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electron geomtry vs. molecular geometry

Discussion in 'MCAT Discussions' started by badasshairday, Apr 28, 2007.

  1. badasshairday

    badasshairday Vascular and Interventional Radiology 10+ Year Member

    Apr 6, 2007
    Sorry if this is a dumb question, but what the hell is the difference?

    What is the difference between trigonal pyramidal and tetrahedral?
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  3. SpartanBlueJay2

    SpartanBlueJay2 5+ Year Member

    Mar 15, 2007
    All you chem geniuses out there, correct me if I'm wrong, but here's my 2 second explanation:

    Both trigonal pyramidal and tetrahedral are sp3 hybridized, but differ in the number of atoms attached to the central atom. For example, methane and ammonia are both sp3, but methane has 4 H atoms attached to the C, so it is tetrahedral, while ammonia has 3 H atoms attached to the N, so it is trigonal pyramidal.
  4. canjosh

    canjosh 7+ Year Member

    Jun 18, 2004

    NH3 is trigonal pyramidal because of the lone pair. H2O has 2 lone pairs and 2 atoms bonded to the central H atom. H2O's molecular geometry is angular (104.5 degrees). Just remember molecular geometry theory is concerned with only the positions of bonded atoms, not the positions of lone pairs. You still take into account the existence of lone pairs (if that makes sense).

    Electron pair geometry IS concerned with positions of bonded atoms AND positions of lone pairs.

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