If the two heaviest elements in the periodic table had a chance to react, they could form a stable pentatomic molecule, according to the first computational study of its type to examine the properties of a molecule composed of tennessine (element 117) and oganesson (element 118) (Theor. Chem. Acc. 2021, DOI: 10.1007/s00214-021-02777-2). The study explores the chemistry of a molecule that has yet to be created and may guide future experiments. It also offers a test case for examining the effects of relativity, such as spin-orbit coupling, which strongly affects heavy elements and causes complex shifts in their electronic energy levels. To probe the properties of OgTs4, a team led by Gulzari L. Malli of Simon Fraser University compared the results of relativistic and nonrelativistic analyses, both of which are computationally intense. The relativistic computations indicate that OgTs4 is a stable molecule, likely to adopt tetrahedral geometry, which for this molecule is roughly 1 eV more stable than the square planar version. Omitting the effects of relativity leads to several erroneous predictions, most notably that OgTs4 isn’t stable enough to be bound. The study shows that for the heaviest elements, relativity must be addressed rigorously, says Paul J. Karol, a Carnegie Mellon University scientist, who was not involved in the work. “Chemical intuition doesn’t help because relativity scrambles everything,” he says.