The Valence-Shell Electron-Pair Repulsion (VSEPR) Model

At the start of class Mrs. Mandarino stamped the homework pages 18 &19.

Then we reviewed Molecular Geometry, and we started on Molecular Geometry lab.


Molecular geometry is the three dimensional arrangement of the atoms that constitute a molecule. It determines several properites of a substance.

The Valence-Shell Electron-Pair Repulsion (VSEPR) Model

There are basic shape types for molecules.


Linear: In a linear model, atoms are connected in a straight line. The bond angles are set at 180 degree.

Trigonal plannar: The trigonal planar shape are somewhat triangular and in one plane. The bond angles are set at 120 degree.

Tetrahedral: "Tetra" means 4. This is when there are four bonds all on one central atom, with NO extra unshared electron pairs. The bond angles between the electron bonds are set at 109.5 degree.

Trigonal Pyramidal: Pyramidal-shaped molecules have pyramid-like shapes. Requires three dimension in order to fully separate the electrons. The bond angles are set at 107 degree.

Bent: The final basic shape of a molecule is the non-linear shape, also known as bent or angular.


Trigonal Planar: 115 degree


Trigonal Pyramid: 105 degree

Electron Pairs on Central Atom

2/2/0 - Linear
3/3/0 -Trigonal Planar

3/2/1

4/4/0- Tetrahedral
4/3/1

4/2/2

Example:

PCl3

4/3/1 - Trigonal Pyramidal

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HW: Tuesday, Nov.16,2010 = Molecular Geometry Lab (questions), Chemthink & Webassign