Chapter 9: Molecular Geometry and Bonding Theories

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Chapter 9 Molecular Geometry and Bonding Theories

• What do the molecules look like and why?

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Valence Shell Electron Pair Repulsion Theory
(VSEPR)

• VESPR is a model of how molecules arrange
  themselves and get their shape.
• It is based on the idea that the groups of
  electrons (often called electron domains) around
  the central atom will repel one another to get as
  far away from each other as possible.
• Each non-bonding pair, single bond or multiple
  bond produces an electron domain around the
  central atom.
• There are five possibilities for the arrangement
  of groups of electrons around the central atom.
• 2, 3, 4, 5, and 6 groups of electrons

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Electron Group Geometry

• These geometries are called electron group
  geometries (EGGs) and these are the only
  possibilities for this.

Electron Pairs Around Central Atom Electron Geometry
2 Linear
3 Trigonal planar
4 Tetrahedral
5 Trigonal bipyramidal
6 Octahedral
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Basic Shapes
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Molecular Geometries

• Molecular geometries are the shapes of the
  molecules when we look at the bonding groups of
  electrons.
• The non-bonding groups are the lone pairs and do
  affect the geometry slightly.
• The electron domains for non-bonding electron
  pairs and multiple bonds exert greater repulsive
  forces on adjacent electron domains and therefore
  tend to compress bond angles.
• If there are no lone pairs on the central atom,
  the molecular and electron group geometries are
  the same.

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Bond Angles

• Look back at pictures and models you built and
  discuss with table.

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Hybrid Orbitals

• Hybrid orbitals are different for each electron
  geometry.

Electron Pairs Around Central Atom Electron Geometry Hybrid Orbitals
2 Linear sp
3 Trigonal planar sp2
4 Tetrahedral sp3
5 Trigonal bipyramidal sp3d
6 Octahedral sp3d2