Shapes of Molecules (VSEPR)

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  • Created by: ava.scott
  • Created on: 13-04-14 13:35

Shape Theory

Shape is determined by repulsion between electron pairs.

  • lone pair/lone pair repulsion has the strongest repulsion
  • lone pair/bonded pair has the second strongest repulsion
  • bonded pair/ bonded pair has the least repulsion
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Linear Molecules

e.g. BF2

2 bonded pairs, 0 lone pairs. Bond angle of 180 degrees.

(http://users.stlcc.edu/gkrishnan/vspr2.gif) 

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Trigonal Planar

e.g. BF3

3 bonded pairs, 0 lone pairs. Bond angle of 120 degrees.

(http://users.stlcc.edu/gkrishnan/vspr3.gif)

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Tetrahedral

4 bonded pairs, 0 lone pairs. Bong angles of 109.5 degrees.e.g. CH4 

(http://users.stlcc.edu/gkrishnan/vspr4.gif)

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Octahedral

6 bonded pairs, 0 lone pairs. Bond angles of 90 degrees.e.g. SF6

(http://users.stlcc.edu/gkrishnan/vspr6.gif)

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Bent/ V-shaped

e.g. H2O. 2 bonded pairs, and 1 or more lone pairs. Polar, because the lone pair= negative.

Lone pairs remove 2.5 degrees of a bond angle.(H2O = tetrahedral 109.5 minus 2 x 2.5 degrees= 104.5 degrees)

(http://2.bp.blogspot.com/-cuUD-fDSpVQ/T8EQVI9gf2I/AAAAAAAAAC0/nw7AMK4Il-E/s1600/Wissen9.jpg)

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Trigonal Pyramidal

e.g. NH3

3 bonded pairs, 1 lone pair. Polar, because lone pair= negative.

The lone pair repels the bonded pairs down towards eachother. Bong angles 107 degree (like tetrahedral 109.5 minus 2.5 degrees)

(http://chemlabs.uoregon.edu/GeneralResources/models/grf/NH3.gif)

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