What is the molecular geometry of the thiosulfate ion, S2O32–?
A) tetrahedral
B) trigonal bipyramidal
C) pyramidal
D) bent
E) square planar
The Correct Answer and Explanation is :
The correct molecular geometry of the thiosulfate ion, S₂O₃²⁻, is A) tetrahedral.
Explanation:
To determine the molecular geometry of the thiosulfate ion, we need to consider the following:
- Lewis Structure: The thiosulfate ion (S₂O₃²⁻) consists of two sulfur atoms and three oxygen atoms, with a -2 charge. The central sulfur atom is bonded to the three oxygens in a manner that creates a resonant structure, with the sulfur-oxygen bonds being a mixture of single and double bonds.
- Electron Domains: To understand the geometry, we first need to count the electron domains around the central sulfur atom. Each bond (single or double) to an oxygen counts as one electron domain. In the thiosulfate ion, one sulfur atom is bonded to two oxygen atoms via single bonds, and to the third oxygen atom through a double bond. This results in three electron domains around the central sulfur atom.
- Electron Geometry: The electron geometry is determined by the number of electron domains around the central atom. In this case, with three bonding regions, the electron geometry is trigonal planar.
- Molecular Geometry: Despite the trigonal planar electron geometry, the presence of lone pairs or multiple bonds must also be considered. In the thiosulfate ion, the geometry is tetrahedral due to the specific arrangement of bonding and lone pairs, resulting in a spatial distribution of the bonds that is consistent with a tetrahedral shape.
- Bond Angles: The bond angles in a tetrahedral geometry are approximately 109.5°. In the case of S₂O₃²⁻, the arrangement of the atoms reflects this geometry, as the negative charge is distributed across the structure in a manner that supports a tetrahedral bond arrangement.
Thus, the thiosulfate ion adopts a tetrahedral molecular geometry.