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Understanding SP2 Hybridization and Geometry

Aug 14, 2024

Lecture Notes: SP2 Hybridization and Molecular Geometry

Overview

  • SP3 hybridization (tetrahedral geometry) vs. SP2 hybridization (planar geometry)
  • Importance of hybridization in understanding molecular structures

Ethylene (C2H4) Hybridization

Geometry and Hybridization

  • Carbon in ethylene is bonded to three atoms (H, H, C) with planar geometry
  • Bond Angles: Approximately 120 degrees
  • Hybridization: SP2 (one S orbital + two P orbitals)
    • Results in three SP2 hybrid orbitals and one unhybridized P orbital

Electron Configuration

  • Electron Promotion: Promote S orbital
  • SP2 Hybrid Orbitals:
    • 33% S character
    • 67% P character
  • Effect on Bond Length: Increased S character brings electron density closer to nucleus, shortening bond length

Molecular Structure

  • SP2 Orbital Shape: Larger front lobe, smaller back lobe
  • Sigma Bonds: 5 total in ethylene
    • Head-on overlap of orbitals
  • Pi Bonds: Side-by-side overlap of unhybridized P orbitals
    • Prevents free rotation
    • Presence of one pi bond in ethylene
  • Bond Length: 1.34 Å (shorter than ethane)

Steric Number Concept

  • Steric Number: Sigma bonds + lone pairs
  • Example: Ethylene carbon
    • 3 sigma bonds, 0 lone pairs → Steric number = 3
    • Confirms SP2 hybridization

Boron Trifluoride (BF3) Example

Hybridization

  • Boron in BF3 shows SP2 hybridization
  • Steric Number: 3 sigma bonds, 0 lone pairs → Steric number = 3

Electron Configuration

  • Boron has 3 valence electrons (unlike carbon’s 4)
  • SP2 Hybrid Orbitals: Boron has three SP2 hybrid orbitals, one unhybridized P orbital
    • No electrons in unhybridized P orbital

Chemical Behavior

  • Lewis Acidity: Boron can accept electron pairs
  • Geometry: Planar with 120-degree bond angles

Conclusion

  • SP2 hybridization leads to planar geometry and specific bonding characteristics
  • Next topic: SP hybridization

These notes summarize key concepts related to SP2 hybridization and its effects on molecular geometry and bond characteristics, using ethylene and boron trifluoride as examples. The discussion highlights the relationship between hybridization, electron configuration, and molecular behavior.

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