VSEPR Theory Notes

VSEPR Theory helps predict the shapes of molecules based on electron domains around a central atom. Each bond and lone pair contributes to an "electron domain." Here's how it works:

• Electron Domains: Areas of electron density categorized as:

  • Bonding Domains: Shared electrons (single, double, triple bonds).

  • Lone Pairs: Non-bonding electrons on the central atom.

• Repulsion Order: Lone pairs repel more than bonding pairs:

  • Lone pair–lone pair > Lone pair–bonding pair > Bonding pair–bonding pair.

• Common Geometries:

  • Linear (2 domains, 0 lone pairs): ~180° (e.g., CO₂)

  • Trigonal planar (3 domains, 0 lone pairs): ~120° (e.g., BF₃)

  • Bent (3 domains, 1 lone pair): ~118° (e.g., SO₂)

  • Tetrahedral (4 domains, 0 lone pairs): ~109.5° (e.g., CH₄)

  • Trigonal pyramidal (4 domains, 1 lone pair): ~107° (e.g., NH₃)

  • Bent (4 domains, 2 lone pairs): ~104.5° (e.g., H₂O)

• Important Notes:

  • Memorize shapes and angles for IB Chemistry.

  • VSEPR theory may not apply to isoelectronic species and transition metals.