Shapes of Molecules

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  • Created by: Xynoss
  • Created on: 14-11-13 19:12

Linear Molecules

(c) doc b (http://www.docbrown.info/page04/4_72bond/Image522.gif)

  • Two bonding pairs of electrons or two double bond pairs
  • Linear shape
  • Bond angle 180o
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Bent or V shaped Molecules

(c) doc b (http://www.docbrown.info/page06/ELmcTEST/sh06.gif)    or    (c) doc b (http://www.docbrown.info/page06/ELmcTEST/ox04.gif)

  • Two bond pairs, one lone pair of electrons 
  • BENT or V shape
  • Bond angle approximately 120o
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Trigonal Planar

  • (c) doc b (http://www.docbrown.info/page06/ELmcTEST/sh08.gif) or (c) doc b (http://www.docbrown.info/page06/ELmcTEST/ox11.gif)
  • 3 electron bond pairs
  • TRIGONAL PLANAR:
  • Q-X-Q bond angle exactly 120o
  • e.g. X = B and Q = H for gaseous boron hydride BH3
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Bent or V shaped Molecules (more than 1 non Bondin

(c) doc b (http://www.docbrown.info/page06/ELmcTEST/sh01.gif)

  • Two bond pairs and two lone pairs of Electrons
  • BENT shape
  • e.g. hydrogen sulphide, H2S, or water H2O, 
  • i.e. H2X with H-X-H bond angle of approximately 109o (actually 104.5o in water) 
  • lone pair-lone pair > lone pair-bond pair > bond pair-bond pair.
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PYRAMIDAL or TRIGONAL PYRAMID

  • (c) doc b (http://www.docbrown.info/page06/ELmcTEST/sh02.gif) or(c) doc b (http://www.docbrown.info/page06/ELmcTEST/ox03.gif) 
  • Three bond pairs and one lone pair of electrons 
  • PYRAMIDAL or TRIGONAL PYRAMID shape
  •  e.g. ammonia NH3 with bond angle of approximately 109o
  • Why isn't the H-N-H angle 109o? The exact H-N-H angle is 107o due to the extra repulsion of one lone pair.
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TETRAHEDRAL Shape

(c) doc b (http://www.docbrown.info/page06/ELmcTEST/sh09.gif) or (c) doc b (http://www.docbrown.info/page06/ELmcTEST/ox08.gif)

  • 4 bond pairs of electrons
  • TETRAHEDRAL shape
  • e.g. methane CH4, silicon hydride SiH4 with H-X-H bond angle of 109o and similarly ions like the ammonium ion NH4+.
  • No lone pair, no extra repulsion, no reduction in angle, therefore perfect tetrahedral angle (for H-X-H angles:  CH4 > NH3 > H2O, see below).
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TRIGONAL BIPYRAMID

(c) doc b (http://www.docbrown.info/page06/ELmcTEST/XQ5.GIF) or (c) doc b (http://www.docbrown.info/page06/ELmcTEST/XQ5ox.GIF)

  • 5 bond pairs of electrons
  • TRIGONAL BIPYRAMID shape
  • e.g. phosphorus(V) fluoride (phosphorus pentafluoride) PF5, gaseous phosphorus(V) chloride, PCl5
  • Bond angles 90o and 180based on the vertical Q-X-Q bond and 120o based on the central trigonal planar arrangement.
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OCTAHEDRAL SHAPE

(c) doc b (http://www.docbrown.info/page06/ELmcTEST/XQ6.GIF) or (c) doc b (http://www.docbrown.info/page06/ELmcTEST/XQ6ox.GIF)

  • 6 bond pairs of electrons
  • OCTAHEDRAL SHAPE 
  • e.g. sulfur(VI) fluoride (sulphur hexafluoride moleculeSF6 or the [PCl6]- ion and many transition metal complexes
  • Q-X-Q bond angles of 90o and 180o.(Q TO Q)
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