Question

What is the electron-pair and molecular geometry around the central S atom in thionyl chloride, \(\mathrm{SOCl}_{2} ?\) What is the hybridization of sulfur in this compound?

Short answer

The electron-pair geometry is tetrahedral, molecular geometry is trigonal pyramidal, and sulfur is sp³ hybridized.

Step-by-step solution

Determine the Total Number of Valence Electrons

Sulfur (S) has 6 valence electrons, oxygen (O) has 6 valence electrons, and each chlorine (Cl) atom has 7 valence electrons. The total number of valence electrons for SOCl₂ can be calculated as follows:\[ 6 ( ext{S}) + 6 ( ext{O}) + 2 \times 7 ( ext{each Cl}) = 26 \text{ electrons} \]

Draw the Lewis Structure

Distribute the 26 valence electrons around the S atom to form a stable molecule. Place S in the center, and attach O and Cl atoms. S will form a double bond with O (using 4 electrons) and single bonds with each Cl atom (using a total of 4 more electrons). The remaining electrons are placed as lone pairs on O and Cl. The structure should show no formal charges and a complete octet around each atom.

Determine the Electron-Pair Geometry

The central S atom has 4 regions of electron density (one double bond with O and two single bonds with Cl, plus one lone pair). According to VSEPR theory, four regions of electron density distribute in a tetrahedral shape.

Determine the Molecular Geometry

Since one of the four electron regions is a lone pair, the molecular shape is not tetrahedral. The presence of a lone pair results in a trigonal pyramidal geometry for the SOCl₂ molecule.

Identify the Hybridization of Sulfur

The hybridization of an atom can be identified by the number of electron regions around it. For the S atom in SOCl₂, which has 4 regions of electron density, the hybridization is \(sp^3\). This corresponds to a combination of one s orbital and three p orbitals.

Key concepts

VSEPR Theory

Valence Shell Electron Pair Repulsion (VSEPR) theory is a model used to predict the geometry of individual molecules based on the repulsions between electron pairs. In thionyl chloride, \( \mathrm{SOCl}_{2} \), the central sulfur atom is surrounded by several regions of electron density. Using VSEPR theory, we determine the shape of the molecule by considering the following:

• Electron-Pair Geometry: This is based on all regions of electron density (bonds and lone pairs) around the sulfur atom. In \( \mathrm{SOCl}_{2} \), there are three bonding pairs (one double bond to oxygen, two single bonds to chlorine) and one lone pair, making four regions of electron density. According to VSEPR, these four regions arrange themselves tetrahedrally to minimize repulsion.
• Molecular Geometry: This considers only the bonded atoms, ignoring lone pairs. Since one of the tetrahedrally-arranged regions is a lone pair, the actual layout of the atoms is a trigonal pyramidal shape. This results in a slightly less symmetric structure than tetrahedral, due to the lone pair's ability to push the bonds closer together.

The VSEPR theory simplifies complex molecular geometries into easy-to-predict shapes by only needing to count bonds and lone pairs, making it a cornerstone concept in chemistry.

Hybridization

Hybridization is a concept that enables us to describe the mixing of atomic orbitals on a central atom to explain the geometry of molecular bonding. In \( \mathrm{SOCl}_{2} \), the sulfur atom undergoes \(sp^3\) hybridization, which involves the following steps:

• Identification of Electron Regions: The sulfur atom in \( \mathrm{SOCl}_{2} \) has one double bond with oxygen, two single bonds with chlorine, and one lone pair, resulting in four regions of electron density. This configuration corresponds to tetrahedral electron-pair geometry.
• Mixing of Orbitals: To accommodate these four regions, one s orbital and three p orbitals from the sulfur atom hybridize to form four equivalent \(sp^3\) hybrid orbitals.
• Bond Formation: These \(sp^3\) hybrid orbitals then overlap with orbitals from oxygen and chlorine atoms to form the bonds in \( \mathrm{SOCl}_{2} \). The lone pair occupies one of these hybrid orbitals, leading to the shape predicted by VSEPR theory.

Understanding hybridization allows chemists to make predictions about molecular structure and reactivity based on the underlying atomic orbital interactions.

Lewis Structure

A Lewis structure is a diagrammatic method used to represent the bonding and electron distribution in a molecule. For \( \mathrm{SOCl}_{2} \), constructing a Lewis structure involves these steps:

• Count Valence Electrons: Calculate the total valence electrons available for \( \mathrm{SOCl}_{2} \) — sulfur has 6, oxygen also has 6, and each chlorine provides 7, summing up to 26 electrons.
• Arrange Atoms and Electrons: Place sulfur in the center (being the least electronegative), connect it with double bond to oxygen and single bonds to each chlorine. This uses eight electrons for bonds.
• Complete the Octets: Distribute the remaining electrons as lone pairs to fulfill the octet rule for each atom. Oxygen and both chlorines will have complete octets; sulfur typically exceeds the octet due to its larger size and availability of d orbitals.

Crafting a Lewis structure ensures that the arrangement of atoms and electrons respects the octet rule and reflects the actual molecule's structure as guided by VSEPR theory and hybridization concepts.