Lecture #16
 
  CURMUDGEON GENERAL'S WARNING. These "slides" represent highlights from lecture and are neither complete nor meant to replace lecture. It is advised not to use these as a reliable means to replace missed lecture material. Do so at risk to healthy academic performance in 09-105.
Lecture Outline Molecular Geometries

VSEPR Model

Distortions from ideal geometries

effect of lone pairs vs bonding pairs

effect of multiple bonds

effect of lone single electrons
The relative effectiveness of different electron pair repulsion combinations. The example illustrated shows how the HOH bond angle is distorted down to 104.5o from its ideal tetrahedral angle of 109.5o
An illustration of how the differences between electron pair repulsions leading to the preferred see-saw geometry of a molecule of type AB4E.
Further distortions from the ideal VSEPR geometry of a molecule of type AB4E.
Here is the rationale behind choosing the T-shaped molecular geometry for two lone pairs and three bonding pairs about a central atom. (This was not done in lecture). Two of the choices have six unfavorable repulsions at 90o. The other has only four such repulsions. See it?
Illustrating the imbalance when SF4's lone pairs distort bond angles and bond lengths from the ideal VSEPR geomtry.
In a molecule of type AB4E2, the lone pair repulsions make the preferred molecular geometry that corresponding to square planar. This gives minimum lone pair-lone pair repulsions
The molecular geometry of structure AB5E and the distortions from the ideal square pyramidal molecular geometry caused by the lone pair of electrons.
Additional considerations that lead to distortions from ideal VSEPR molecular geometries. (These are not in the textbook.)
Effect of multiple bonds.
Illustration of double bond effect in POCl3
The effect of a lone single electron.
Illustrating the lone electron effect by comparing ClO2- to ClO2