1. Chapter 11 (11.1-11.5) Intermolecular Forces, Liquids and Solids
CHEMISTRY The Central Science 9th Edition
Chapter 11 ( ) Intermolecular Forces, Liquids and Solids 1

2. 11.1: A Molecular Comparison of Liquids and Solids

3. The fundamental difference between states of matter is the strength of the intermolecular forces of attraction.
Stronger forces bring molecules closer together.
Solids and liquids are referred to as the condensed phases.

4. Some place between liquids and crystalline solids are Amorphous Solids
No regularly ordered pattern
Close packed particles
Motion limited to vibrations in place
The forces holding solids and liquids together are called intermolecular forces

5. Something to think about:
Using the particle nature of matter that was just presented, explain the following properties of solids, liquids and gases:
Compressibility
Volume and shape
Diffusion
Watch this: Is glass really a solid?

6. 11.2: Intermolecular Forces
The covalent bond holding a molecule together is an intramolecular force
The attraction between molecules is an intermolecular force
Much weaker than intramolecular forces
Melting or boiling: the intermolecular forces are broken (not the covalent bonds)
The stronger the attractive forces, the higher the boiling point of the liquid and the melting point of a solid

7. Ion-dipole forces exist between an ion and a polar molecule
Partial negative end of the water molecule and the positive sodium ion are held together by an ion-dipole force of attraction
Recall the process of solvation!
Bond breaking: endothermic
Bond making: exothermic

8. Dipole-dipole forces exist between neutral polar molecules in the liquid or solid state
Oppositely charged ends of molecules attract
Weaker than ion-dipole forces
Dipole-dipole forces increase with increasing polarity
Strength of attractive forces is inversely related to molecular volume

9. Text P. 449

10. London dispersion forces are the result of attractions between induced dipoles
Weakest of all intermolecular forces
Two adjacent neutral, nonpolar molecules
The nucleus of one attracts the electrons of the other
Electron clouds are distorted
Instantaneous dipole
Strength of forces is directly related to molecular weight
London dispersion forces exist between all molecules

11. Instantaneous dipoles for two He atoms
Text P. 447

12. London dispersion forces also depend on the shape of the molecule
The greater the surface area available for contact, the greater the dispersion forces
Text, P. 448

13. Something to think about:
Order the halogens according to increasing boiling points. Explain your reasoning.

14. Something to think about:
Order the halogens according to increasing boiling points. Explain your reasoning.

15. Watch this: Bozeman Science on Dipole Forces

16. Hydrogen bonding is an especially strong form of dipole-dipole force
H-bonding requires H bonded to an electronegative element (most important for compounds of F, O, and N)
The small size of electropositive hydrogen allows it to approach and form a strong force of attraction with a nonbonding electron pair on these very electronegative atoms

17. Hydrogen Bonding Text, P. 449
Boiling point increases with increasing molecular weight. The exception is water (H bonding)

18. Text, P. 451
- Solids are usually more closely packed than liquids (solids are more dense than liquids)
- Ice is ordered with an open structure to optimize H-bonding (ice is less dense than water)
Watch this: Don’t make this mistake with H bonding!

19. Dispersion forces<dipole-dipole<hydrogen bonding<ion-dipole
For molecules of similar size and mass, intermolecular forces of attraction increase in the following way:
Dispersion forces<dipole-dipole<hydrogen bonding<ion-dipole

20. Text, P. 453

21. 11.3: Some Properties of Liquids
Viscosity
Viscosity is the resistance of a liquid to flow
Molecules slide over each other
The stronger the intermolecular forces, the higher the viscosity
Viscosity increases with an increase in molecular weight

22. Surface Tension
Surface molecules are only attracted inwards towards the bulk molecules
Imbalance of IMFs at the surface of the liquid
Molecules within the liquid are all equally attracted to each other

