1. Chapter 6 - 4 Intermolecular Forces or IMF (p. 219 – 224)

2. Intermolecular Forces or IMF
Attractive forces between molecules.
Much weaker than chemical bonds within molecules.
a.k.a. van der Waals forces

3. Intermolecular Forces
If there are no attractive forces between molecules, the substance will exist as a gas because an attractive force is required to hold molecules together as liquids and solids.

4. Types of Intermolecular Forces
London Force (Dispersion forces)
forms when any atom or molecule becomes a dipole at an instant when its electrons are unequally distributed around the nucleus or nuclei.
more electrons, stronger London force

5. Types of IMF
London Dispersion Forces
View animation online.

6. Types of Intermolecular Forces
2. Dipole Force
forms when the positive end of one polar molecule attracts the negative end of another polar molecule.
slightly stronger than London forces.
H F
d+ d-
H F
d+ d-

7. Types of IMF
Dipole-Dipole Forces + -
View animation online.

8. Dipole Interactions
d+ d-
d+ d-
d+ d-
d+ d-
d+ d-
d+ d-
d+ d-
d+ d-

9. Types of Intermolecular Forces
3. Hydrogen bond
forms when a hydrogen atom bonded to a small strongly electronegative atom such as F, O, and N is attracted to another electron-rich atom
the hydrogen is left very electron deficient
the strongest of the intermolecular forces.

10. Types of IMF
Hydrogen Bonding

11. Hydrogen Bonding H O d+ d- H O d+ d-

12. Hydrogen bonding H O H O H O H O H O H O H O

13. Types of IMF

14. Determining IMF CH4 nonpolar = London NCl3
polar = London, dipole-dipole HF
H-F bond = London, hydrogen bonding