( Intermolecular Forces ) 之物质结构（之物质结构（3）分子间作用力分子间作用力Dr. Xiaogai Yang Department of Chemical BiologySchool of Pharmaceutical SciencesPeking UniversityEmail: yxgbjmu.edu.cnHow Drug works - A majority of pharmacologic responses are mediated through receptors-Weak Interactions Are Crucial to Macromolecular Structure and Function 云腾致雨 露结为霜 Intermolecular ForcesStates of MatterKinetic energies of the particle Intermolecular ForcesTemperatureThe boiling point and melting point increase with increasing The boiling point and melting point increase with increasing intermolecular forces.intermolecular forces.Molecular polarityMolecular polarityInstantaneous dipolePermanent dipoleIntermolecular forces are electrostatic forces. Intermolecular forces are electrostatic forces. The Origination of Intermolecular Forces Types of Intermolecular ForcesOrientation ForceInduction ForceLondon Dispersion ForceH-BondingIon-Dipole ForcesHydrophobic InteractionsOrientation ForceDipole Dipole ForcePolar moleculePolar moleculeInduction ForceDipole Induced Dipole ForcePolar moleculePolar moleculePolar moleculeNonpolar moleculeLondon Dispersion ForceInduced Dipole Induced Dipole ForcePolar moleculePolar moleculePolar moleculeNonpolar moleculeNonpolar moleculeNonpolar moleculePolarizabilityDispersion force tends to increase with increasing molecular massSummaryOrientation ForceInduction ForceDispersionForcePolar moleculePolar moleculePolar moleculeNonpolar moleculeNonpolar moleculeNonpolar moleculevan der Waals Forces分子偶极矩（实）/10-30Cm取向力/kJmol-1诱导力/kJmol-1色散力/kJmol-1总分子间作用力/kJmol-1沸点/KHI1.400.0250.11325.8726.00HBr2.670.690.50221.9423.11206.2HCl3.603.311.0016.8321.14189.2分子间作用能的分配ExerciseB.P. increase with the M.W. increasingExceptionException：HH2 2O, HF O, HF 和和和和NHNH3 3WHY WHY ?Except for van der Waals forces, there must be some other force氢键氢键 (H-Bonding)XH-YNOFFNO极性共价键极性共价键an unshared electron pairOne of the smaller atoms-X相同-Y相同-X,Y均相同-A hydrogen bond is an attractive interaction between an unshared electron pair on an electronegative O, N, and F and a positively polarized hydrogen atom bonded to another O, N, or F.high boiling pointslow boiling points分子间缔合，沸点升高，熔点升高分子间缔合，沸点升高，熔点升高-可形成分子间或分子内氢键可形成分子间或分子内氢键Inter- & intra-molecular hydrogen bondA water molecule can form up to four hydrogen bonds.Hydrogen bonding by a water molecule around a molecule in the solid in the liquidStructure and Properties of WaterBecause of Hydrogen Bonding.lWater has a uniquely high specific heat (1 cal/gC) and a uniquely high heat of vaporization (541.6 cal/g).Thermal regulation of the climate. Absorbs heat during the day (vaporization of water)Warms the earth during the night (dew etc.).lThe density of solid water is less than liquid water. Very unusual.This allows life to exist in our oceans and lakes.DNA分子中存在氢键分子中存在氢键Ion-Dipole Forces- Interaction between an ion (Na+) and a dipole (water).