1. Dr. Fred Omega Garces Chemistry 100 Miramar College
6.05 Intermolecular Forces Keeping Matter Together Nature’s Forces and the Magic of Water
Water crystal
Dr. Fred Omega Garces
Chemistry 100
Miramar College

2. Phases of Matter: Terminology
Energy is required for phase
changes to occur.
Solid-Liquid-Gas
Triangle

3. Heating Cooling Curve From Ice to Steam and Vice-versa 6.01 kJ mol
Stage1
Stage2
Stage3
Stage4
Stage5
40.7 kJ
mol
80 cal g
2.08 J
g °
0.43 cal
6.01 kJ mol
540 cal g
2.05 J
g °
0.49 cal J
g °
1 cal
g o
Heat Addition
What is the energy needed to take 1g H2O at 0°C to 100°C ?
=720cal

4. Intermolecular Forces
At the molecular level:
Molecules or matter is held together by “glue” called intermolecular forces
Energy added (K.E. increases)

5. Keeping Matter together
Intramolecular Forces -
Force which keeps molecule together, i.e., bonds.
Intermolecular Forces -
Attractive force between molecules. Responsible for keeping matter in solid or liquid phase.

6. The Forces be with You 2 Basic types of Intramolecular Force
Ion - Ion - Electrostatic attraction
Covalent Bonds - Mutual sharing of electrons
4 Basic types of Intermolecular Force*
Ion - dipole: Ion is attracted to polar molecule (NaCl in water)
2. dipole - dipole: Polar molecules attracted to each other.
3. dipole - induce dipole: Polar molecules attracted to nonpolar molecules. (Oxygen in water)
4. induce dipole -induce dipole (London dispersion forces, LDF) nonpolar molecules attraction for each other due to electron distortion.
* plus one

7. Relative Strength Interaction Example Energy
ion- ion Na+ Cl kJ
Covalent Bonds H - H kJ
ion-dipole (I-D) Na+ H2O kJ
dipole - dipole (D-D) HCl HCl kJ
dipole - induce dipole (D-ID) H2O O kJ
London Dispersion (LD) N2 N kJ
• H-Bond
kJ/mol

8. Property of Matter and IMF
IMF manifestation on the Property of matter
Boiling point – Temp. necessary to cause vapor pressure of liquid to equal 1 atm.
Melting point – Temperature necessary to cause solid to change to liquid.
Heats of Vaporization – Energy necessary to convert liquid to vapor
Heats of Fusion- Energy necessary to melt a solid
Specific Heat- Energy necessary to raise temperature one degree
Heat Capacity- Energy necessary to raise 1 gram substance one degree temperature
Surface tension – The force necessary to separate substances at the surface
Capillary action – The interaction between adhesive force versus cohesive force
Viscosity – The resistance for substance to flow
Vapor pressure – The pressure substance exert in a close container.

9. Review of Polarity
The Charge distribution may cancel out (nonpolar) or there may be a net distortion (polar)
Analogy:
1. No one wins: nonpolar
2. One team wins: polar
3. a) no one wins: nonpolar b) one team wins: polar c) two team wins polar

10. Ion - Ion Covalent Bonds
Ion - Ion: Electrostatic attraction between ions
Covalent Bonds: Bond between atoms as a result of electrons sharing.
Bond Energy: = 910 kJ/mol
Bond Energy: = 155 kJ/mol

11. Cation radius Enthalpy of Hydration
Ion - Dipole
Ion - Dipole: Charge and size dependent.
Most important for larger charge and small ionic radius.
Cation radius Enthalpy of Hydration
Ion (pm) (KJ/mol)
Li Na K Rb Cs
negative = energy release -
 +
Distance between ion center and negative pole of dipole

12. Dipole - Dipole
Dipole - Dipole: A permanent attractive intermolecular force resulting from the interaction of the positive end of one molecule with the negative end of another.
Dipole is based on D c EN. Bigger the difference, bigger the dipole.
Occurs between identical or different polar molecules.
NonPolar Polar
M (g/mol) bp (°C) M (g/mol) bp (°C)
N CO
SiH PH
GeH AsH
Br ICl

