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Gaya Antar Molekul
 

Gaya Antar Molekul

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  • Mon Start 1110
  • Start Wed 1210
  • CH 4 , methane, is the only nonpolar substance so only has London forces. HF and CH 3 OH are both polar molecules and have hydrogen bonds.
  • Jangan menyerah dalam belajar kimia..selalu ada hasil yang baik dan akan ada harga yang di bayar untuk ingin berhasil.. 
  • Molecular mass, strength of intermolecular forces and the external pressure on the material all effect the boiling point of a substance.
  • 06/26/13 Safety Dog Productions Chem FAQ: How can I determine what phase will be present at a given pressure and temperature using a phase diagram?
  • At 89 °C and 760 mmHg we are in the liquid range—above the line BD for gases.
  • Fig 12.37, 38, 39
  • Start Tues

Gaya Antar Molekul Gaya Antar Molekul Presentation Transcript

  • Chapter 12:Intermolecular Attractionsand the Properties of Liquidsand SolidsChemistry: The MolecularNature of Matter, 6EJespersen/Brady/Hyslop
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 2Chapter 12 Intermolecular Forces Important differences between gases,solids, and liquids: Gases Expand to fill their container Liquids Retain volume, but not shape Solids Retain volume and shape
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 3Chapter 12 Intermolecular Forces Physical State of molecule dependson Average kinetic energy of particles Recall KE ∝ Tave Intermolecular Forces Energy of Inter-particle attraction Physical Properties of Gases, Liquidsand Solids determined by How tightly molecules are packed together Strength of attractions betweenmolecules
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 4 Converting gas → liquid or solid Molecules must get closer together Cool or compress Converting liquid or solid → gas Requires molecules to move farther apart Heat or reduce pressure As T↓, Kinetic Energy of molecules ↓ At certain T, molecules don’t haveenough energy to break away from oneanother’s attractionIntermolecular Attractions
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 5Inter vs. Intra-Molecular Forces Intramolecular forces Covalent bonds within molecule Strong ∆Hbond (HCl) = 431 kJ/mol Intermolecular forces Attraction forces between molecules Weak ∆Hvaporization (HCl) = 16 kJ/molCl H Cl HCovalent Bond (strong) Intermolecular attraction (weak)
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 6Electronegativity ReviewElectronegativity: Measure of attractiveforce that one atom in a covalent bond has forelectrons of the bond
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 7Bond Dipoles Two atoms with different electronegativityvalues share electrons unequally Electron density is uneven Higher charge concentration around moreelectronegative atom Bond dipoles Indicated with delta (δ) notation Indicates partial charge has arisenH Fδ+δ−
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 8Net Dipoles Symmetrical molecules Even if they have polar bonds Are non-polar because bond dipoles cancel Asymmetrical molecules Are polar because bond dipoles do not cancel These molecules have permanent, net dipoles Molecular dipoles Cause molecules to interact Decreased distance between molecules increasesamount of interaction
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 9Intermolecular Forces When substance melts or boils Intermolecular forces are broken Not covalent bonds Responsible for non-ideal behavior ofgases Responsible for existence of condensedstates of matter Responsible for bulk properties of matter Boiling Points and Melting Points Reflect strength of intermolecular forces
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 10Three Important Types ofIntermolecular Forces1. Dipole-dipole forces Hydrogen bonds2. London dispersion forces3. Ion-dipole forces Ion-induced dipole forces
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 11I. Dipole-dipole Attractions Occur only between polarmolecules Possess dipole moments Molecules need to beclose together Polar molecules tend toalign their partial charges + to – As dipole moment ↑,intermolecular force ↑+ − + −− + − ++ − + −
