Question

Give reasons for the following: (a) \(\mathrm{XeF}_{2}\) and \(\mathrm{ClF}_{3}\) have same hybridisation but different geometries (b) \(\mathrm{SnCl}\), and \(\mathrm{H}_{2} \mathrm{O}\) have same geometry but different hybridization

Short answer

(a) Although XeF2 and ClF3 have the same hybridization (sp3d), they have different geometries due to the different arrangements of bonded atoms and lone pairs around the central atom; linear for XeF2 and T-shape for ClF3. (b) SnCl2 and H2O have the same angular geometry due to the presence of two bonded atoms and one or two lone pair of electrons around the central atom, even though they have different hybridizations (sp2 for SnCl2 and sp3 for H2O).

Step-by-step solution

Determine hybridization (a)

Both \(\mathrm{XeF}_{2}\) and \(\mathrm{ClF}_{3}\) have hybridisations of sp3d. The hybridization of Xe in XeF2 is sp3d due to 2 bond pairs and 3 lone pairs of electrons. For ClF3, Cl is sp3d due to 3 bond pairs and 2 lone pairs of electrons.

Determine geometry (a)

Although \(\mathrm{XeF}_{2}\) and \(\mathrm{ClF}_{3}\) have same hybridization, their geometries are different due to different arrangements of bond pairs and lone pairs around the central atom. \(\mathrm{XeF}_{2}\) has a linear shape (180 degrees bond angle) since there are 3 lone pairs that occupy the equatorial position and two F atoms occupy the axial positions. On the other hand, \(\mathrm{ClF}_{3}\) has a T-shape (less than 90 degrees bond angle) due to 2 lone pairs and 3 bond pairs of electrons.

Determine hybridization (b)

\(\mathrm{SnCl}_{2}\) and \(\mathrm{H}_{2} \mathrm{O}\) have different hybridisation. Sn in SnCl2 has sp2 hybridisation due to 2 bond pairs and 1 lone pair of electrons. However, O in H2O is sp3 hybridised due to 2 bond pairs and 2 lone pairs.

Determine geometry (b)

Despite different hybridizations, \(\mathrm{SnCl}_{2}\) and \(\mathrm{H}_{2} \mathrm{O}\) have the same bend (angular) molecular geometry because they both have two bonded atoms and one or two lone pair of electrons around the central atom. Due to electron-electron repulsion, the shape of both molecules is bent.

Key concepts

Chemical Bonding

Understanding the basics of chemical bonding is key to understanding molecular geometry and hybridization. Atoms bond together to form molecules by sharing or transferring electrons to achieve stability, often described as the octet rule. There are three primary types of chemical bonds:

• Ionic bonds: Formed when one atom gives up one or more electrons to another atom, resulting in a pair of oppositely charged ions.
• Covalent bonds: Occur when atoms share pairs of electrons. The number of shared electron pairs correlates with the type of covalent bond—single, double, or triple bonds.
• Metallic bonds: These involve a sea of electrons that are shared and delocalized among a lattice of metal atoms.

Hybridization is a concept within chemical bonding, which describes how atomic orbitals mix to form new hybrid orbitals. This mixing results in the geometry necessary for the bonding properties of the atom. In our exercise, the compounds were analyzed based on their hybridizations to understand their molecular geometries.

VSEPR Theory

The Valence Shell Electron Pair Repulsion (VSEPR) theory is fundamental to predicting the molecular shape of compounds. It states that electron pairs around a central atom will arrange themselves as far apart as possible to minimize repulsion.

VSEPR theory is used to determine the molecular geometry of a molecule based on the number of bonding pairs and lone pairs of electrons. For example, in the case of , we apply this theory to understand why, despite having the same hybridization, they exhibit different geometries.

Electron Pair Repulsion

At the core of VSEPR theory is the concept of electron pair repulsion. Electrons have a negative charge and will naturally repel each other. Electron pairs, both bonding and non-bonding (lone pairs), repel one another. This repulsion affects the overall geometry of the molecule.

The degree of repulsion between different pairs of electrons can vary; lone pairs additionally repel more strongly than bonding pairs. This aspect explains the difference in the molecular shapes of and , as highlighted in the exercise solutions, where the number and types of electron pairs led to variations in molecular geometry.

Molecular Shape

The molecular shape is directly influenced by the hybridization of the central atom and the distribution of electron pairs around it. Depending on the number of bond pairs and lone pairs, molecules can have shapes such as linear, bent, trigonal planar, tetrahedral, and more.

In the exercise, we saw that and have different hybridizations yet the same angular geometry. This is because the electron pair repulsion and the arrangements of the electrons are what ultimately determine the molecules' shapes. Recognizing electron pair geometry and molecular shape can help explain the properties and behaviors of different molecules in various chemical contexts.