13. Induce dipole - induced dipole: London Dispersion Forces
-Br2
-Cl2
-F2
100 K
200 K
300 K
300 K
London Dispersion Force
(Induce dipole-Induce dipole):
Intermolecular force responsible for keeping nonpolar molecules (species) together.
Polarizability - The ease of which an e- cloud can be distorted. Larger the atomic size, the greater the number of electrons, the greater the polarizability.
Xe-
Kr-
Ar-
Ne-
He-
Boiling Point of the Halogens and Noble Gases
Halogen B.pt (K) Noble Gas B.pt (K)
F He 4.6
Cl Ne 27.3
Br Ar 87.5
I Kr 120.9
Xe 166.1

14. Boiling point versus polarizability
Graphs for family of chemicals that are polar and nonpolar; both show a fairly smooth increase of boiling point with atomic weight (larger degree of polarizability) due to increasing London Dispersion Forces

15. H2O: Nature of Water
The smaller the atom (element) the weaker the LDF Forces.
The bigger the atom (element) the stronger the LDF Forces
This is due to the polarizability of the larger elements
Molar Mass (Period)
H2Te
H2Se
SiH4
SbH3
GeG4
-100°C
0°C
100°C
Temperature HI
SnH4
PH3
AsH3
HCl
HBr
H2S

16. H2O: Nature of Water
Water is a liquid at room temperature as a direct consequence of hydrogen bonding between adjacent water molecules.
(Most other molecules with comparable molar mass are gas at room temperature)
Pure water is a liquid between 0°C and 100°C.
There is something else that is happening among the smaller N, O and F atoms that are bonded to Hydrogen however.
100°C
H2O HF
0°C
H2Te
NH3
SbH3
H2Se HI
H2S
AsH3
SnH4
-100°C
HCl
HBr
PH3
GeG4
Temperature
SiH4
CH4
Molar Mass (Period)

17. A Special Type of Bonding: H-Bonding
H-Bonding: A special glue above and beyond dipole-dipole intermolecular forces.
H2O molecules Alignments via H-bonding
H-bonding is a strong type of intermolecular force (bond) between hydrogen and very electronegative elements ( kJ/mol).
N-H O-H F-H also consider chlorine (Cl-H)
Biochemical structural Integrity.
Water possesses H-bond: Responsible for water’s unique properties.

18. Biological Integrity
H-bonding is responsible for the structural integrity of Biological molecules.
• Protein structures • DNA and RNA

19. Determining IMF at Work
The IMF present for matter will depend on the identity of the chemical present. For polar chemicals, dipole-dipole interaction exist as well as LDF. Dipole-dipole is the dominant IMF for polar chemicals however. For polar chemical in which H is bonded to F, N, O and Cl then in addition to the above mentioned IMF, H-bonding, the dominant IMF, is also present. For nonpolar chemicals, then LDF is the only force present. The magnitude of the IMF depends on the polarizability (LDF), dipole moment (dipole-dipole), number of H-X (H-bonding).

20. Example: H-bonding b) CH3OH f) H3CCH2OH c) H3CCONH2 g) H3CCOCH3
Which of the following substances exhibits H-bonding? Draw the H bonds between two molecules of the substances where appropriate.
a) C2H6 e) H3CCOOH
b) CH3OH f) H3CCH2OH
c) H3CCONH2 g) H3CCOCH3
d) H3C-CF3 h) H2C=O

21. Example: H-bonding a) C2H6 e) H3CCOOH No Yes b) CH3OH f) H3CCH2OH
Which of the following substances exhibits H-bonding? Draw the H bonds between two molecules of the substances where appropriate.
a) C2H6 e) H3CCOOH
No Yes
b) CH3OH f) H3CCH2OH
Yes Yes
c) H3CCONH2 g) H3CCOCH3
Yes No
d) H3C-CF3 h) H2C=O
No No

22. Example: IMF Determine type of IM forces Molecule LDF Dipole-Dipole
H-bonding
Polar or nonpolar
C2H6 X NP
CH3OH P
CH3F
H3C-O-CH3
NH3
F3C-NF3

23. Example ion-dipole dipole-dipole H-bond dipole-dipole
Identify the dominant intermolecular forces for each of the following substances, select the dominant IMF and select the substance with the higher boiling point in each pair;
a) MgCl2 or PCl3 b) H3CNH2 or CH3F
ion-dipole dipole-dipole H-bond dipole-dipole
LDF LDF dipole-dipole LDF
Higher Bpt LDF
Higher Bpt
c) CH3OH or CH3CH2OH e) Hexane or cyclohexane
H-bond H-bond LDF LDF
dipole-dipole dipole-dipole Higher Bpt
LDF LDF More surface area
Higher MWt.