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 12I. Dipole-dipole Attractions Tumbling molecules Mixture of attractive andrepulsive dipole-dipoleforces Attractions (- -) greaterthan repulsions(- -) Get net attraction ~ 1% of covalent bond
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 13Dipole - Dipole Attractions Interactions between net dipoles in polarmolecules About 1% as strong as a covalent bond Decrease as molecular distance increases Drops off as 1/d3(d = distance betweendipoles) Dipole-dipole forces ↑ with ↑ polarity
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 14Hydrogen Bonds Special type of Dipole-Dipole Interaction Very strong dipole-dipole attraction ~40 kJ/mol Occurs between H and highly electronegative atom(O, N, or F) H—F, H—O, and H—N bonds very polar e−s lie closer to X than to H, so high partial charges H only has 1 e−, so δ+H presents almost bare proton δ−X almostfull −1 charge Element’s small size, means high charge density Positive end of one can get very close to negative end ofanother
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 15Examples of Hydrogen BondingH OHH OHH OHH NHHH F H OHH F H NHHH NHHH NHHH NHHH OH
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 16Effects of Hydrogen Bonding Boiling points of Hcompounds ofelements of GroupsIVA, VA, VIA, andVIIA. Boiling points ofmolecules with Hbonding are higherthan expected. Don’t follow rule thatBP ↑ as MM ↑(London forces ↑)BoilingPoint(°C)
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 17Hydrogen Bonding in Water Responsible for expansion of water as it freezes Hydrogen bonding produces strong attractions inliquid Hydrogen bonding (dotted lines) betweenwater molecules in ice form tetrahedral configuration
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 18II. London Dispersion Forces Intermolecular forces betweennonpolar molecules Two neutral molecules (atoms)can affect each other Nucleus of 1 molecule (atom)attracts e−’s of adjacent molecule(atom) Electron cloud distorts Temporary or instantaneousdipole forms One instantaneous dipole caninduce another in adjacent molecule(atom) Results in net attractive forcee−e−2+e−e−ElectrostaticattractionHe atom 1 He atom 22+δ−δ−δ+δ+
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 19London Forces When atoms near one another,their valence electrons interact Repulsion causes electronclouds in each to distort andpolarize Instantaneous, induceddipoles result from thisdistortion Effect enhanced with increasedparticle mass Effect diminished by increaseddistance between particles
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 20London Dispersion Forces Instantaneous dipole-induced dipoleattractions London Dispersion Forces London forces Dispersion forces Decrease as 1/d6(d = distance betweenmolecules) Operate between all molecules Neutral or net charged Nonpolar or polar
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 21London Dispersion Forces Ease with which dipole moments can beinduced and thus London DispersionForces depends on1. Polarizability2. Molecular size Number atoms Molecular mass1. Molecular Shape
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 221. Polarizability Ease with which electrondistribution in neutral atom(or molecule) can be distorted Larger molecules = more polarizable Larger number of e−s ∝ greater ease ofdistorting electron cloud Magnitude of resulting partial charge is larger London Forces ↑ as MM ↑ More e−, less tightly held London Forces ↑ as electron cloud volume ↑ Depends on size of atoms
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6EYour Turn!List all intermolecular forces for CH3CH2OH.A. H-bondingB. H-bonding, Dipole-Dipole, LondonC. Dipole-DipoleD. LondonE. London, H-bonding23
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 24Table 12.1 Boiling Points ofHalogens and Noble GasesLarger molecules have stronger London forcesand thus higher boiling points.
