1. Intermolecular forces

2. Intermolecular Forces
Forces that occur between molecules.
Intramolecular (ionic and covalent) bonds are stronger than intermolecular forces.

3. Intermolecular Forces
There are four kinds of intermolecular forces.
Dipole–dipole forces (between polar molecules)
Hydrogen bonding (between H of one polar molecule and O, N, F of another polar molecule)
Ion-Dipole Forces (between ions and molecules)
London dispersion forces (between nonpolar molecules)

4. Dipole–Dipole Attraction
Polar molecules contain different atoms which have different electronegativities.
Oppositely charged ends attract and like ends repel.
Molecules organize themselves maximizing the attractive forces and minimize repulsive forces

5. Hydrogen Bonding Strong dipole-dipole forces.
Hydrogen is bound to a highly electronegative atom – nitrogen, oxygen, or fluorine.
Blue dotted lines are the intermolecular forces between the water molecules.

6. Hydrogen Bonding
Affects physical properties
Boiling point

7. London Dispersion Forces
Instantaneous dipole in a given atom induces a similar dipole in a neighboring atom.
Significant in large atoms/molecules.
Occurs in all molecules, including nonpolar ones.

8. Ion Dipole Forces
They are typically found in aqueous solutions of ionic compounds (salt water)
Nonbonding electrons found on the oxygen atom are strongly attracted to the sodium ion.

9. Overview of intermolecular Forces
Type of Force Relative Strength Present in Examples
Dispersion Force
(London Force)
Weak, increasing with size
atoms/molecules
H2 (g)
Polar molecules
HCl
Dipole-dipole force
moderate
Molecules with hydrogen bonded to N,O, or F
Hydrogen bond
Strong
HF, NH3, H2O
Ion-dipole
Very strong
Mixtures of ionic and polar compounds
Na+,Cl-, and H2O