24. Example ion-ion dipole-dipole H-bond dipole-dipole
Identify the dominant intermolecular forces for each of the following substances, select the dominant IMF and select the substance with the higher boiling point in each pair;
a) MgCl2 or PCl3 b) H3CNH2 or CH3F
ion-ion dipole-dipole H-bond dipole-dipole
ion-dipole LDF dipole-dipole LDF
LDF LDF
Higher Bpt Higher Bpt
c) CH3OH or CH3CH2OH e) Hexane or cyclohexane
H-bond H-bond LDF LDF
dipole-dipole dipole-dipole More surface area
LDF LDF (More polariable) Higher Bpt
Higher MWt.
Higher BPt

25. Summary of Nature’s Forces
Bonding forces are relatively strong because they involve larger charges that are closer together. Ionic ( kJ/mol) Covalent ( kJ/mol)
Intermolecular forces are relatively weak because they typically involve smaller charges that are farther apart. H-bond (10-40 kJ/mol) LDF ( kJ/mol)

26. Overview: Recognizing Intermolecular Forces (IMF)
Flowchart for recognizing the major types of intermolecular forces. London dispersion forces occur in all instances. The strength of other forces generally increases proceeding from left to right

27. IMF and Matter Three States of Matter Solid - liquid - gas
Intramolecular Forces
Ionic Bonds & Covalent Bonds
Intermolecular Forces
Ion-Dipole
Dipole - Dipole
ion-induced dipole
dipole- induced dipole
London Dispersion Forces
H-Bonding
Water’s Unique Property
to be covered …

28. Physical Properties of Matter
Density(solid) – Mass of substance for the volume it occupies
Surface tension – The force necessary to separate substances at the surface
Capillary action – The interaction between adhesive force versus cohesive force
Specific Heat- Energy necessary to raise temperature
Heats of Fusion- Energy necessary to melt a solid
Heats of Vaporization – Energy necessary to convert liquid to vapor
Viscosity – The resistance for substance to flow
Boiling point – Temp. necessary to cause vapor pressure of liquid to equal 1 atm.
Melting point – Temperature necessary to cause solid to change to liquid.
Vapor pressure – The pressure substance exert in a close container.

29. IMF and Water’s Unique Property
Properties:
Density(solid) - low density
Surface tension - bugs walking on water
Capillary action - method of which trees drink
Specific Heat-highest among all liquids and solids
Viscosity - high viscosity
Boiling point / melting point - higher than expected: Heat of fusion/Vaporization
Vapor pressure - low vapor pressure
Comparison with Other substances
Importance in physical and Biological Environment
Property
Prevents rapid temperature changes; heat transfer by water movement is very large; tends to maintain body temperature
Specific heat
(=4.18 J/g•K)
Highest of all liquids and solids except NH3
Heat of fusion
(=333 J/g)
Highest except for NH3
Thermostatic effect at freezing point due to absorption or release of heat
Heat of vaporization
(=2250 J/g)
Highest of all substances
Important in heat and water transfer within the atmosphere
Surface tension
(=7.2•109 N/m)
Highest of all liquids
Important in the physiology of cells; controls certain surface phenomena and the behavior and formation of drops
Conduction of heat
Highest of all liquids
Viscosity
(=10-2 N•s/m2)
Less than most liquids at comparable temperature
Flows readily to equalize pressure
Dielectric constant (=80 at 20°C)
Less of all liquids except H2O2 and HCN
Able to keep ions separate in solution

30. Water: Universal Solvent
Water, carbon tetrachloride (CCl4) and iodine. A) Water (a polar molecule) and CCl4 (a nonpolar molecule) are immiscible, with the more dense water layer found on top of the nonpolar CCl4 layer. A small amount of iodine is added in water to give a brown solution (top) - although only a small amount of iodine is dissolved in water. B) The mixture in A is then stirred. The nonpolar molecule I2 is more soluble in nonpolar CCl4 as indicated by the the dark color of the I2 in the CCl4 layer.
H-bonding network between water molecules.

