https://www.youtube.com/watch?v=keHSCASZfc&feature=related
Valence Shell Electron Pair
Repulsion Theory (VSEPR Theory):
Looking at molecules in 3D!!!
Friday, January 8th, 2016
Molecular Shape
VSEPR theory assumes that the shape of a
molecule is determined by the repulsion of
electron pairs.
VSEPR Theory
• Based on Electron Dot (Lewis structures)
• VSEPR Theory predicts shapes of compounds
• VSEPR (pronounced “vesper”) stands for Valence
Shell Electron Pair Repulsion
• VSEPR predicts shapes based on electron pairs
repelling (in bonds or by themselves)
• Electrons around central nucleus
repel each other. So, structures
have atoms maximally spread out
VSEPR overview
• Each shape has a name (you should know these 5)
• Names of Shapes:
• tetrahedral
• trigonal pyramidal
• Bent
• Linear
• trigonal planar
Tetrahedral
Triangular Planar
Trigonal pyramidal
Bent
Linear
Example 1: Methane (CH4)
Example 2: Ammonia (NH3)
Example 3: Water(H2O)
methane, CH4
Tetrahedral
109.5°
Bonds are all evenly spaced electrons
..
..
..
..
ammonia
NH3
Trigonal Pyramidal
Less repulsion between the bonding pairs of electrons
..
..
..
water, H2O
109.5° (109.5°) 109.5° (107°)
109.5° (104.5°)
..
..
..
Bent or V
2 unshared pairs of e’s
at top of O repel bonds
and force them to bend
Steps to Success
1. Draw the Lewis Structure for each atom
- Count up the valence electrons, determine central atom, bond
terminal atoms, recount, add lone electron pairs, check & shift to share if
necessary
2. Determine VSEPR Structure
-- # atoms bound
-- # unpaired electrons on central atom
3. Redraw as VSEPR Structure
Example 4: Carbon Dioxide (CO2)
Example 4: Carbon Dioxide (CO2)
Molecule Kit Lab Activity
• With your partner, you will draw the lewis dot structures for
several compounds.
• You will construct the compounds from the kits provided
and sketch your models.
• Identify the molecular geometry (shape) of your compound
from the central atom and label the bond angles.
• Lastly, determine if you compound is polar or nonpolar
(horse & cart)