The Lewis structure for SF4 is shown. What is the electron-pair geometry and the molecular geometry around the central atom?
Electron Pair Geometry:
Molecular Geometry:
The Correct Answer and Explanation is :
The electron-pair geometry of sulfur tetrafluoride (SF₄) is trigonal bipyramidal, while its molecular geometry is seesaw.
Electron-Pair Geometry: Trigonal Bipyramidal
In SF₄, the central sulfur atom has five electron pairs: four bonding pairs from the fluorine atoms and one lone pair. According to Valence Shell Electron Pair Repulsion (VSEPR) theory, five electron pairs arrange themselves in a trigonal bipyramidal geometry to minimize electron-electron repulsion. This arrangement consists of three equatorial positions at 120° angles and two axial positions at 90° angles relative to the equatorial plane. citeturn0search11
Molecular Geometry: Seesaw
The presence of the lone pair alters the molecular geometry. Lone pairs occupy equatorial positions because they experience less repulsion compared to axial positions. This placement results in a seesaw shape, where three fluorine atoms occupy the equatorial positions and one occupies an axial position. The bond angles are approximately 173.1° between axial fluorines and 101.6° between equatorial fluorines, deviating from the ideal 90° and 120° due to the influence of the lone pair. citeturn0search10
Explanation
In SF₄, sulfur has five valence electrons, and each fluorine atom contributes one electron, totaling five bonding pairs. The lone pair on sulfur occupies one of the equatorial positions, leading to the seesaw molecular geometry. This configuration minimizes electron-electron repulsion by placing the lone pair in an equatorial position, where it experiences less repulsion compared to an axial position. The bond angles are adjusted from the ideal trigonal bipyramidal angles due to the presence of the lone pair, which exerts greater repulsion than bonding pairs, causing the axial fluorines to be pushed closer together and the equatorial fluorines to be pushed apart.
For a visual explanation, you might find the following video helpful:
videoSF4 Electron Geometry (Sulfur tetrafluoride)turn0search0