Molecular Geometry Lecture Notes

Importance of Molecular Geometry

• Understanding 3D arrangement of molecules is crucial for predicting chemical behavior.

VSEPR Model

• VSEPR: Valence Shell Electron Pair Repulsion.
• Used to predict shape of a molecule.
• Atoms are surrounded by electron clouds that repel each other, leading to specific geometries.

Electron Clouds and Energy

• Electron clouds act like magnets of like charge; repel each other.
• Lower energy achieved by maximizing distance between electron clouds.

Hybridization and Molecular Geometry

Hybridization Basics

• s, p, and d orbitals:
  • Each energy level has 1 s, 3 p, and 5 d orbitals.
• Hybridization relates to number of electron domains.

Examples of Molecular Geometries

Linear Geometry

• Example: Carbon Dioxide (CO2)
  • Carbon has 2 electron domains, sp hybridization.
  • Linear geometry with 180-degree bond angles.

Trigonal Planar Geometry

• Example: Boron Trifluoride (BF3)
  • Boron has 3 electron domains, sp2 hybridization.
  • Trigonal planar geometry with 120-degree bond angles.

Tetrahedral Geometry

• Example: Methane (CH4)
  • Carbon has 4 electron domains, sp3 hybridization.
  • Tetrahedral geometry with 109.5-degree bond angles.

Trigonal Bipyramidal Geometry

• Atoms with 5 electron domains are sp3d hybridized.
• Geometry involves both 90 and 120-degree bond angles.

Octahedral Geometry

• Atoms with 6 electron domains are sp3d2 hybridized.
• All bond angles are 90 degrees.

Influence of Lone Pairs

Effect on Geometry

• Lone pairs also count as electron domains.

• Example: Ammonia (NH3)

  • Nitrogen has 3 bonds and 1 lone pair, sp3 hybridization.
  • Trigonal pyramidal molecular geometry.

• Example: Water (H2O)

  • Oxygen has 2 bonds and 2 lone pairs, sp3 hybridization.
  • Bent molecular geometry due to lone pair influence.

Summary

• Electron domains (covalent bonds + lone pairs) determine hybridization.

• Hybridization determines electron domain geometry.
• Molecular geometry can vary depending on presence of lone pairs.
• First step in identifying geometry: Draw Lewis dot structure and count electron domains.

Additional Resources

• Subscribe to Professor Dave's channel for more tutorials.
• Contact: professordaveexplains@gmail.com