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Intermolecular Forces: Liquids, Solids, and Phase Changes

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1 Intermolecular Forces: Liquids, Solids, and Phase Changes
Chapter 12 Intermolecular Forces: Liquids, Solids, and Phase Changes

2 Intermolecular Forces: Liquids, Solids, and Phase Changes
12.1 An Overview of Physical States and Phase Changes 12.2 Quantitative Aspects of Phase Changes 12.3 Types of Intermolecular Forces 12.4 Properties of the Liquid State 12.5 The Uniqueness of Water 12.6 The Solid State: Structure, Properties, and Bonding 12.7 Advanced Materials

3 A Macroscopic Comparison of Gases, Liquids, and Solids
Table 12.1 A Macroscopic Comparison of Gases, Liquids, and Solids State Shape and Volume Compressibility Ability to Flow Gas Conforms to shape and volume of container high high Liquid Conforms to shape of container; volume limited by surface very low moderate Solid Maintains its own shape and volume almost none almost none

4 Types of Phases Changes
A liquid changing into a gas - vaporization; the reverse process - condensation A solid changing into a liquid - fusion (melting); the reverse process - freezing (solidification) A solid changing directly into a gas - sublimation; the reverse process - deposition Enthalpy changes accompany phase changes. Vaporization, fusion, and sublimation are EXOTHERMIC; the reverse processes ENDOTHERMIC

5 Heats of vaporization and fusion for several common substances.

6 Phase changes and their enthalpy changes

7 Quantitative Aspects of Phase Changes
Energy changes result in a change in temperature and/or change in phase. Within a phase, a change in heat is accompanied by a change in temperature which is associated with a change in average Ek as the most probable speed of the molecules changes. q = (amount)(molar heat capacity)(DT) During a phase change, a change in heat occurs at a constant temperature, which is associated with a change in Ep, as the average distance between molecules changes. q = (amount)(enthalpy of phase change)

8 A cooling curve for the conversion of gaseous water to ice
Heat Removed

9 Calculating the Loss of Heat -
Cooling steam at 110o C down to ice at -10o C q = (amount)(molar heat capacity)(DT) - change of temp q = (amount)(enthalpy of phase change) - change of phase q = n Cwater(g) ( ) + q = n (-HOvap) + q = n Cwater(l) (0-100) + q = n (-HOfus) + q = n Cwater(s) (-10-0) =

10 Liquid-gas equilibrium

11 The effect of temperature on the distribution of molecular speed in a liquid

12 Vapor pressure as a function of temperature and intermolecular forces
A linear plot of vapor pressure- temperature relationship

13 The Clausius-Clapeyron Equation
Subtraction two equations for two temperatures.

14 SAMPLE PROBLEM 12.1 Using the Clausius-Clapeyron Equation PROBLEM: The vapor pressure of ethanol is 115 torr at 34.90C. If DHvap of ethanol is 40.5 kJ/mol, calculate the temperature (in 0C) when the vapor pressure is 760 torr. PLAN: We are given 4 of the 5 variables in the Clausius-Clapeyron equation. Substitute and solve for T2. SOLUTION: 34.90C = 308.0K 1 T2 308K - ln 760 torr 115 torr -40.5 x103 J/mol 8.314 J/mol*K = T2 = 350K = 770C

15 Phase diagrams for CO2 and H2O

16 Types of Intermolecular Forces - Bonding and Nonbonding

17 Types of Intermolecular Forces - Bonding and Nonbonding

18 Orientation of polar molecules because of dipole-dipole forces

19 Dipole moment and boiling point

20 The Hydrogen Bond A special dipole-dipole interaction occurs when a H atom is covalently bonded to a small electronegative atom, i.e. N, O, or F. The Hydrogen Bond is a through space bond between a H atom that is covalently bonded to one of the electronegative atoms to another of the electronegative atoms. H-F-----H-O-H H2O------H-O-O

