1. Intermolecular Attractive Forces: Liquids and Solids
Chapter 14
C2 Ch 14 ppt 1 - IMAF's.ppt
C2 Ch 14 ppt 1 - IMAF's.ppt 1 1 1 1

2. In today’s lesson, you will learn:
The different types and relative strengths of intermolecular attractive forces How to apply heat of vaporization and heat of fusion Relationship between evaporation and vapor pressure

3. A Molecular Comparison of Liquids and Solids

4. Intermolecular Forces
(intramolecular attraction)

5. Intermolecular Forces
London Dispersion Forces
Weakest of all intermolecular forces.
2 nonpolar molecules.
The nucleus of one molecule (or atom) attracts the electrons of the adjacent molecule (or atom).
A temporary polar molecule (dipole) is formed .

6. Intermolecular Forces
Dipole-Dipole Forces
Interaction between a dipole on one molecule and a dipole on an adjacent molecule.
Dipole-dipole forces exist between neutral polar molecules.

7. Intermolecular Forces
Hydrogen Bonding
A special case of dipole-dipole forces (IMAF, not bond!)
Strongest of the three Van der Waals forces (Hydrogen bonding, Dipole-dipole, London forces)
H directly bonded to an electronegative element (F, O, or N).

8. Intermolecular Forces
Ion-Dipole Forces
Interaction between an ion (Na+) and a dipole (water).
Strongest of all intermolecular forces

9. Practice
Draw the FCl molecule and label the positive and negative ends of the dipole. Compare with your partner.

10. Practice
Draw the FCl molecule and label the positive and negative ends of the dipole. Compare with your partner.
Use dotted lines to show the intermolecular forces. What are these IMFs called?

11. Practice
Draw the NH3 molecule and label the positive and negative ends of the dipole. Compare with your partner.

12. Practice
Draw the NH3 molecule and label the positive and negative ends of the dipole. Compare with your partner.
Use dotted lines to show the intermolecular forces. What are these IMFs called?

13. Properties of Liquids Melting/freezing
Change between solid and liquid phases
Standard molar enthalpy of fusion (DHofus)
The energy required to convert one mole of a solid at its melting point to a liquid.
6.02 kJ/mol for water
Conversion factor!

14. Properties of Liquids Melting/freezing
During a phase change, temperature does not change!

15. Properties of Liquids Vaporization Also called evaporation
Change from a liquid to a gas.
Standard molar enthalpy of vaporization (DHovap)
The energy required to convert one mole of a liquid at its boiling point to a gas.
40.6 kJ/mol for water
Conversion factor!

16. Practice
Ammonia (NH3) has a melting point of -78°C and a boiling point of -33°C.
Draw a heating diagram showing the melting and boiling points.
Label your diagram with phases – solid, liquid, gas. (Include where there are 2 together!)
Draw what the molecules would look like at each of the slanted parts.

17. Properties of Liquids Vapor Pressure Demonstration
Pressure exerted by a substance in the gas phase.
As temperature increases, vapor pressure increases.
Demonstration
Vapor pressure of different liquids.

18. Properties of Liquids Vapor Pressure Equilibrium
In a closed container, liquid particles evaporate while vapor particles condense
When the rate of condensation equals the rate of evaporation, the system reaches dynamic equilibrium
Before reaching
equilibrium:
rate of evaporation >
rate of condensation
After reaching equilibrium:
rate of evaporation = rate of condensation