- Strongest of all intermolecular forcesHydrophobic Interactions-The tendency of nonpolar molecules to self-associate in water defined as hydrophobic effect. StraightflushJunkJohnshandDaveshand1878年，年，L.Boltzman提出了熵与微观状态数的关系提出了熵与微观状态数的关系S =k lnW W:thenumberofpossiblearrangementsinthesystem k:Boltzmanns constant-The driving force is increased solvent entropy. Weak Interactions Are Crucial to Macromolecular Structure and Function InteractionExampleEnergy离子键离子键Na+ Cl- 400 -4000 kJ/mol共价键共价键 H - H 150-1100 kJ/molion-dipole (I-D) Na+ H2O 40-600 kJ/moldipole - dipole (D-D) HCl HCl 5-25 kJ/moldipole - induce dipole (D-ID) HCl O2 2-10 kJ/molLondon Dispersion (LD) N2 N2 0.05 - 40 kJ/mol H-Bond(10-40)kJ/molH-Bond(10-40)kJ/mol-Relative strengthStrongly repulsive at short internuclear distances, very weak at long internuclear distances-Working Range-Very important in protein folding results in a great variety of protein shapes & sizes Properties of SolutionsColligative Properties1. lowering the Vapor Pressure2. Boiling-Point Elevation3. Freezing-Point Depression4. Osmosis Factors Affecting SolubilityDynamic equilibriumFactors Affecting Solubility-The solution processSolvationHydration1. Solute-solute interactions2. Solvent-solvent interactions2. Solute-solvent interactions-Solution FormationEnergy ChangesSpontaneity and Disorder. Processes in which the energy content of the system deceases tend to occur spontaneously. Processes in which the disorder of the system increases tend to occur spontaneously.NH4NO3H=26.4kJ/mol.Substances with similar intermolecular attractive forces tend to be soluble in one another.-“Like dissolves like”-CH2-CH2-C-OHO-CH-CH3CH3Colligative Properties. Differ from those of the pure solvent. Depend primarily on the concentration not the kind of solute particles“Depending on the collection”-The vapor pressure of a liquid is the pressure exerted by its vapor when the liquid and vapor states are in dynamic equilibrium.- A nonvolatile solute reduces the rate of vaporization of the solvent.- The extent to which a nonvolatile solute lowers the vapor pressure is proportional to its concentration.-Boiling point-Liquids boil when the external pressure equals the vapor pressure.-Two ways to get a liquid to boil: increase temperature or decrease pressure.-Normal boiling point is the boiling point at 760 mmHg (1 atm).- Boiling point is dependent on the intermolecular forcesPolar molecules have higher b.p. than nonpolar molecules-Freezing point The freezing point corresponds to the temperature at which the vapor pressures of the solid and liquid phases are the same.The Concentration of Solute ParticlesThe Concentration of Solute Particles# Nonelectrolytes：One mole of a nonelectrolyte produces one mole of solute particlescsolute particles= c# Electrolytes:Exist as ions in solutionProvide more than one mole of particles per mole of solute dissolvedcs.p.=ic, i is the moles of solute particles per mole solute1. Lowering the Vapor PressureDissolved solute lowers vapor pressure of solvent.PA = A PARoaults LawPA: the vapor pressure of the solutionXA: the mole fraction of the solventPA: the vapor pressure of the pure solventIdeal solutions:Real solutions:When the solute concentration is low and when the solute and the solvent are much alike in molecular size and in the strength and type of intermolecular attractions. What you expect for the vapor pressure when the intermolecular forces between solvent and solute are weaker than those between solvent and solvent and between solute and solute. Conversly, what you expect when the interactions between solute and solvent