21 SAMPLE PROBLEM 12.2 Drawing Hydrogen Bonds Between Molecules of a Substance PROBLEM: Which of the following substances exhibits H bonding? For those that do, draw two molecules of the substance with the H bonds between them. (c) (a) (b) PLAN: Find molecules in which H is bonded to N, O or F. Draw H bonds in the format -B: H-A-. SOLUTION: (a) C2H6 has no H bonding sites. (b) (c)

22 Hydrogen bonding and boiling point

23 The H-bonding abilitiy of the water molecule

24 separated Cl2 molecules instantaneous dipoles
DISPERSION (London) FORCES among nonpolar molecules instantaneous dipoles

25 Effect of Molar Mass and boiling point
DISPERSION (London) FORCES Effect of Molar Mass and boiling point

26 DISPERSION (London) FORCES
Molecular shape and boiling point

27 SAMPLE PROBLEM 12.3 Predicting the Type and Relative Strength of Intermolecular Forces PROBLEM: For each pair of substances, identify the dominant intermolecular forces in each substance, and select the substance with the higher boiling point. (a) MgCl2 or PCl3 (b) CH3NH2 or CH3F (c) CH3OH or CH3CH2OH (d) Hexane (CH3CH2CH2CH2CH2CH3) or 2,2-dimethylbutane PLAN: Bonding forces are stronger than nonbonding(intermolecular) forces. Hydrogen bonding is a strong type of dipole-dipole force. Dispersion forces are decisive when the difference is molar mass or molecular shape.

28 SAMPLE PROBLEM 12.3 Predicting the Type and Relative Strength of Intermolecular Forces continued SOLUTION: (a) Mg2+ and Cl- are held together by ionic bonds while PCl3 is covalently bonded and the molecules are held together by dipole-dipole interactions. Ionic bonds are stronger than dipole interactions and so MgCl2 has the higher boiling point. (b) CH3NH2 and CH3F are both covalent compounds and have bonds which are polar. The dipole in CH3NH2 can H bond while that in CH3F cannot. Therefore CH3NH2 has the stronger interactions and the higher boiling point. (c) Both CH3OH and CH3CH2OH can H bond but CH3CH2OH has more CH for more dispersion force interaction. Therefore CH3CH2OH has the higher boiling point. (d) Hexane and 2,2-dimethylbutane are both nonpolar with only dispersion forces to hold the molecules together. Hexane has the larger surface area, thereby the greater dispersion forces and the higher boiling point.

29 Crystal Structures and the Unit Cell
There are three types of cubic unit cells 1) Simple Cubic Unit Cell - 1 atom per unit cell 2) Body-Centered Cubic Unit Cell - 2 atoms per unit cell 3) Face-Centered Cubic Unit Cell - 4 atoms per unit cell

30 The crystal lattice and the unit cell

31 The three cubic unit cells
Figure (1 of 3) The three cubic unit cells Simple Cubic 1/8 atom at 8 corners Atoms/unit cell = 1/8 * 8 = 1 coordination number = 6

32 The three cubic unit cells
Figure (2 of 3) The three cubic unit cells Body-centered Cubic coordination number = 8 1/8 atom at 8 corners 1 atom at center Atoms/unit cell = (1/8*8) + 1 = 2

33 The three cubic unit cells
Figure (3 of 3) The three cubic unit cells Face-centered Cubic coordination number = 12 1/8 atom at 8 corners 1/2 atom at 6 faces Atoms/unit cell = (1/8*8)+(1/2*6) = 4

34 Packing of spheres Figure 12.28 simple cubic (52% packing efficiency)
body-centered cubic (68% packing efficiency)

35 hexagonal closest packing cubic closest packing layer a layer c
Figure (continued) layer a layer b hexagonal closest packing cubic closest packing layer a layer c closest packing of first and second layers abab… (74%) hexagonal unit cell abcabc… (74%) expanded side views face-centered unit cell