23. Surface tension is the amount of energy required to increase the surface area of a liquid
Cohesive forces bind molecules to each other (Hg)
Adhesive forces bind molecules to a surface (H2O)
If adhesive forces > cohesive forces, the meniscus is U- shaped (water in a glass)
If cohesive forces > adhesive forces, the meniscus is curved downwards (Hg in a barometer)

24. 11.4: Phase Changes Text, P. 457 (Exothermic) (Endothermic)

25. Generally heat of fusion (melting 1 mole of a substance at constant T) is less than heat of vaporization (evaporation of 1 mole of a substance at constant T)
It takes more energy to completely separate molecules than to partially separate them
Text, P. 458

26. Plot of temperature change versus heat added is a heating curve
Heating Curves
Plot of temperature change versus heat added is a heating curve
During a phase change, adding heat causes no temperature change (equilibrium is established)
These points are used to calculate ΔHfus and ΔHvap
Remember: Q = m·Cp·ΔT
Watch this: Boiling and Evaporation

27. Added heat increases the temperature of a consistent state of matter
Text, P. 459
Added heat increases the temperature of a consistent state of matter
Energy used for changing molecular motion, no T change

28. Critical Temperature and Pressure
Gases are liquefied by increasing pressure at some temperature
Critical temperature: the maximum temperature for liquefaction of a gas using pressure
A high C.T. means strong intermolecular forces
At temperatures higher than the CT, KE is so great that the substance can only be in the gas phase
Critical pressure: pressure required for liquefaction at the CT
Brings the molecules sufficiently close together so that forces of attraction can take over

29. Nonpolar substances and those with low molar masses have low IMFs and low CT’s and CP’s
Polar substances and those with higher molar masses have higher CT’s and CP’s because they are more polarizable and have higher IMFs

30. 11.5: Vapor Pressure Explaining Vapor Pressure on the Molecular Level
Some of the molecules on the surface of a liquid have enough energy to escape to the gas phase
After some time the pressure of the gas will be constant at the vapor pressure (equilibrium is established)

31. Partial pressure of water vapor is constant
Dynamic Equilibrium: the point when as many molecules escape the surface as strike the surface
Partial pressure of water vapor is constant
Vapor pressure is the pressure exerted when the liquid and vapor are in dynamic equilibrium in a closed system
Text P. 462

32. Volatility, Vapor Pressure, and Temperature
If equilibrium is never established then the liquid evaporates
Nonpolar liquids having low molar masses usually have weak IMFs and (evaporate rapidly)
The higher the T, the higher the average KE, the faster the liquid evaporates (hot water evaporates faster than cold water)

33. Something to think about:
Place the following compounds in order of increasing vapor pressure:
CCl4 , Cl4 , CBr4 . Justify your answer
Watch This: Bozeman Science on Intermolecular Forces

34. Vapor pressure increases nonlinearly with increasing temperature
Text, P. 463

35. Vapor Pressure and Boiling Point
Liquids boil when the external pressure equals the vapor pressure
Normal BP: BP of a liquid at 1 atmosphere
Temperature of boiling point increases as pressure increases
Watch this: Boiling, atmospheric pressure and vapor pressure

36. Something to think about:
Predict whether glycerol, C3H5(OH)3 , or 1 propanol, C3H7OH, will have the higher:
Viscosity
Vapor pressure
Boiling point
Justify your response

37. Something to think about:
Ice skaters demonstrate that ice melts under pressure.
A skater glides over a liquid surface of water as her blades impart a force sufficient to temporarily melt the ice. What does this say about the relative densities of ice and liquid water?
Describe the molecular structures of liquid and solid water that would explain this unusual property of ice.

38. Something to think about:
Look at the picture on this page.
List the four liquids in order of increasing vapor pressure at any given temperature and give their formulas.
Justify the trend citing the intermolecular forces acting in each liquid.

39. End of Chapter 11 (11.1-11.5) Intermolecular Forces, Liquids and Solids