1. Chapter 9 Chemical Bonding
Section 9.2 Molecular Shape and Polarity

2. The Shapes of Molecules
The shape of a molecule and the polarity of its bonds determine whether the molecule as a whole is polar.
The shape is important in predicting properties and how the molecule reacts with other molecules

3. The Shapes of Molecules
Models help us visualize the 3D structures of molecules.

4. Lewis Dot Structure
Review groups – what is the number we want? Draw the Lewis dot structures of the following: CH4 NH3 CO2 H2CO

5. Double Bond- a bond formed by sharing two pairs of electrons between two atoms
Triple Bond- a bond formed by sharing three pairs of electrons between two atoms

6. Shapes
Linear
Trigonal Planar
Bent
Tetrahedral
Trigonal Pyramidal

8. Linear Shape (2 electron groups)

9. Trigonal Shape (3 electron groups)
Trigonal Planar Bent

10. Tetrahedral (4 electron groups)
Bent
Trigonal Pyramid

11. Lone pair electrons Distort the shape of molecules
Example: Tetrahedral geometry
No lone pairs One lone pair Two lone pairs
CH NH H2O

12. Steps in Creating a 3-D model
Draw Lewis structure
Count the # of bonds and lone pair electrons on the central atom
Select geometric category
Place electrons and atoms that lead to most stable arrangement ( minimize e-repulsions)
Determine 3-D

13. Some Models
Create the following models (pg 323) HCl CH4 NH3 H2O C2H6

14. Polar and Non-Polar Molecules
Polarity is important, just like shape, in affecting the properties of compounds. They act TOGETHER.

15. Polar and Non-Polar
Polar molecule – MOLECULE has a positive and negative pole. (Different ENs) - Dipole Non-polar molecule– MOLECULE share electrons equally. (Same ENs)

19. Build the model and predict the polarity of the following:
CCl4
NH3 HF
C2H4