Presentation on theme: "Intermolecular Forces and"— Presentation transcript:
1 Intermolecular Forces and Liquids and SolidsChapter 11
2 Depends on the intermolecular distance A phase is a homogeneous part of the system in contact with other parts of the system but separated from them by a well-defined boundary.2 PhasesSolid phase - iceLiquid phase - waterDepends on the intermolecular distance
3 Intermolecular Forces Intermolecular forces are attractive forces between molecules.Intramolecular forces hold atoms together in a molecule.Intermolecular vs Intramolecular41 kJ to vaporize 1 mole of water (inter)930 kJ to break all O-H bonds in 1 mole of water (intra)“Measure” of intermolecular forceboiling pointmelting pointDHvapDHfusDHsubGenerally, intermolecular forces are much weaker than intramolecular forces.Chemical bonding and physical properties!
4 Intermolecular Forces Dipole-Dipole ForcesAttractive forces between polar moleculesOrientation of Polar Molecules in a SolidSo higher dipole, larger attractive force.
5 Intermolecular Forces Ion-Dipole ForcesAttractive forces between an ion and a polar moleculeIon-Dipole InteractionSmall r, larger F
6 Interaction Between Water and Cations Hydration(水合)in solution
7 Intermolecular Forces Dispersion Forces分散力(also be called as London Force)Attractive forces that arise as a result of temporary dipoles induced in atoms or moleculesion-induced dipole interactiondipole-induced dipole interaction
8 Dispersion Forces極化率The polarizability: the ability to distortion the electron distributionof a molecular or atoms.Normally, large amount of electrons or low-density electroncloud will show higher polarizationDispersion force is the transition of the dipole-induced attractionSo He or N2 gas/non-polarized maculars can be condensedin low-temperature.
9 Induced Dipoles Interacting With Each Other Transition state
10 Intermolecular Forces Dispersion Forces ContinuedPolarizability is the ease with which the electron distribution in the atom or molecule can be distorted.Polarizability increases with:greater number of electronsmore diffuse electron cloudDispersion forces usually increase with molar mass.Some dispersion force larger than polarized dipole-dipole force!e.g. CCl4 (76.5o)shows higher boiling point than CH3F(-78.4o)
11 What type(s) of intermolecular forces exist between each of the following molecules? HBrHBr is a polar molecule: dipole-dipole forces. There are also dispersion forces between HBr molecules.CH4CH4 is nonpolar: dispersion forces.SOSO2SO2 is a polar molecule: dipole-dipole forces. There are also dispersion forces between SO2 molecules.
12 Intermolecular Forces Hydrogen BondThe hydrogen bond is a special dipole-dipole interaction between they hydrogen atom in a polar N-H, O-H, or F-H bond and an electronegative O, N, or F atom.AH…BorA & B are N, O, or F
13 Why is the hydrogen bond considered a “special” dipole-dipole interaction? Decreasing molar massDecreasing boiling point
15 The average hydrogen bond is ~ 40KJ/mol. The strength of hydrogen bond depends on the electronegativityOf atoms.e.g. HF shows higher strength than H2O. However, H2O showsHigher boiling point than HF? Each H2O have 4 H-bond.
16 Strong intermolecular forces Properties of LiquidsSurface tension is the amount of energy required to stretch or increase the surface of a liquid by a unit area.Strong intermolecular forcesHigh surface tension
17 H2O show very strong H-bond, therefore shows higher surface tension than other liquid
18 Polarized molecular and non-polarized molecular
19 Properties of LiquidsCohesion is the intermolecular attraction between like moleculesAdhesion is an attraction between unlike moleculesAdhesionCohesion
20 Strong intermolecular forces Properties of LiquidsViscosity is a measure of a fluid’s resistance to flow.Strong intermolecular forcesHigh viscosity
21 Similar to H2O, it shows high H-bond ViscosityCH2-OH甘油Similar to H2O, it shows high H-bond
22 Ice is less dense than water 3-D Structure of WaterWater is a Unique Substance2 共價鍵2氫鍵Maximum Density4°CDensity of WaterIce is less dense than water
24 Unit cells in 3 dimensions A crystalline solid possesses rigid and long-range order. In a crystalline solid, atoms, molecules or ions occupy specific (predictable) positions.An amorphous solid does not possess a well-defined arrangement and long-range molecular order.A unit cell is the basic repeating structural unit of a crystalline solid.latticepointAt lattice points:AtomsMoleculesIonsUnit CellUnit cells in 3 dimensions
32 When silver crystallizes, it forms face-centered cubic cells When silver crystallizes, it forms face-centered cubic cells. The unit cell edge length is 409 pm. Calculate the density of silver.d =mVV = a3= (409 pm)3 = 6.83 x cm34 atoms/unit cell in a face-centered cubic cell107.9 gmole Agx1 mole Ag6.022 x 1023 atomsxm = 4 Ag atoms= 7.17 x gd =mV7.17 x g6.83 x cm3== 10.5 g/cm3
44 Types of Crystals Ionic Crystals Lattice points occupied by cations and anionsHeld together by electrostatic attractionHard, brittle, high melting pointPoor conductor of heat and electricityCsClZnSCaF2
47 Types of Crystals Covalent Crystals Lattice points occupied by atoms Held together by covalent bondsHard, high melting pointPoor conductor of heat and electricitycarbonatomsdiamondgraphite
48 From graphite to graphene Slice down toAtomic layer
49 What is graphene?Imagine a piece of paper but a million times thinner. This is how thick graphene is.The thinnest while strongest material in the world!(0.77 mg/1m2 Graphene, can sustain 4 kg )Imagine a material more conducting than silver. This is how conductive graphene is.Image from Nobel committeeFrom a recently interview with A. K. Geim.