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 252. Number of Atoms in Molecule London forces depend on number atoms inmolecule Boiling point of hydrocarbons demonstrates thistrendFormula BP at 1 atm, °C Formula BP at 1 atm, °CCH4 −161.5 C5H12 36.1C2H6 −88.6 C6H14 68.7C3H8 −42.1 : :C4H10 −0.5 C22H46 327
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 26How Intermolecular ForcesDetermine Physical PropertiesPropane, C3H8BP –42.1oCHexane, C6H14 BP 68.7oC More sites (marked with *) along its chain whereattraction to other molecules can occur
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 273. Molecular Shape Increased surface area available for contact= Increased London Forces London dispersion forces betweenspherical molecules are lower thanchain-like molecules More compact molecules H’s not as free to interact with H’s on othermolecules Less compact molecules H’s have more chance to interact with H’son other molecules
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 28Physical Origin of Shape Effect Small area forinteraction Larger area forinteractionMore compact – lower BP Less compact – higher BP
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6EYour Turn!Which species has a higher boiling point, Cl2 orHCl; F2 or HF ?A. HCl; F2B. Cl2; F2C. HCl; HFD. Cl2 ; HF29
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 30III. Ion-dipole Attractions Attractions between ion and charged end ofpolar molecules Attractions can be quite strong as ions have fullcharges(a) Negative ends of water dipoles surround cation(b) Positive ends of water dipoles surround anion
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 31Ex. Ion-dipole AttractionsAlCl3·6H2O Positive charge of Al3+ionattracts partial negativecharges δ–on O of watermolecules Ion-dipole attractions holdwater molecules to metalion in hydrate Water molecules are foundat vertices of octahedronaround aluminum ion Attractions between ion and polar molecules
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 32Ion-induced Dipole Attractions Attractions between ion and dipole it induceson neighboring molecules Depends on Ion charge and Polarizability of its neighbor Attractions can be quite strong as ion charge doesNOT flicker on and off like instantaneous dipoles ofordinary London forces Ex. I–and Benzene
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 33Summary of IntermolecularAttractionsDipole-dipole occur between neutral molecules with permanentdipoles; about 1% - 5% of covalent bond Mid range in terms of intermolecular forcesHydrogen bonding Special type of dipole-dipole interaction Occur when molecules contain N—H,H—F and O—H bonds About 5% to 10% of a covalent bond
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 34Summary of IntermolecularAttractionsLondon dispersion Present in all substances Weakest intermolecular forces Weak, but can lead to large net attractionsIon-dipole Occur when ions interact with polar molecules Strongest intermolecular attractionIon-induced dipole Occur when ion induces dipole on neighboring particle Depend on ion charge and polarizability of its neighbor
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 35Using Intermolecular Forces Often can predict physical properties (like BPand MP) by comparing strengths ofintermolecular attractions Ion-Dipole Hydrogen Bonding Dipole-Dipole London Dispersion Forces Larger, longer, heavier molecules have strongerIMFs Smaller, more compact, lighter molecules haveweaker IMFsWeakestStrongest
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 36Learning Check Identify the kinds of intermolecular forces present inthe following compounds Rank them in order of increasing boiling point: H2S,CH3OH, CBr4, and NeHSHHCO HHHBrCBrBrBrNedipole-dipoleHydrogenbondingLondonforcesLondonforcesMM=331.6MM=20.2CH3OH >H2S > CBr4 > Ne
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 37Physical Properties that Depend onHow Tightly Molecules Pack Compressibility Measure of ability of substance to be forced intosmaller volume Determined by strength of intermolecular forces Gases highly compressible Molecules far apart Weak intermolecular forces Solids and liquids nearly incompressible Molecules very close together Stronger intermolecular forces
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 38Intermolecular Forces DetermineStrength of Many PhysicalProperties Retention of Volume and Shape Solids keep both volume and shape Strongest intermolecular attractions Molecules closest Gases, keep nothing Weakest intermolecular attractions Molecules farthest apart Liquids keep volume, but not shape Attractions intermediate
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 39Diffusion Movement thatspreads one gasthough another gas tooccupy spaceuniformly Spontaneousintermingling ofmolecules of one gaswith molecules ofanother gasOccurs more rapidly in gases than in liquidsHardly at all in solids
