Heaviest Known element Og have valence electrons orbiting the nucleus as a gas (without a distinct shell)

Oganesson (Og) ( Z=118) is the recently discovered element which was produced by a fission reaction between Ca (Z = 20 & A = 48) and Cf (Z = 98 & A = 249). It's estimated  α-decay half-life is about  0.89 ms which make it's chemical studied nearly impossible. Hence it's chemical and physical properties has to be inferred from advanced relativistic quantum mechanical calculations. In the recent study conducted by Paul Jerabek, Bastian Schuetrumpf, Peter Schwerdtfeger, and Witold Nazarewicz, they employed the local spatial measure of fermion localization to arrive at a conclusion that in Og, the electron shells with  ℓ>0  show very large spin-orbit splittings smearing out of the one-particle  density, thus becoming more uniformly distributed over the entire atom  approaching the electron-gas regime in the valence region.  A direct consequence of this unusual property of Og is it's predicted large static dipole polarizability resulting in an increase in van der Waals interactions compared to  the lighter rare gases and a significant change in its chemical and  physical properties.

Source - https://doi.org/10.1103/PhysRevLett.120.053001