The F – S – F bond angles in SF6 are
A) 90° and 180°
B) 109.5°
C) 120°
D) 180°
E) 90° and 120°
The Correct Answer and Explanation is :
The correct answer is A) 90° and 180°.
Explanation:
SF₆ (sulfur hexafluoride) is a molecule in which a central sulfur (S) atom is bonded to six fluorine (F) atoms. The shape of the SF₆ molecule can be understood using VSEPR (Valence Shell Electron Pair Repulsion) theory, which predicts the geometry of molecules based on repulsions between electron pairs around the central atom.
In SF₆, sulfur has six bonding pairs of electrons and no lone pairs. The six fluorine atoms are arranged around sulfur in such a way that the repulsions between these electron pairs are minimized. This leads to an octahedral geometry.
In an octahedral geometry:
- The six bonds are arranged symmetrically around the central atom.
- Four fluorine atoms are placed in the same plane, forming a square around the sulfur atom, and two fluorine atoms are located along the axis perpendicular to this plane.
This arrangement results in two distinct bond angles:
- 90° bond angles: These occur between any two adjacent fluorine atoms in the octahedral structure, such as between atoms in the equatorial (square planar) plane and atoms in the axial positions.
- 180° bond angles: These occur between two fluorine atoms positioned directly opposite each other along the axial positions.
Thus, the F-S-F bond angles in SF₆ are 90° (between adjacent fluorine atoms) and 180° (between opposite fluorine atoms). There are no 120° or 109.5° bond angles, which are characteristic of different molecular geometries like trigonal planar or tetrahedral, respectively.
The octahedral geometry is also highly symmetrical, contributing to SF₆ being non-polar despite its polar S-F bonds, as the dipoles cancel out due to the symmetric shape.