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Molecular Shapes

Chemistry: IB Diploma Higher Level, topic 2.7.2

Electron Pairs and Geometry

There is an optimal geometry for every number of electron pairs. The different types of geometry are:

Linear

Linear

  • If the central atom of a molecule has two electron pairs, it will likely adopt a linear geometry.
  • The bond angle will be 180o.
Trigonal planar

Trigonal planar

  • If the central atom of a molecule has three electron pairs, it will likely adopt a trigonal planar geometry.
  • The bond angle will be 120o.
Tetrahedral

Tetrahedral

  • If the central atom of a molecule has four electron pairs, it will likely adopt a tetrahedral geometry.
  • The bond angle will be 109.5o.
Trigonal bipyramidal

Trigonal bipyramidal

  • If the central atom of a molecule has five electron pairs, it will likely adopt a trigonal bipyramidal geometry.
  • Molecules with this shape have two bond angles:
  • A 120o angle around the equator.
  • A 90o angle from equator to apex.
Octahedral

Octahedral

  • If the central atom of a molecule has six electron pairs, it will likely adopt an octahedral geometry.
  • The bond angle will be 90o.

Test yourself on Molecular Shapes

  • A molecule has four electron pairs around its central atom. What will its geometry be?

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