Molecular Geometry of Sulfur Tetrafluoride (SF4)
The molecular formula of sulfur tetrafluoride (SF4) indicates that the compound has one sulfur atom and four fluorine atoms. Sulfur is located in Group 16 of the periodic table and has six valence electrons. Fluorine is located in Group 17 and has seven valence electrons. Fluorine requires one electron to complete its octet and achieve the electron configuration of its nearest neighbor, neon. Sulfur and fluorine will combine to form four S-F single bonds. Sulfur will use four valence electrons to bond with the four fluorine atoms. Hence, it will have one lone pair of electrons, while each fluorine atom will have six [1-4].
Lewis structure is used to show the bond formation in sulfur tetrafluoride. Sulfur is the least electronegative of the two. So, it will lie at the center of the molecule. Dash lines represent the four S-F single covalent bonds. Dots represent the lone pairs.
VSEPR theory is used to predict the shape of the SF4 molecule. According to this theory, the central sulfur atom has a steric number of 5. It has five valence atomic orbitals forming five sp3d hybridized orbitals – one 3s orbital, three 3p orbitals, and one 3d orbital. Four hybrid orbitals overlap with fluorine’s 2p orbitals, and the fifth contains a lone pair.
The electron geometry of SF4 is trigonal bipyramidal. However, its molecular geometry is different. Because of the single lone pair, its shape will be a distorted tetrahedron or ‘seesaw’. In a trigonal bipyramidal molecule, the two bonds in the axial locations form a 180° angle. The two bonds in the equatorial positions form a 120° angle. However, the lone pair in sulfur changes the bond angles from 120° to 102° and from 180° to 173°. The VSEPR notation of SF4 is AX4E1.