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 40Diffusion In Gases Molecules travel longdistances betweencollisions Diffusion rapid In Liquids Molecules closer Encounter morecollisions Takes a long time tomove from place toplace In Solids Diffusion nonexistent atroom temp Will ↑ at high Temp
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 41Surface Tension Why does H2O bead upon a freshly waxed carinstead of forming alayer? Inside body of liquid Intermolecular forces inall directions Molecules at surface IMF only pull down andto side Fewer attractions, sofree to expand indirection with no forces
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 42Surface Tension Tendency of liquidto take shape thatminimizes surfacearea Molecules at surfacehave higher potentialenergy than those inbulk of liquid Energy required toexpand or increasesurface by unit area Wax = nonpolar H2O = polar Water beads aswants to maximizeattractions
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 43Surface Tension Liquids containingmolecules with strongintermolecular forces havehigh surface tension Allows us to fill glass aboverim Gives surface roundedappearance Surface acts as “skin” that letswater pile up Surface resists expansion andpushes back Surface Tension ↑as IMF ↑ Surface Tension ↓as IMF ↓
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 44Wetting Ability of liquid to spreadacross surface to formthin film Greater similarity inattractive forcesbetween liquid andsurface, yields greaterwetting effect Occurs only ifintermolecular attractiveforce between surfaceand liquid about asstrong as within liquiditself
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 45WettingEx. H2O wets clean glass surface as it forms Hbonds to SiO2 surface Does not wet greasy glass, as grease interactsweakly with water Only London dispersion forces Forms bead insteadSurfactants Added to detergents to lower surface tension of H2O Now water can get better access to surface to becleaned
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 46Surfactants Substances that have polar and non-polarcharacteristics Long chain hydrocarbons with polar tailOSOO−Na+OOO−Na+ Nonpolar end interacts with grease Polar end interacts with H2O Thus increasing solubility of grease in water
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 47Viscosity Resistance to flow Measure of fluid’sresistance to flow orchanging form Larger moleculescollide and interactmore often, impedingtheir flow Also called internal friction Depends on intermolecular attractions Molecular shapewww.chemistryexplained.com
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 48Viscosity Viscosity ↓ when Temperature ↑ Most people associate liquids with viscosity Molasses more viscous than water Gases have viscosity Respond almost instantly to form-changing forces Solids, such as rocks Normally respond very slowly to forces acting tochange their shape For same size molecules, viscosityincreases as strength of IntermolecularForces increases
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 49Effect of Intermolecular Forces onViscosityAcetone Polar molecule Dipole-dipole and London forcesEthylene glycol Polar molecule Hydrogen-bonding Dipole-dipole and London forcesWhich is more viscous??
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6EYour Turn!For each pair given, which is more viscose ? CH3CH2CH2CH2OH, CH3CH2CH2CHO; C6H14, C12H26; NH3(l ), PH3(l )A. CH3CH2CH2CH2OH; C6H14; NH3(l )B. CH3CH2CH2CH2OH; C12H26; NH3(l )C. CH3CH2CH2CHO; C6H14; PH3(l )D. CH3CH2CH2CHO; C12H26; NH3(l )E. CH3CH2CH2CH2OH; C12H26; PH3(l )50
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 51Solubility “Like dissolves like” To dissolve polar substance, use polar solvent To dissolve nonpolar substance, use nonpolarsolvent Compare relative polarity of two substances Similar polarity means greater ability to interactwith each other Differing polarity means that they don’t interact;move past each other Surfactants Both polar and non-polar characteristics Used to increase solubility
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 52Your Turn!Which of the following are not expectedto be soluble in water?A. HFB. CH4C. CH3OHD. All are soluble
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 53Phase Changes Changes of physical state Deal with motion of molecules As temperature changes Matter will undergo phase changes Liquid → Gas Evaporation As heat H2O, forms steam or water vapor Requires energy or source of heat to occur
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 54Phase Changes Solid → Gas Sublimation Ice cubes in freezer, leave in long enough disappear Endothermic Gas → Liquid Cooling or Condensation Dew is H2O vapor condensing onto cooler ground Exothermic
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 55Rate of Evaporation Depends on Temperature Surface area Strength ofintermolecularattractions Molecules that escapefrom liquid have largerthan average KE’s When they leave Average KE ofremainingmolecules is less T lower
