Molecular Geometry and Hybridization Overview

Oct 7, 2024

Lecture Notes: Molecular Geometry and Hybridization

Introduction to Molecular Geometry

  • Focus on properties of atoms and types of bonds:
    • Covalent bonds: sharing of valence electrons
    • Ionic bonds: complete transfer of electrons
  • Importance of understanding 3D arrangement of molecules
  • Goal: Predict geometry of molecules around a central atom

Lewis Structures

  • Atoms share unpaired electrons for a full octet
  • Representation in 2D using Lewis structures
  • Preferences for covalent bonds:
    • Carbon: 4 bonds
    • Nitrogen: 3 bonds
    • Oxygen: 2 bonds
    • Hydrogen: 1 bond

Determining Molecular Geometry

  • Key information needed:
    1. Number of electron domains (lone pairs or bonds)
    2. Number of bonding electron domains
  • Electron domains determine molecule shape but lone pairs are not part of geometry

Hybrid Orbitals

  • Concept of hybrid orbitals:
    • Used to explain molecular geometry
    • Rearrangement of atomic orbitals into hybrid orbitals
    • Types: sp, sp2, and sp3
  • Hybrid orbital designations:
    • sp: combination of s and one p orbital
    • sp2: combination of s and two p orbitals
    • sp3: combination of s and three p orbitals

Visualizing Geometries

  • sp3 Hybrid Orbitals:
    • 4 electron domains:
      • Tetrahedral: 4 bonding domains, example: Methane (CH4)
      • Trigonal Pyramidal: 3 bonding, 1 lone pair, example: Ammonia (NH3)
      • Bent: 2 bonding, 2 lone pairs, example: Water (H2O)
      • Linear: 1 bonding, example: Hydrogen Fluoride
  • sp2 Hybrid Orbitals:
    • 3 electron domains:
      • Trigonal Planar: 3 bonding domains, example: Borane (BH3)
      • Bent: 2 bonding, 1 lone pair
      • Linear: 1 bonding
    • Double bonds involve sigma and pi bonds, e.g., Formaldehyde
  • sp Hybrid Orbitals:
    • 2 electron domains:
      • Linear: 1 or 2 bonding domains, examples: Nitrogen gas (N2), Acetylene (C2H2)

Molecular Orbital Theory

  • Hybrid orbital theory vs. molecular orbital theory
    • Hybrid: orbitals hybridize before bonding
    • Molecular: uses wave equations to form orbitals from bonded atoms
  • No practical use in lecture but important to be aware of

Summary

  • Understanding molecular geometry requires recognizing electron domains and bonding domains
  • Different hybridization leads to different molecular shapes
  • Use Lewis structures to predict geometries
  • Intro to different bonding theories, emphasizing hybridization in organic chemistry