50 Electrical properties of Graphene Graphene resistivity: 1.0x10-8 Ohm mAlso, it’s current density is > 1.0X108 A/cmFrom wikipedia
51 Mechanical properties Graphene : ~1000 GPaFrom wikipedia
52 Thermal conductivityGraphene : ~5300 W/mKMovieFrom wikipedia
54 Carrier mobility in graphene : 1/300 of light speed Low energy is like a massless 2D Dirac modelZero band gap semiconductor.Carrier shows Lineardispersion around Femi- level.The electronic behaviorcan be described byQM ‘s Dirac equation.4. In condense physic :The unique MasslessDirac fermionsKK’M石墨烯更为奇特之处是它具有独特的电子结构和电学性质.石墨烯的价带(π 电子)和导带(π*电子)相交于费米能级处(K 和K′点), 是能隙为零的半导体,Ballistic transport on submicron to micron distances.IBM already demonstrated 100 GHz high frequency device.Dispersion: Dr. Thomas Szkopek, McGill University
59 Cross Section of a Metallic Crystal Types of CrystalsMetallic CrystalsLattice points occupied by metal atomsHeld together by metallic bondsSoft to hard, low to high melting pointGood conductors of heat and electricity(high density)Cross Section of a Metallic Crystalnucleus &inner shell e-mobile “sea”of e-
66 The equilibrium vapor pressure is the vapor pressure measured when a dynamic equilibrium exists between condensation and evaporationH2O (l) H2O (g)Rate ofcondensationevaporation=Dynamic Equilibrium
67 Measurement of Vapor Pressure BeforeEvaporationAt Equilibrium
68 Vapor Pressure Versus Temperature Molar heat of vaporization (DHvap) is the energy required to vaporize 1 mole of a liquid at its boiling point.ln P = -DHvapRT+ CClausius-Clapeyron EquationP = (equilibrium) vapor pressureT = temperature (K)R = gas constant (8.314 J/K•mol)Vapor Pressure Versus Temperature
69 Alternate Forms of the Clausius-Clapeyron Equation At two temperaturesor
70 The boiling point is the temperature at which the (equilibrium) vapor pressure of a liquid is equal to the external pressure.The normal boiling point is the temperature at which a liquid boils when the external pressure is 1 atm.
71 The critical temperature (Tc) is the temperature above which the gas cannot be made to liquefy, no matter how great the applied pressure.The critical pressure (Pc) is the minimum pressure that must be applied to bring about liquefaction at the critical temperature.
72 The Critical Phenomenon of SF6 T < TcT > TcT ~ TcT < Tc
73 Solid-Liquid Equilibrium H2O (s) H2O (l)The melting point of a solid or the freezing point of a liquid is the temperature at which the solid and liquid phases coexist in equilibrium
74 Molar heat of fusion (DHfus) is the energy required to melt 1 mole of a solid substance at its freezing point.
75 Solid-Gas Equilibrium H2O (s) H2O (g)Molar heat of sublimation (DHsub) is the energy required to sublime 1 mole of a solid.DHsub = DHfus + DHvap( Hess’s Law)
76 A phase diagram summarizes the conditions at which a substance exists as a solid, liquid, or gas. Phase Diagram of Water
77 Phase Diagram of Carbon Dioxide At 1 atmCO2 (s) CO2 (g)
78 Effect of Increase in Pressure on the Melting Point of Ice and the Boiling Point of Water
79 CH11 Homework12.98 Given the phase diagram of carbon shown here, answer these questions: (a) How many triple points are there and what are the phases that can coexist at each triple point? (b) Which has a higher density, graphite or diamond? (c) Synthetic diamond can be made from graphite. Using the phase diagram, how would you go about making diamond?12.20 Explain the difference in the melting points of these compounds:
80 12. 80 The vapor pressure of benzene, C6H6, is 40. 1 mmHg at 7. 6°C 12.80 The vapor pressure of benzene, C6H6, is 40.1 mmHg at 7.6°C. What is its vapor pressure at 60.6°C? The molar heat of vaporization of benzene is 31.0 kJ/mol.