Spin−Orbit Effects, VSEPR Theory, and the Electronic Structures of Heavy and Superheavy Group IVA Hydrides and Group VIIIA Tetrafluorides. A Partial Role Reversal for Elements 114 and 118

Relativistic effective core potentials and spin−orbit operators are used in relativistic configuration interaction calculations to explore the effects of spin−orbit coupling on the electronic structures of atoms and molecules of elements 114 and 118. The monohydrides of group IVA and the tetrafluorides of group VIIIA are examined in order to provide examples of trends within families among the various periods. The spin−orbit effect is found to play a dominant role in the determination of atomic and molecular properties. Several nonintuitive consequences of spin−orbit coupling are presented, including the depiction of element 114 as a closed-shell “noble” atom and the suggestion that the VSEPR theory is inadequate to describe the geometry of the rare gas tetrafluoride, (118)F4.