VSEPR Theory postulates and geometry.ppt

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1. VVALENCEALENCE
SSHELLHELL
EELECTRONLECTRON
PPAIRAIR
RREPULSIONEPULSION
THEORYTHEORY
Planar triangular
Tetrahedral
Trigonal
bipyramidal
Octahedral

2. Essential Question
•How is VSEPR Theory used to determine
molecular geometry?

3. What is VSEPR Theory?
•Valence Shell Electron Pair Repulsion
Theory
•Predicts molecular geometry (shape)
•Only works for:
•Covalent compounds & polyatomic ions
•Compounds with central atom

4. Shape Depends On:
•e
-
on central atom only
•# of lone pairs
•# of bonded atoms
•Single, double, & triple bonds have the same
effect (count as one bond)
Atoms
bonded
Lone pair of electrons
2 bonded atoms, no lone
pairs: linear
Double bonds still count
as one bonded atom

5. Steps to Determine Shape
1.Draw Lewis Dot Structure
2.Count # of lone pairs on central atom
3.Count # of bonded atoms on central atom
4.Determine shape using the VSEPR
Shape Chart

6. 5 Types of Shapes
•The shape of a molecule can be categorized into 5
general shapes.
•1. Linear
•2. Trigonal Planar
•3. Tetrahedral
•4. Trigonal Bipyramidal
•5. Octahedral
•The geometrical shape is the arrangement of the atoms around a
central atom based on the number of atoms, and the amount of
lone pairs, which contribute to the overall shape.

7. •To represent a 3-D structure on a two dimensional surface, we use solid
lines, dashed lines, and wedges, as seen below.
Line= in the plane of the board
Wedge= coming out of the board
Dashes= going into the board