Today in class we continued learning about polarity and nonpolarity

• MOLECULAR AND INTERMOLECULAR BONDS
Intermolecular means the bonds outside molecules
- Intramolecular means bonds inside molecules

• Polarity is the result of intermolecular bonds
• Most bonds are electrostatic:

1. LONDON DISPURSION FORCE (L.D.F)
- Experienced by all molecules
- Result of electrons pushing on each other
- Weakest of all forces

- As the number of electrons increase L.D.F increases

- Comparison between the atoms Aluminum and Argon
Q:Which molecule will have a longer l.d.f?
A: Argon because it’s got more electrons. Which ever has more electrons experiences a longer LDF
- As the number of electrons increase L.D.F increases.



2. Dipole- Dipole
- Dipoles are partial separation of charges
- L.D.F is a type of temporary dipole
- Why is it a temporary dipole? Because electrons are always moving. Electrons always moving they don’t necessarily have to be in the same place.
- Some molecules have a permanent dipole
- These are polar molecules
- Polarity is determined by electrons affinity (how much an atom wants electrons)
- Electrons affinity is called electronegativity
- Electronegativity is highest on the top right and lowest on the bottom left


- Electronegativity is highest on the top right and lowest on the bottom left.
- A bond between two atoms/molecules with different electronegativities results in a dipole-dipole bond.

• Whats a dipole dipole strength between the two molecules Cl -Cl? None! Because none of them are polar
• Polar= dipole dipole
EXAMPLES: which bonds will result in a dipole-dipole force?

1.H-Clyes
2. O-Hyes
3. F-F No
4. O-Cl yes
5. I-Br yes

Are the following compounds polar or nonpolar?
1. CHCl3polar
2. 2. BI2Brpolar
3. C2H4non polar
4. C2H2Cl2non polar

DIPOLE DIPOLE FORCES ARE WEAK VERSIONS OF IONIC BONDS
COMPOUND Boiling Point Number of electrons
N2 -196 degrees celcius 14
O2 -183 16
NO -152 15
ICL 97 70
Br2 59 70

homework: questions 1 & 2 on worksheet