1. Intermolecular Forces

2. Intermolecular forces are attractive forces among molecules.
(Example: water molecule to water molecule)
Intramolecular forces hold atoms together within in a molecule.
(Example: H to O bond within a water molecule).
Generally, intermolecular forces are much weaker than intramolecular forces.
“Measure” of intermolecular force
boiling point
melting mpoint
Hvap
Hfus
11.2

3. Intermolecular Forces
1. London Forces (a.k.a. Dispersion Forces) AKA Van Der Waals Forces Weakest
Dipole-Dipole Interactions
Ion-Molecule Interactions
-(Salt dissolving in solution; Na+ and Cl- )
4. Hydrogen Bonding (STRONGEST)

4. London Dispersion (Van Der Waals) Forces Weakest
Occur between nonpolar molecules and arise from the net attractive forces
among molecules which are produced from temporary charge imbalances
The larger the molecule the greater
it’s Dispersion Forces are.

5. Is the Molecule Polar?
The more Electronegative atom will pull the electron density of the bond
Closer to itself giving it a partial negative charge leaving the other
Atom with a partially positive charge. This is a dipole moment.

6. Which of the following molecules are polar (have a
dipole moment)?H2O, CO2, SO2, and CH4 O H S O
dipole moment
polar molecule
dipole moment
polar molecule C H C O
no dipole moment
nonpolar molecule
no dipole moment
nonpolar molecule
10.2

7. Orientation of Polar Molecules in a Solid
Dipole-Dipole Forces
Attractive forces between polar molecules
Orientation of Polar Molecules in a Solid
11.2

8. Ion-Molecule attraction
Attractive forces between an ion and a polar molecule
Ion-Molecule Interaction
The larger the charge the stronger the force
11.2

9. A molecular picture showing the ion-dipole
Olmsted Williams
Fig 10-34
A molecular picture showing the ion-dipole
Interaction that helps a solid ionic crystal dissolve
in water. The arrows indicate ion-dipole interactions.

10. What type(s) of intermolecular forces exist between each of the following molecules?
HBr
HBr is a polar molecule: dipole-dipole forces. There are also dispersion forces between HBr molecules.
CH4
CH4 is nonpolar: dispersion forces.
CO2
CO2 is a nonpolar molecule:Van Der Waals.
11.2

11. The Hydrogen Bond STRONGEST INTERMOLECULAR FORCE

12. water has the highest heat of fusion
water has the highest melting point
water has the highest boiling point
water has the highest heat of vaporization
water has the lowest molar mass
The melting point, boiling point, heat of fusion and heat of vaporization of water are extremely high and do not fit the trend of properties relative to molar mass within Group 16.

13. Water exhibits these unusual properties because of hydrogen bonding between water molecules.

14. A hydrogen bond is an intermolecular force formed between polar molecules that contain hydrogen covalently bonded to a small, highly electronegative atom: F, O, N.
F—H
O—H
N—H

15. The H of one molecule will be attracted to another F, O, or N, on another molecule.
A dipole-dipole bond will be formed between the two molecules which is called a hydrogen bond.
hydrogen bond
covalent bond
covalent bond

16. Water in the liquid and solid states exists as groups in which the water molecules are linked together by hydrogen bonds.
13.8