Introduction to Vesper Theory

Vesper Theory Basics:

• Vesper theory is used to determine the 3D shape of a molecule from its 2D Lewis structure.
• Recognizes that molecules are three-dimensional.
• Vesper stands for Valence Shell Electron Pair Repulsion.
• Key concept: Electron pairs repel each other and prefer to be as far apart as possible.

Examples and Shapes:

1. Example: Beryllium Dichloride (BeCl₂):

• Structure: Beryllium (central atom) with two chlorine atoms.
• Beryllium is an exception to the octet rule; happy with fewer than eight electrons.
• Shape: Linear.
  • Bond angle: 180°.
• Applies to structures with 2 bonds (e.g., CO₂, HCN).

2. Example: Boron Trifluoride (BF₃):

• Structure: Boron (central atom) with three fluorine atoms.
• Boron also an octet rule exception.
• Shape: Trigonal Planar.
  • Bond angles: 120°.
• Applies to structures with 3 bonds (e.g., CH₂O).

3. Example: Sulfur Dioxide (SO₂):

• Structure: Sulfur with two oxygen atoms and one lone electron pair.
• Shape: Bent.
  • Bond angles: Slightly less than 120° due to lone pair repulsion.

4. Example: Methane (CH₄):

• Structure: Carbon with four hydrogen atoms.
• Shape: Tetrahedral.
  • Bond angles: 109.5°.
• Applies to structures with 4 bonds.

5. Example: Ammonia (NH₃):

• Structure: Nitrogen with three hydrogen atoms and one lone electron pair.
• Shape: Trigonal Pyramidal.
  • Bond angles: 107° (less than 109.5° due to lone pair).

6. Example: Water (H₂O):

• Structure: Oxygen with two hydrogen atoms and two lone electron pairs.
• Shape: Bent.
  • Bond angles: 105° (less than 107° due to two lone pairs).

Key Points to Remember:

• Lone electron pairs exert more repulsion than bonded atoms, affecting bond angles.
• Different numbers of atoms or lone pairs around a central atom result in distinct shapes (linear, trigonal planar, tetrahedral, trigonal pyramidal, bent).

Advanced Topics:

• Videos cover molecules with 5 or 6 things around a central atom:
  • Trigonal Bipyramidal Family: 5 things around central atom.
  • Octahedral Family: 6 things around central atom.

Next Steps:

• Watch Vesper practice problems video to apply concepts.
• Review Vesper common mistakes video to avoid common errors.
• Explore advanced videos on trigonal bipyramidal and octahedral structures if required.