Why can sulfur form sulfur tetrafluoride and sulfur hexafluoride?

Sulfur is able to form stable compounds like sulfur tetrafluoride (SF₄) and sulfur hexafluoride (SF₆) primarily because it is a third-period element, which allows it to accommodate more than the standard octet of electrons.12

While early chemical theories suggested that sulfur achieves this "hypervalence" by utilizing its 3d orbitals to expand its octet, modern molecular orbital (MO) theory provides a more accurate explanation. In this view, the bonding in molecules like SF₆ is described through delocalized molecular orbitals that distribute the bonding effect of electron pairs over all the atoms in the molecule. This delocalization eliminates the necessity of invoking 3d orbital participation as a primary requirement for bonding.3

Additionally, the ability of sulfur to form these compounds is influenced by its size and polarizability. As a larger atom compared to oxygen, sulfur can coordinate with a greater number of ligands. While sulfur can form these stable hypervalent structures, it is limited by the size of the coordinating atoms; for instance, sulfur hexaiodide (SI₆) is not known because the iodine atom is too large to accommodate the necessary coordination.24