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 56Effect of Temperature onEvaporation Rate For given liquid Rate of evaporation perunit surface area ↑as T ↑ Why? At higher T, totalfraction of moleculeswith KE large enough toescape is larger Result: rate ofevaporation is larger
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 57Kinetic Energy Distribution in TwoDifferent Liquids Smaller IMF’s Lower KE required toescape liquid A evaporates faster Larger IMF’s Higher KE requiredto escape liquid B evaporatesslowerA B
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 58Changes Of State Involve Equilibria Fraction of molecules in condensed state ishigher when intermolecular attractions arehigher Intermolecular attractions must be overcometo separate the particles, while separatedparticles are simultaneously attracted to oneanothercondensedphaseseparatedphase
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 59Before System ReachesEquilibrium Liquid is placed inempty container Begins to evaporate Once in gas phase Molecules cancondense by Striking surface of liquidand giving up somekinetic energy
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 60System At Equilibrium Rate of evaporation =rate of condensation Can occur in systemwhere molecules areconstrained to remainclose to liquid surface
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 61Similar Equilibria Reached inMeltingMelting Point (mp) Solid begins to changeinto liquid as heat added Dynamic Equilibriaexists between solid andliquid states Melting (red arrows) andfreezing (black arrows)occur at same rate As long as no heat added orremoved from equilibriummixture
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 62Equilibria Reached inSublimationAt equilibrium Molecules evaporatefrom solid at samerate as moleculescondense from vapor Molecules sublimeand condense oncrystal at same rate
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 63Phase ChangesEnergyofSystemGasSolidLiquidMeltingor FusionVaporization CondensationFreezingSublimationDeposition↓ Exothermic, releases heat↑ Endothermic, absorbs heat
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 64Energy Changes AccompanyingPhase Changes All phase changes are possible under theright conditions Following sequence is endothermicheat solid → melt → heat liquid → boil → heat gas Following sequence is exothermiccool gas → condense → cool liquid → freeze → coolsolid
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 65∆H Accompanying PhaseChangesEndothermic Phase Changes1. Must Add Heat2. Energy entering system (+)Sublimation: ∆Hsub > 0Vaporization: ∆Hvap > 0Melting or Fusion: ∆Hfus > 0Exothermic Phase Changes1. Must Give Off Heat2. Energy leaving system (–)Deposition: ∆H < 0 = − ∆HsubCondensation: ∆H < 0 = − ∆HvapFreezing: ∆H < 0 = − ∆Hfus
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 66Phase Changes As T changes, matter undergoes phasechanges Phase Change Transformation from one phase to another Liquid-Vapor Equilibrium Molecules in liquid Not in rigid lattice In constant motion Denser than gas, so more collisions Some have enough kinetic energy toescape, some don’t
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 67Liquid-Vapor Equilibrium At any given T, Average KineticEnergy of moleculesis constant But have distributionKEs of particles Certain number ofmolecules haveenough KE toescape surface Process is Evaporation or Vaporization As T ↑, Avg. KE ↑ and numbermolecules with enough KE to escape ↑Kinetic EnergyFractionofmolecules
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 68Vapor Pressure (VP) Pressure molecules exert when they evaporate orescape into gas (vapor) phase Pressure of gas when liquid or solid is atequilibrium with its gas phase Increasing temperature increases vapor pressurebecause conversion is endothermic liquid + heat of vaporization ↔ gasEquilibrium Vapor Pressure VP once dynamic equilibrium reached Usually referred to as simply vapor pressure
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 69Measuring Vapor PressureTo measure pressures inside vessels, a manometer isused.
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 70Vapor Pressure Diagram Variation ofvapor pressurewith T Ether Volatile High vaporpressure near RT Propyleneglycol Non-volatile Low vaporpressure nearRTRT = 25 °C
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 71Effect of Volume on VPA. Initial V Liquid – vaporequilibrium existsΑ. ↑ V P ↓ Rate ofcondensation ↓A. More liquidevaporates New equilibriumestablished
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 72Measuring ∆Hvap Clausis-Clayperon Equation Measure P at various Ts, then plot Two point form of Clausis-Clayperon Equation Measure P at two T’s and solve equationCTRHPvap+ ∆−=1ln−∆=1221 11lnTTRHPP vap
