Unbihexium

Unbihexium ( /ˌuːnbaɪˈhɛksiəm/), also known as eka-plutonium or element 126, is a hypothetical chemical element with atomic number 126 and symbol Ubh. It is of interest because of its location at the peak of the hypothesized island of stability.

1 History
2 Target-projectile combinations leading to Z=126 compound nuclei
3 Stable unbihexium
4 Predicted chemistry
5 See also
6 References

History

The first attempt to synthesize unbihexium was performed in 1971 by Bimbot et al. using the hot fusion reaction:

$\,^{232}_{90}\mathrm{Th} %2B \,^{84}_{36}\mathrm{Kr} \to \,^{316}_{126}\mathrm{Ubh} ^{*} \to \ no \ atoms$

A high energy alpha particle was observed and taken as possible evidence for the synthesis of unbihexium. Recent research suggests that this is highly unlikely as the sensitivity of experiments performed in 1971 would have been several orders of magnitude too low according to current understanding.

To date, no other attempt has been made to synthesize unbihexium.

Target-projectile combinations leading to Z=126 compound nuclei

The table below contains various combinations of targets and projectiles (both at max no. of neutrons) which could be used to form compound nuclei with Z=126. The only practical isotopes of unbihexium that would be considerably longer-lived than others are ³¹⁰Ubh and ³²²Ubh.

Target	Projectile	CN	Attempt result
¹⁸²Hf	¹³⁶Xe	³¹⁸Ubh	Reaction yet to be attempted
²³²Th	⁸⁴Kr	³¹⁶Ubh	Failure to date
²⁴³Cm	⁶⁷Zn	³¹⁰Ubh	Reaction yet to be attempted
²⁴⁸Cf	⁶²Ni	³¹⁰Ubh	Reaction yet to be attempted
²⁴⁹Cf	⁶¹Ni	³¹⁰Ubh	Reaction yet to be attempted
²⁵¹Es	⁵⁹Co	³¹⁰Ubh	Reaction yet to be attempted
²⁵⁴Fm	⁵⁶Fe	³¹⁰Ubh	Reaction yet to be attempted
²⁵⁷Md	⁵³Mn	³¹⁰Ubh	Reaction yet to be attempted
²⁶⁰Rf	⁵⁰Ti	³¹⁰Ubh	Reaction yet to be attempted
²⁷¹Sg	⁴⁸Ca	³¹⁹Ubh	Reaction yet to be attempted

Another way to synthesize unbihexium would be to overshoot it by fusion of ¹³⁰Te and ²⁰⁴Hg; successive alpha decay of the compound nucleus ³³⁴Utb would land right on ³²²Ubh (predicted to be relatively stable). ¹³⁰Te constitutes about 34% of the natural element; however, ²⁰⁴Hg only constitutes about 7% of natural mercury.

Stable unbihexium

Calculations according to the Hartree-Fock-Bogoliubov Method using the non-relativistic Skyrme interaction have proposed Z=126 as a closed proton shell. In this region of the periodic table, N=184 and N=196 have been suggested as closed neutron shells. Therefore the isotopes of most interest are ³¹⁰Ubh and ³²²Ubh, for these might be considerably longer-lived than other isotopes.

Predicted chemistry

Unbihexium is predicted to belong to a new block of valence g-electron atoms, although the g-block's position left of the f-block is speculative. The expected electron configuration is [Uuo]5g⁶ 8s² although there may be a smearing out of the energies of 5g, 6f and 7d orbitals.

Recent calculations have suggested a stable monofluoride UbhF may exist, resulting from a bonding interaction between the 5g orbital on Ubh and the 2p orbital on fluorine.^[1] Other predicted oxidation states include III, IV, VI, and VIII.