Vespa Theory and Molecular Geometry

Introduction to Vespa Theory

• Vespa Theory stands for Valence Shell Electron Pair Repulsion.
• Predicts molecular shape based on electron repulsion.
• Electrons repel each other and want to be as far apart as possible.
• Helps in predicting molecular shapes.

Linear Molecular Geometry

• Linear Geometry: Atoms form a straight line.
• Example Molecules:
  • BeCl₂ (Beryllium Chloride): Looks like a straight line.
  • CO₂ (Carbon Dioxide): Another example of a linear molecule.
  • Triiodide Ion (I₃⁻): Consists of three iodide atoms, forming a linear shape.
• Bond Angle: 180 degrees.

Trigonal Planar Structure

• Trigonal Planar: Atom surrounded by three other atoms, flat as paper.
• Example Molecules:
  • BH₃ (Boron Hydride): Boron at the center with three hydrogens.
  • COCl₂: Carbon with a double bond to oxygen and two chlorine atoms.
• Bond Angle: 120 degrees (360 divided by 3).

Tetrahedral Molecular Structure

• Tetrahedral Structure: Atom surrounded by four other atoms.
• Example Molecules:
  • CH₄ (Methane): Carbon with four hydrogen atoms.
  • SiF₄ (Silicon Tetrafluoride): Silicon with four fluorine atoms.
• Bond Angle: Approximately 109.5 degrees.

Trigonal Pyramidal Structure

• Trigonal Pyramidal: Central atom with a lone pair surrounded by three atoms.
• Example Molecules:
  • NH₃ (Ammonia): Nitrogen with a lone pair and three hydrogen atoms.
  • PH₃ (Phosphine): Phosphorus with three hydrogen atoms.
• Bond Angle: Approximately 107 degrees.

Bent Molecular Geometry

• Bent Geometry: Central atom with lone pairs bending the structure.
• Example Molecules:
  • H₂O (Water): Oxygen with two lone pairs.
  • SO₂ (Sulfur Dioxide): Sulfur with one lone pair and two oxygen atoms.
• Bond Angles:
  • Water: 104.5 degrees.
  • Sulfur Dioxide: Less than 120 degrees.

Summary of Molecular Structures

• Tetrahedral (CH₄): 109.5 degrees.
• Trigonal Pyramidal (NH₃): 107 degrees - similar to tetrahedral but with a lone pair.
• Bent (H₂O): 104.5 degrees - similar to tetrahedral with two lone pairs.
• Trigonal Planar (BH₃): 120 degrees.
• Similar to BH₃, SO₂: Close to 120 degrees but slightly less due to lone pair influence.