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 73Learning CheckThe vapor pressure of diethyl ether is 401 mmHg at18°C, and its molar heat of vaporization is 26 kJ/mol.Calculate its vapor pressure at 32°C.4928.015.291115.3051)/(314.8/106.2ln421−=−⋅×=KKmolKJmolJPP−∆=1221 11lnTTRHPP vap6109.04928.021== −ePP216109.0PP=mmHgmmHgP 22 106.66109.0401×==T1 = 273.15 + 18 = 291.15KT2 = 273.15 + 32 = 305.15K
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6EYour Turn!Determine the enthalpy of vaporization, inkJ/mol, for benzene, using the following vaporpressure data. T = 60.6 C; P = 400 torr T = 80.1 C; P = 760 torrA. 32.2 kJ/molB. 14.0 kJ/molC. -32.4 kJ/molD. 0.32 kJ/molE. -14.0 kJ/mol74
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6EYour Turn! - Solution7512 2 11 1ln400 Hg 1 1lnJ760 Hg 353.1 K 333.6 K8.314K mol32,235 J/mol or 32.2 kJ/molvapvapvapHPP R T THmmmmH∆  = − ÷ ∆  = − ÷ ∆ =
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 76Do Solids Have Vapor Pressures? Yes At given T Some solid particles have enough KE so escapeinto vapor phase When vapor particles collide with surface they can be captured Equilibrium vapor pressure of solid P of vapor in equilibrium with solid
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 77Boiling Point (bp) T at which vapor pressure of liquid =atmospheric pressure. Bp ↑ as strength of IMF ↑Normal boiling point T at which vapor pressure = 1 atm
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 78Effects of Hydrogen Bonding Boiling points of Hcompounds ofelements of GroupsIVA, VA, VIA, and VIIA. Boiling points ofmolecules with Hbonding are higher thanexpected Don’t follow rule thatBP ↑ as MM ↑ (Londonforces ↑)
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 79Your Turn!Which of the following will affect the boilingpoint of a substance?A.Molecular mass of the materialB.Intermolecular attractionsC.The external pressure on the materialD.All of theseE.None of these
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 80Heating Curve Heat added at constant rate Diagonal linesHeating of solid, liquid or gas Horizontal linesPhase changesMelting pointBoiling point
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 81Cooling Curve Heat removed at constant rate Diagonal linesCooling of solid,liquid or gas Horizontal linesPhase changesMelting pointBoiling point SupercoolingT of liquid dips below its freezing point
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6EYour Turn! How much heat, in J, is required to convert10.00 g of ice at -10.00 oC to water at50.00 oC ? Specific heat (J/g K): ice, 2.108, water, 1.487 Enthalpy of fusion = 6.010 kJ/mol54A. 5483 JB. 5643 JC. 2304 JD. 2364 JE. 62,400 J82
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 83Energies of Phase Changes Expressed per mole Molar heat of fusion (∆Hfus) heat absorbed by 1 mole of solid when it melts to giveliquid at same T and P Molar heat of vaporization (∆Hvap ) heat absorbed when 1 mole of liquid is changed to 1 moleof vapor at constant T and P Molar heat of sublimation (∆Hsub ) Heat absorbed by 1 mole of solid when it sublimes to give 1mole of vapor at constant T and P All of these quantities tend to ↑ with ↑ingintermolecular forces
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 84Le Chatelier’s Principle Equilibria are often disturbed or upset When dynamic equilibrium of system is upsetby a disturbance System responds in direction that tends tocounteract disturbance and, if possible, restoreequilibrium Position of equilibrium used to refer to relative amounts of substance oneach side of double (equilibrium) arrows
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 85Liquid Vapor EquilibriumLiquid + Heat  Vapor ↑ing T ↑s amount of vapor ↓s amount of liquid Equilibrium has shifted = right shift more vapor is produced at expense of liquid Temperature-pressure relationships can berepresented using a phase diagram
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 86Phase Diagrams Show the effects of both pressure and temperatureon phase changes Boundaries between phases indicate equilibrium Triple point: the temperature and pressure at which s, l, and g are allat equilibrium Critical point: the temperature and pressure at which a gas can nolonger be condensed TC=temperature at critical point PC = pressure at critical point
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 87Phase Diagram  X axis = temperature Y axis = pressure As P ↑ (T const), solidmost likely More compact As T ↑(P const), gasmost likely Higher energy Each point = T and P B = E = F =E0.01°C, 4.58 torr100°C, 760 torr–10°C, 2.15 torrF
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 88Phase Diagram of Water AB = vapor pressurecurve for ice BD = vapor pressurecurve for liquid water BC = melting point line B = triple point = Twhere all 3 phases inequilibrium D = critical point T and P above whichliquid does not exist
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 89Case Study: An Ice Necklace A cube of ice may besuspended on a string simplyby pressing the string into theice cube. As the string ispressed onto the surface, itbecomes embedded into theice. Why does this happen?