36 SAMPLE PROBLEM 12.4 Determining Atomic Radius from Crystal Structure PROBLEM: Barium is the largest nonradioactive alkaline earth metal. It has a body-centered cubic unit cell and a density of 3.62 g/cm3. What is the atomic radius of barium? (Volume of a sphere: V = 4/3pr3) PLAN: We can use the density and molar mass to find the volume of 1 mol of Ba. Since 68%(for a body-centered cubic) of the unit cell contains atomic material, dividing by Avogadro’s number will give us the volume of one atom of Ba. Using the volume of a sphere, the radius can be calculated. density of Ba (g/cm3) radius of a Ba atom reciprocal divided by M V = 4/3pr3 volume of 1 mol Ba metal volume of 1 Ba atom multiply by packing efficiency volume of 1 mol Ba atoms divide by Avogadro’s number

37 SAMPLE PROBLEM 12.4 Determining Atomic Radius from Crystal Structure continued SOLUTION: 1 cm3 3.62 g x 137.3 g Ba mol Ba Volume of Ba metal = = 37.9 cm3/mol Ba 37.9 cm3/mol Ba x 0.68 = 26 cm3/mol Ba atoms 26 cm3 mol Ba atoms x mol Ba atoms 6.022x1023 atoms = 4.3x10-23 cm3/atom r3 = 3V/4p = 2.2 x 10-8cm

38 End of Chapter 12

39 Cubic closest packing of frozen methane
Figure 12.29 Figure 12.30 Cubic closest packing of frozen methane Cubic closest packing for frozen argon

40 Table 12.5 Characteristics of the Major Types of Crystalline Solids
Interparticle Forces Physical Behavior Particles Examples (mp,0C) Atomic Atoms Dispersion Soft, very low mp, poor thermal & electrical conductors Group 8A(18) [Ne-249 to Rn-71] Molecular Molecules Dispersion, dipole-dipole, H bonds Fairly soft, low to moderate mp, poor thermal & electrical conductors Nonpolar - O2[-219], C4H10[-138], Cl2 [-101], C6H14[-95] Polar - SO2[-73], CHCl3[-64], HNO3[-42], H2O[0.0] Ionic Positive & negative ions Ion-ion attraction Hard & brittle, high mp, good thermal & electrical conductors when molten NaCl [801] CaF2 [1423] MgO [2852] Metallic Atoms Metallic bond Soft to hard, low to very high mp, excellent thermal and electrical conductors, malleable and ductile Na [97.8] Zn [420] Fe [1535] Network Atoms Covalent bond Very hard, very high mp, usually poor thermal and electrical conductors SiO2 (quartz)[1610] C(diamond)[4000]

41 The sodium chloride structure
Figure 12.31 The sodium chloride structure

42 The zinc blende structure
Figure 12.32 The zinc blende structure

43 The fluorite (CaF2) structure
Figure 12.33

44 Crystal structures of metals
Figure 12.34 Crystal structures of metals hexagonal closest packing cubic closest packing

45 Crystalline and amorphous silicon dioxide
Figure 12.35 Crystalline and amorphous silicon dioxide

46 The band of molecular orbitals in lithium metal
Figure 12.36 The band of molecular orbitals in lithium metal

47 Electrical conductivity in a conductor, semiconductor, and insulator
Figure 12.37 Electrical conductivity in a conductor, semiconductor, and insulator conductor insulator semiconductor

48 The molecular basis of surface tension
Figure 12.19 The molecular basis of surface tension

49 The hexagonal structure of ice
Figure 12.22 The hexagonal structure of ice

50 The macroscopic properties of water and their atomic and molecular “roots”.
Figure 12.24

51 Surface Tension (J/m2) at 200C
Table 12.3 Surface Tension and Forces Between Particles Surface Tension (J/m2) at 200C Substance Formula Major Force(s) diethyl ether CH3CH2OCH2CH3 1.7x10-2 dipole-dipole; dispersion ethanol CH3CH2OH 2.3x10-2 H bonding butanol CH3CH2CH2CH2OH 2.5x10-2 H bonding; dispersion water H2O 7.3x10-2 H bonding mercury Hg 48x10-2 metallic bonding

52 stronger cohesive forces
Figure 12.20 Shape of water or mercury meniscus in glass stronger cohesive forces adhesive forces

53 Table 12.4 Viscosity of Water at Several Temperatures
Viscosity (N*s/m2)* Temperature(0C) 20 1.00x10-3 40 0.65x10-3 60 0.47x10-3 80 0.35x10-3 *The units of viscosity are newton-seconds per square meter.