31. H2O: Density
Water has a higher density than most material as a result most insoluble material floats.
The density of water increases slightly with increasing temperature between 0°C and 3.98 °C, where it reaches its maximum value.
For a great majority of substances, the solid state is more dense than the liquid. The fact that water shows the reverse behavior means that lakes freeze from the top down, not the bottom up. This topsy-turvy behavior is convenient for aqueous plants, fish, and ice skaters.
This same property has dangerous consequence for living cells. When living tissue freeze (frostbite) the ice crystals expands the cells and eventually rupture the cell.

32. H2O: Surface tension Water has a high surface tension.
The tendency for liquids to maintain a minimum surface area is most clearly seen in the formation of spherical drops in a rain showers. This is due to the forces experience at the surface to that in the interior. In the interior each and every molecule is surrounded by other molecules; therefore, the intermolecular attractions extend in every direction equally. Not so on the surface. A liquid molecule at the surface is attracted more to other liquid molecules beneath it rather than to the gas molecules above it Therefore, there is a preferential pull toward the center of the liquid. This pull called the surface tension, crowds the molecules on the surface, thereby establishing a layer that is tough to penetrate.
Molecules at surface is attracted only to molecules below and besides. The unevenness of attraction causes surface to contract making it act like a skin.
Molecules in the interior is attracted by surrounding molecules.

33. H2O: Capillary action How do plants drink water?
Polar liquids typically spontaneously rise up a narrow tube. Two different types of forces are responsible for this property: Cohesive forces, the intermolecular forces within the molecules in the liquid; Adhesive forces, the attraction between the liquid molecules and the container (stem). The cohesive force results in surface tension where as adhesive force occur when a container (cellulose of stem) contains many oxygen atoms (hydrophilic components) in which the partial negative charges of the oxygen are attractive to the positive end of water (the hydrogen) to form hydrogen bonding.
For Water: FAdhesive > F Cohesive
For Mercury: FCohesive > F Adhesive

34. H2O: Heat Capacity
Water absorbs large amounts of heat without the temperature changing. This is due to energy going into the breaking down of H-bonding before going into molecule kinetic energy.
Heat capacity of water is 10 times greater than Cu or Fe.
The heat capacity of water accounts for the moderate climate for communities near oceans or lakes. The temperature of the earth is 59°F (15°C) compared to the moon (-387°F to +253°F, 225°F avg) or Mars (-220°F to +70°F, -81°F average ) temperature which are very extreme.

35. Planet without Water Imagine an Earth Without Water
Liquid water has an unusually high specific heat capacity of nearly 4.2 J/g•K, about six times that of rock (~0.7 J/g•K). If the Earth were devoid of oceans, the Sun’s energy would heat a planet composed of rock. It would take only 0.7 J ( or cal) of energy to increase the temperature of each gram of rock by 1-degree. Daytime temperatures would soar easily into the several hundred °C. Because we have water on the Earth surface, the average temperature on Earth is 59°C. The oceans also limit the temperature drop when the Sun sets, because the energy absorbed during the day is released at night. If the Earth had a rocky surface, temperatures would be frigid every night.

36. H2O: Heat of Vaporization
Water has the highest heat of vaporization, consequently it has a very large cooling effect during the evaporation process. Evaporating water molecules removes a considerable amount of energy.

37. Vapor Pressure
Evaporation occurs when molecules have sufficient energy to escape the interface of a liquid substance.
Vapor Pressure - The pressure exerted by the liquid’s vapor at equilibrium.
Normal Boiling Point - The temperature at which the vapor pressure of a liquid equals the atmospheric pressure.

38. Phase Diagram (Revisited)
Heating - Cooling Curves and their relation to the Phase Diagram

39. Summary IMF is the phenomena responsible for the phases of matter.
Water has all three IMF; LDF, DD and H-Bond. These forces makes water a special molecule. It has stronger IMF than other molecules of the same size. This manifest itself in water having properties mentioned.