1. Intermolecular Attractions
Chemical BONDING
Intermolecular Attractions

2. Intermolecular attractions
Attractions between molecules
1. London Dispersion Forces
Weak attractive forces between non-polar molecules
Ex. CH4, CO2 & Halogen molecules
Strongest LDF between molecules with LOTS of electrons.

3. Rank in order of weak to strong L-D
F2, I2, Br2, Cl2
H2, CH4, CCl4
I2, CF4, CO2

4. 2. Dipole-dipole attractions
Stronger attractions that occur between polar molecules (still only 1% of the strength of a covalent bond)
Hydrogen “Bonding”
Special type of dipole-dipole force found ONLY between
FH F
OH O
NH N

5. Why does H “bonding” occur with only these 3 atoms?
Nitrogen, Oxygen and Fluorine
3 highest electronegativities
smallest atoms with strongest nuclear charges

6. H “bond”
H F

7. Intermolecular forces determine the properties (behavior) of the substance
Stronger IMFs, result in higher boiling points, higher melting points and slower evaporation of substances.

8. The Unusual Properties of Water
Unusually high boiling point compared to other Hydride compounds in Group 16.
Explain why.

9. Rank these substances from highest to lowest boiling point
NaCl I2
H2O H2
H2S

10. H2O Hydrogen bonding IMF
NaCl Ionic bonding
H2O Hydrogen bonding IMF
H2S dipole-dipole IMF not as strong as H bonds
I2 stronger LDF larger e- cloud than H2
H2 weakest LDF smallest e- cloud
Lowest Highest

11. The End