Intermolecular Forces

1. Intermolecular Forces

2. Solids, Liquids, and Gases

4. Intermolecular Attractions

5. Intermolecular Vs Intramolecular forces • Intermolecular forces are much weaker than intramolecular forces. • Example: • We need about 41kJ to vaporize 1 mole of water at its boiling point (to overcome intermolecular forces), but about 930 kJ are needed to break the two O-H bonds.

6. Ion – Dipole interaction

8. Dipole – Dipole Interaction

10. London Dispersion Forces(instantaneous dipoles)

11. Polarizability: the ease with which the electron distribution around an atom or molecule can be distorted.Dispersion forces increases with: 1. polarizability2. atomic or molecular mass3. number of electrons

12. Van der Waals Forces • Dipole – dipole forces • Dipole – induced dipole forces • Dispersion forces (London forces) • But not ion-dipole forces or hydrogen bonding

14. Example: Correlate intermolecular forces to mp

15. Which is greater: dipole dipole or dispersion forces? • CH3F has a dipole moment of 1.8 Debye, while CCl4 has no dipole moment. The boiling point of the two compounds are -78.4 and 76.5 oC. Although CH3F has both dipole – dipole forces and dispersion forces, it has a much lower BP (smaller intramolecular forces) than CCl4 which has dispersion forces only. However this is not always true.

18. Example: What types of intermolecular forces exists between the following pairs: • a. HBr and H2S • Cl2 and CBr4 • I2 and NO3- • NH3 and C6H6 • CH3Cl and CCl4 • KBr and H2O

20. Hydrogen Bonding

21. A hydrogen bond can form when: • We have molecules containing one of the following groups: • N-H • O-H • H-F • And O, N, or F atoms in the same molecule or other molecules

25. Density of water

27. Highest density occurs at 4oC. • From 0 – 4oC, trapping prevails which results in an increase in density • Above 4oC, thermal expansion predominates resulting in a decrease in density