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Electron Domains

The VSEPR (Valence Shell Electron Pair Repulsion) Theory states that molecules will attain whatever shape keeps the valence electrons of the central atom as far apart from one another as possible.

  • Unshared pairs of electrons on the central atom determine the shape.
  • Electron pairs REPEL each other.

 

  • Electron domain: The space occupied by valence electrons in a molecule, either a bonded pair(s) or a lone pair. Electron domains affect the overall shape of a molecule.
  • Electron domain theory: The idea that every electron domain in a molecule is as far as possible from every other electron domain in that molecule.
    • 4 bonding pairs, 0 lone pairs- tetrahedral shape (109.5 degrees)
    • 3 bonding pairs, 1 lone pair- trigonal pyramidal (105 degrees)
    • 2 bonding pairs, 2 lone pairs- bent
    • 2 bonding pairs (double bonds), 0 lone pairs- linear (180 degrees)
      • Lone pairs occupy more space than bonding electron pairs.

      • Double bonds occupy more space than single bonds.

Polarity

  • Static electricity
    • When two different materials are rubbed together, some electrons can transfer
      • This results in an imbalance of positive and negative charges
  • Partial charges at different locations on a molecule cause a polar molecule
    • Polar molecules are attracted to each other
  • Polar Molecules: Molecules that are attracted to a charge because they have partial charges on them; one side is slightly negative and the other side is slightly positive
  • Non-Polar Molecules: Molecules that are not attracted to a charge

 

  • Attractive molecules
    • Partial Charges- molecules don’t share their electrons equally
      • Polar molecules; have a dipole moment
    • Non-polar molecules- share their electrons equally; have no charge
      • 2 polar bonds may cancel out if they are going in opposite directions
    • Intermolecular Forces- Attraction between molecules (not within)
      • Forces that hold liquids and solids together
        • When a substance melts or boils intermolecular forces are broken
        • When a substance condenses or freezes, intermolecular forces are formed