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SolutionsMolecular Geometry

1. Predict the geometry

Predict the shape of each molecule from the electron pairs around the central atom:

  1. CH4
  2. NH3
  3. H2O
  4. BF3
  5. CO2
  1. Tetrahedral: four bonding pairs.
  2. Pyramidal: three bonding pairs and one unshared pair.
  3. Angular: two bonding pairs and two unshared pairs.
  4. Trigonal planar: three bonding pairs.
  5. Linear: two electron densities (two C=O double bonds).

2. Angles

The H–O–H angle of water (104.5°) is smaller than the tetrahedral angle of methane (109.5°). Why?

The unshared pairs of oxygen take up more space than the bonding pairs (only one nucleus attracts them) and push the two O–H bonds, which close up slightly.

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