Trinilhexium, Tnh, is the temporary name for element 306.NUCLEAR
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 306 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, Tnh isotopes are theoretically possible between Tnh 1375 and Tnh 1451 (see "The Final Element", this wiki).
Nuclear drops in this band have at least 272 more neutrons than the limit at which neutron decay is expected to begin (confident neutron dripline). All may decay by neutron emission faster than they can fission. Tnh drops also require at least 1.7 times the structural correction energy required to prevent fission in worst-case nuclei in the A = 480 region(1). Predicting whether or not the structure a nuclear drop can develop will allow the drop to survive for the 10^-14 sec required for it to bind an electron and so become an atomic nucleus is not possible at this time, but it is likely that all Tnh drops that don’t decay quickly by neutron emission will fission quickly regardless of structure.
Tnh is almost, but not quite, impossible.
Conventional techniques for computing an element's electron structure cannot be used to study Tnh. Its nuclear size is so large that the concept of time-invariant orbitals no longer applies. In addition, it is so large that nuclear shape probably causes different isotopes of Tnh to have different electronic structures. (It is no longer an element in the chemical sense.)
If it can exist at all, ions of this element may form when material from roughly 1 km depth is ejected from a disintegrating neutron star during a merger.
REFERENCES1. "Decay Modes and a Limit of Existence of Nuclei"; H. Koura; 4th Int. Conf. on the Chemistry and Physics of Transactinide Elements; Sept. 2011.