Using the VSEPR Model to Predict Molecular Geometry

Q1. Using the VSEPR model, predict the electron-domain and molecular geometries of (a) ClF3, (b) SO42−.

Background

Topic: VSEPR Theory (Valence Shell Electron Pair Repulsion Theory)

This question tests your understanding of how to use the VSEPR model to predict the shapes of molecules and polyatomic ions based on the number of electron domains (bonding and lone pairs) around a central atom.

Key Terms and Formulas

• Electron Domain: A region around a central atom where electrons are likely to be found; includes both bonding pairs (single, double, or triple bonds count as one domain each) and lone pairs.

• Electron-Domain Geometry: The arrangement of electron domains around the central atom.

• Molecular Geometry: The arrangement of only the atoms (not lone pairs) in a molecule.

• VSEPR Notation: ABxEy, where A = central atom, B = bonded atoms, E = lone pairs.

Step-by-Step Guidance

1. For each molecule or ion, draw the Lewis structure to determine the number of bonding pairs and lone pairs on the central atom.

2. Count the total number of electron domains (bonding pairs + lone pairs) around the central atom.

3. Use the VSEPR table to determine the electron-domain geometry based on the total number of domains.

4. Determine the molecular geometry by considering only the positions of the atoms (ignore lone pairs for this step).

Try solving on your own before revealing the answer!

Final Answer:

(a) ClF3: Electron-domain geometry is trigonal bipyramidal; molecular geometry is T-shaped. (b) SO42−: Electron-domain geometry is tetrahedral; molecular geometry is also tetrahedral.

These results are based on the number of bonding and lone pairs around the central atom as determined by the Lewis structure and VSEPR theory.