1. Polar or Non-Polar
That is the question…

2. Review: Bond Polarity
What do we mean when we say a bond between two atoms is polar? Non-polar?
Non-polar: Electronegativity difference = 0
Electrons are shared equally
Polar: Electronegativity difference > 0
One atom pulls electrons toward it more

3. Molecule Polarity Bond Polarity leads to Molecule Polarity
H2 vs. HF - draw vector arrows
- can you separate + and -?
Non-polar bond, Polar bond
Non-polar molecule Polar molecule

4. What if the molecule is more complicated?
Examples: BF3 and CH4
To determine polarity, you must first know 3D shape.
Then, draw vector arrows for each bond.
Ask yourself, can I separate + and - with a straight line?
Polar bonds BUT
Molecules are Non-polar
overall.

5. What if the molecule has lone pairs?
Lone pairs are negative!
Draw arrows for each bond and lone pair.
Can you separate + from - ?
Polar bonds
Polar molecules

6. Polar or Non-Polar? SiF4 Non-polar molecule, polar bonds AlCl3 H2S
Non-polar molecule, non-polar bond
CS2
CBr4
PH3

7. Summary So… It is possible for molecules to have:
Non-polar bonds and be non-polar overall
Polar bonds and be non-polar overall
Polar bonds and be polar overall
Can there be molecules with non-polar bonds that are polar overall?

8. Intermolecular Forces
Intra vs. Inter
Attractions within a molecule (Intra) vs. Attractions between molecules (Inter).
Not as strong as chemical bonds.
Also play a role in macroscopic properties we can observe.

9. Dipole-Dipole Force Dipole = two poles or POLAR
attraction between two or more polar molecules
most common IMF
oppositely charged sides of molecules attracting each other

10. Dipole-Dipole Cont’d Hydrogen bonding –
type of dipole-dipole IMF
Special, stronger dipole attraction
Made of a H of one molecule and F,O, or N of another molecule
Primary ex. – H2O, HF, NH3
“Chemistry is FON”
Causes intermolecular
attraction to be stronger than predicted –
raises b. pt. higher than predicted

11. Hydrogen Bonding

12. Remember this?
Plateaus are where IMFs are broken.

13. Ice… it floats!

14. It’s in your DNA…

15. Dipole-Dipole Forces
Ethanol and Water - demo

16. What about non-polar molecules?
Van der Waals forces OR London dispersion forces
*Caused by momentary dipole attraction*
Weakest intermolecular attraction
lowest m. pt., b. pt., insoluble, nonconductors
Allow gases to become liquids or solids under conditions of low temperature and high pressure
Strength affected by:
number of electrons,
mass of molecule,
distance between the molecules
Only form of attraction
between the noble gases

17. How does it work?
Momentary Dipoles
are formed.
They attract other
molecules.

19. Dry Ice Solid CO2 Sublimation

20. Molecule-Ion Attraction
Attraction between ions and molecules
Most common when ionic solids dissolve in water
(+) ion will be attracted by negative side of water molecules and
(-) ion will be surrounded by the positive side of water molecule
Allows for electrical conductivity of solutions – mobile ions: increase number of ions, increase conductivity

21. Solutions of ionic
compounds
Video