1. Molecular Geometry & Polarity
A. Substance structure will influence physical properties
• Lewis dot structure for molecules
• Molecular Polarity (polar versus nonpolar)

2. A. Be able to draw
Lewis dot structures
B. molecules have ideal
or non-ideal geometry
C.electronegativity
differences
determines bond polarity
These ideas are described on the next two slides
D. Overall Molecular Geometry
determines molecular polarity

3. Symmetric versus Asymmetric
Symmetrical arrangement
of polar bonds
bond polarities cancel
Asymmetrical arrangement
of polar bonds
bond polarities don’t cancel NO
Net
Dipole
Bond
Dipoles
Cancel
These
Molecules
Have a
Net
Dipole
variable polarity
ammonia
gas
water
polar
non-polar

4. Molecular Substances (discrete units)
Molecular Geometry and Bond Polarity
Ideal geometries show have variable polarity
Non-ideal geometries are generally polar NO
Net
Dipole
Bond
Dipoles
Cancel
ideal non-polar
ammonia
gas
water
polar
These
Molecules
Have a
Net
Dipole
ideal
non-ideal
variable polarity
polar
These
Molecules
Have a
Net
Dipole
BUT, these ideal
geometries here
are polar

5. Draw in bond dipole for each bond

7. Molecular Polarity
Determining the polar nature of molecular substances
Evaluating Substance Structure
Physical Observations - Common Sense Approach
Solubility (solute/solvent interactions) to gauge molecular polarity
“Like will dissolve Like”
Polar solutes will have highest solubility in polar solvents
Nonpolar solutes will have highest solubility in nonpolar solvents
Polar solutes will have lowest solubility in nonpolar solvents
Nonpolar solutes will have lowest solubility in polar solvents

8. Molecular substance solubility in water “Like dissolves Like ” to gauge Molecular Polarity
Sugar dissolves in water
Thus sugar molecules must be polar
Methanol CH3OH dissolves in water
Thus methanol molecules must be polar
Gasoline -(CH 2)- does not dissolve in water
Thus gasoline molecules must be NONPOLAR

9. A gasoline molecule is a hydrocarbon made of
repeating –( CH2 )– units  is non-polar; NO net dipole
hydrocarbons are non-polar
A gasoline hydrocarbon
All dipoles cancel

10. Nonpolar does not dissolve Polar
methane does not dissolve in water
gasoline does not dissolve in water

11. Polar physically dissolves in Polar
opposites attract
physical bonding
methanol dissolves in water
sugar dissolves in water
opposites attract
physical bond

12. The highlighted area is an example of hydrogen bonding
methanol dissolves in water
sugar dissolve in water

13. “Like dissolves Like” Polar dissolves Polar Vitamin B11 (folic acid)
Vitamin C (ascorbic acid)
Where ever there are N and O atoms, there are polar areas
polar areas
Water soluble vitamins

14. “Like dissolves Like” Non-Polar dissolves Non-Polar
Vitamin A, retinol (fat soluble; lipid soluble)
triacylglycerine, a non-polar human body fat (lipid)
nonpolar areas
Vitamins D, E, and K are fat soluble as well
What would their overall polarity be?

15. Predict whether the substance is Polar or Nonpolar
sugar C6H12O6
baby oil C20H42
candle wax C40H82
ethanol C2H5OH
oxygen O2
iodine I2
polar
nonpolar