are exceptionally strong?2.Boiling-Point Elevation And3.Freezing-Point DepressionDTb = Kb mDTf = Kf mKb: molal boiling-point elevation constantm- molality: the number of moles of solute per 1000 g of solventKf : molal freezing-point depression constant强电解质的依数性偏差强电解质的依数性偏差(Deviation of Colligative Properties for Strong Electrolytes)电解质稀溶液的依数性电解质稀溶液的依数性:p=iKbBTb=iKbbBTf=iKfbB难挥发的非电解质稀溶液的依数性难挥发的非电解质稀溶液的依数性: p=KbBTb=KbbBTf=KfbB 对对AB型强电解质（型强电解质（NaCl）, i2 A2B型（型（Na2SO4）或）或AB2型（型（ MgCl2） 强电解质，强电解质，i3(近似值近似值).i称校正因子称校正因子Molarity(M)=Amountofsolute (inmoles)Volumeofsolution(inliters)Molality(m)=Amountofsolute (inmoles)Massofsolvent(inkilograms)An antifreeze solution is prepared containing 40.0 g of ethylene glycol (molar mass=62.0 g/mol) in 60.0 g waterCalculate the freezing and boiling points of this solution.Solution:For water, Kf=1.86 and Kb=0.52 Hence the solution should freeze at 20.1 and boil at 105.6.4. OsmosisDiffusionMicrocon Centrifugal Filter Unit超滤膜(ultra-filtration membrane) 透析袋(dialysis tubing)产生渗透条件产生渗透条件: :渗透方向渗透方向： 稀溶液稀溶液 浓溶液浓溶液渗透现象会无止境地进行下去吗渗透现象会无止境地进行下去吗?The net movement of solvent is always toward the more concentrated solution .渗透现象渗透现象半透膜半透膜产生渗透原因产生渗透原因- Osmosis PressureThe Pressure required to prevent osmosis.PV = nRT P = cRTExample: Calculate the osmotic pressure of 0.10 mol/Lglucose solution at 25. How about 0.10 mol/L NaCl solution?Solution:cos(glucose)= cglucose =0.10 mol/L P(glucose) = cosRT=0.10x8.31x298=250 kPacos(NaCl)=i c=2x0.10=0.20 mol/L P(NaCl)=0.20x8.31x298=500 kPaThe unit here is kPa!Jacobus Henricus vant Hoff1852-1911 例：例：25时，求时，求0.9%的生理盐水的渗透压是多少？的生理盐水的渗透压是多少？渗透浓度渗透浓度(Osmolarity)单位:渗透摩尔每升（Osmol/L）或毫渗透摩尔每升（mOsmol)每升溶液中所能产生渗透效应的各物质质点的总浓度正常人血浆总渗透浓度为正常人血浆总渗透浓度为303.7等渗溶液等渗溶液:280-320mOsmol/L低渗溶液低渗溶液:320mOsmol/L临床规定临床规定渗透方向：低渗渗透方向：低渗 高渗高渗- Osmosis and living cellCellular Responds to Body Fluid TonicityCellular Responds to Body Fluid TonicityIsotonicHypertonicHypotonic例例: 1.00 g of heme is dissolved in water and diluted to 100 mL. At 20, the osmotic pressure is measured to be0.366 kPa. Calculate the molar mass of heme. How about the freezing point of the solution?Solution:P=cRT; c=P/(RT)=0.366/(8.81x293)=1.50x10-4 mol/Ln=cV=1.50x10-4x100x10-3=1.50x10-5 molMolar mass=m/n=1.00/1.50x10-5=6.67x104 g/molTf=KfbB=Kfc=1.50x10-4x1.86=2.79x10-4Hence this heme solution should freeze at 0.00 例例: 1.00 g of heme is dissolved in water and diluted to 100 mL. At 20, the osmotic pressure is measured to be0.366 kPa. Calculate the molar mass of heme. How about the freezing point of the solution? (Kf=1.86)Important termsIntermolecular forcesVan der Waals forcesDipole-dipole forcesLondon(dispersion) forcesHydrogen bondingColligative propertiesVapor-pressure-loweringBoiling-point elevationFreezing-point depressionOsmosisOsmotic pressureReviewAtom MoleculeSubstancesIMFOrientation ForceInduction ForceLondon Dispersion ForceH-BondingIon-Dipole ForcesHydrophobic InteractionsSolubilityColligative propertiesIncreased EntropyMolecular polarizationSummary of conceptsSummary of conceptsSkills1.Identifyingintermolecularforces2.Determiningtheboilingpointsonthebasisofintermolecularforces3.Calculatingosmoticpressure,boiling-pointelevationandfreezing-pointdepression.Questions 习题P193: 4,6,8,12,14P168: 7,8,10,15THE END