element.  It has the temporary IUPAC element symbol Uuo.

Ununoctium probably shares similar properties of its group, the noble gases, resembling radon in its chemical proerties, and so some some researchers have referred to it as aka-radon.  It is probably the second radioactive gaseous element and the first standard semiconcuctive gas.

Ignoring nuclear instability due to radioactivity, scientists expect that ununoctium is much more chemically reactive than xenon or radon.  It would likely form stable oxides (UuoO3, etc.) as well as chlorides and fluorides.

The name ununoctium is a systematic element name, used as a placholder until the IUPAC decides on a name.

On October 9, 2006, researchers working at the Joint Institute for Nuclear Research (JINR) in Dubna, Russia, announced in Physical Review C that they had indirectly detected a total of three nuclei of ununoctium-294 (one in 2002 and two more in 2005) produced via collisions of californium-249 atoms and calcium-48 ions:

ununoctium1.jpg (4345 bytes)


Because of the very small fusion reaction probability (the fusion cross section is 0.5 pb = 510-41 m2) more than 41019 calium ions had to be shot at the californium to have only three fusion reactions.

The research team consisted of workers from JINR and the Lawrence Livermore National Laboratory in California, USA. The decay products of three atoms of ununoctium, not the atoms themselves, were observed in Dubna.  A half-life of 0.89 ms was observed: 294Uuo decays into 290Uuh by alpha decay.

The identification of the 294Uuo nuclei was verified by separately creating the putative daughter nucleus 290Uuh by means of a bombardment of 245Cm with 48Ca ions,

ununoctium2.jpg (4313 bytes)

and checking that the 290Uuh decay matched the decay chain of the 294Uuo nuclei.

The daughter nucleus 290Uuh is very unstable, decaying with a half-life of 14 milliseconds into 286Uuq, which may undergo spontaneous fission or undergo alpha decay into 282Uub, which will undergo spontaneous fission.


In 1999, researchers at Lawrence Berkeley National Laboratory had announced the discovery of elements 116 and 118, in a paper published in Physical Review Letters.

The researchers claimed to have performed the reaction:

ununoctium3.jpg (4218 bytes)

The following year, they published a retraction after other researchers were unable to duplicate the results.  In June 2002, the director of the lab announced that the original claim of the discovery of these two elements had been based on data fabricated by principal author Victor Ninov.

The American group had intended to name it ghiorsium after Albert Ghiorso before having to retract their claim.

2s2 2p6
3s2 3p6 3d10
4s2 4p6 4d10 4f14
5s2 5p6 5d10 5f14
6s2 6p6 6d10
7s2 7p6


Officially Unnamed and Officially Unfound.

In 1999, the team at Lawrence Berkley Labs published a paper in the journal Physical Review Papers proclaiming their discovery of element 118. The scientific community exploded, hoping that the decay time of 118 (eka-radon) would longer than that of 114. Element 116 was also synthesized during this reaction, which used cold fusion to fuse 108Pb and 86Kr atoms together.

However, this experiment has NOT been repeated successfully at other laboratories.  Lawrence Berkley Labs officially retracted their paper in 2001, saying that they had actually misinterpreted their data.  Despite this, efforts to produce element 118  have not halted, and element 118 may yet still be synthesized.

atom.gif (700 bytes)

Atomic Mass
293Uuo 293.21467  

Interactive Periodic Table