54 Periodic trends in covalent and van der Waals radii (in pm)
Figure 12.11

55 Covalent and van der Waals radii
Figure 12.10 Covalent and van der Waals radii

56

57 Crystal structures and band representations of doped semiconductors
Figure 12.39 Crystal structures and band representations of doped semiconductors

58 p-n junction Figure 12.40 Forward bias The p-n junction Reverse bias

59 Steps in manufacturing a p-n junction
Figure 12.41 heat in furnace with O2 treat with photoresist apply template expose to light and solvent remove template treat with Ga vapor remove SiO2 etch SiO2 with HF remove photoresist

60 Structures of two typical liquid crystal molecules
Figure 12.42

61 The three common types of liquid crystal phases
Figure 12.43 The three common types of liquid crystal phases

62 Schematic of a liquid crystal display (LCD)
Figure 12.45 Schematic of a liquid crystal display (LCD)

63 Table 12.7 Some Uses of New Ceramics and Ceramic Materials
Applications SiC, Si3N4, TiB2, Al2O3 Whiskers(fibers) to strength Al and other ceramics Si3N4 Car engine parts; turbine rotors for “turbo” cars; electronic sensor units Si3N4, BN, Al2O3 Supports or layering materials(as insulators) in electronic microchips SiC, Si3N4, TiB2, ZrO2, Al2O3, BN Cutting tools, edge sharpeners(as coatings and whole devices), scissors, surgical tools, industrial “diamond” BN, SiC Armor-plating reinforcement fibers(as in Kevlar composites) ZrO2, Al2O3 Surgical implants(hip and knee joints)

64 Unit cells of some modern ceramic materials
Figure 12.46 SiC BN cubic boron nitride (borazon)

65 Table 12.8 Molar Masses of Some Common Polymers
Name Mpolymer (g/mol) n Uses Acrylates 2 x105 2 x103 Rugs, carpets Polyamide(nylons) 1.5 x104 1.2 x102 Tires, fishing line Polycarbonate 1 x105 4 x102 Compact disks Polyethylene 3 x105 1 x104 Grocery bags Polyethylene (ultra- high molecular weight) 5 x106 2 x105 Hip joints Poly(ethylene terephthalate) 2 x104 1 x102 Soda bottles Polystyrene 3 x105 3 x103 Packing; coffee cups Poly(vinyl chloride) 1 x105 1.5 x103 Plumbing

66 The random coil shape of a polymer chain
Figure 12.47

67 The semicrystallinity of a polymer chain
Figure 12.48 The semicrystallinity of a polymer chain

68 The viscosity of a polymer in solution
Figure 12.49

69 Table 12.9 Some Common Elastomers
Name Tg (0C)* Uses Poly(dimethyl siloxane) -123 Breast implants Polybutadiene -106 Rubber bands Polyisoprene -65 Surgical gloves Polychloroprene (neoprene) -43 Footwear; medical tubing *Glass transition temperature

70 tip of an atomic force microscope (AFM)
Figure 12.50 Manipulating atoms tip of an atomic force microscope (AFM)

71 Manipulating atoms nanotube gear
Figure 12.50 Manipulating atoms nanotube gear

72 Tools of the Laboratory
Figure B12.1 Diffraction of x-rays by crystal planes

73 Tools of the Laboratory
Figure B12.2 Formation of an x-ray diffraction pattern of the protein hemoglobin

74 Tools of the Laboratory
Figure B12.3 Scanning tunneling micrographs gallium arsenide semiconductor metallic gold


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