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 90Phase Diagram – CO2 Now linebetween solidand liquidslants to right More typical Where is Triplepoint? Where isCritical point?
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 91Supercritical Fluid Substance with temperature above its criticaltemperature (TC) and density near its liquiddensity Have unique properties that make themexcellent solvents Values of TC tend to ↑ with increasedintermolecular attractions between particles
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 92Your Turn!At 89 °C and 760 mmHg,what physical state ispresent?A.SolidB.LiquidC.GasD.Supercritical fluidE.Not enoughinformation is given
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 93Types of Solids Crystalline Solids Solids with highly regular arrangements ofcomponents Amorphous Solids Solids with considerable disorder in theirstructures
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 94Crystalline Solids Unit Cell Smallestsegment thatrepeatsregularly Smallestrepeating unit oflattice 2-DimensionalUnit Cells
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 95Crystal Structures HaveRegular Patterns Lattice Many repeats of unit cell Regular, highlysymmetrical system Three (3) dimensionalsystem of pointsdesignating positions ofcomponents Atoms Ions Molecules
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 96Three Types Of 3-D Unit Cells Simple cubic Has one host atom at each corner Edge length a = 2r where r is radius of atom or ion Body-centered cubic (BCC) Has one atom at each corner and one incenter Edge length Face-centered cubic (FCC) Has one atom centered in each face, andone at each corner Edge length r22a =3r4a =
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 97Close Packing of Spheres1stlayer 2ndlayer Most efficient arrangement of spheres in 2-D Each sphere has 6 nearest neighbors Square lattice: 2-dimensional arrays
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 98Two Ways to Put on 3rdLayer1. Directly abovespheres in 1stlayer2. Above holes in 1stlayer Remaining holes notcovered by 2ndlayerCubic lattice: 3-dimensional arrays
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 993-D Simple Cubic LatticePortion of lattice—open viewUnit CellSpace fillingmodel
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6EOther Cubic Lattices100Face CenteredCubicBody CenteredCubic
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 101Ionic SolidsLattices of Alternating charges Want cations next to anions Maximizes electrostatic attractive forces Minimizes electrostatic repulsions Based on one of three basic lattices: Simple cubic Face centered cubic Body centered cubic
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6ECommon Ionic SolidsRock salt or NaCl Face centered cubic lattice of Cl ions (green) Na+ions (blue) in all octahedral holes102
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 103Other Common Ionic SolidsCesiumChloride,CsClZinc Sulfide,ZnSCalciumFluoride,CaF2
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 104Spaces In Ionic Solids Are FilledWith Counter Ions In NaCl Cl−ions form face-centered cubic unitcell Smaller Na+ions fillspaces between Cl−ions Count atoms in unitcell Have 6 of each or1:1 Na+:Cl−ratio
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 105Counting Atoms per Unit Cell 4 types of sites in unit cell Central or body position – atom is completely containedin one unit cell Face site – atom on face shared by two unit cells Edge site – atom on edge shared by four unit cells Corner site – atom on corner shared by eight unit cellsSite Counts as Shared by X unit cellsBody 1 1Face 1/2 2Edge 1/4 4Corner 1/8 8
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 106Example: NaClSite # of Na+# of Cl−Body 1 0Face 0Edge 0Corner 0Total 4 4( ) 36 21 =×( ) 312 41 =×( ) 18 81 =×FaceEdge CornerCenter
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 107Learning Check:1:1CsClDetermine the number of each type of ion inthe unit cell.4:4ZnS4:8CaF2
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 108Some Factors AffectingCrystalline Structure Size of atoms or ions involved Stoichiometry of salt Materials involved Some substances do not form crystalline solids
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 109Amorphous Solids (Glass) Have little order, thus referred to as “supercooled liquids” Edges are not clean, but ragged due to the lackof order
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 110X-Ray Crystallography X-rays are passed throughcrystalline solid Some x-rays are absorbed,most re-emitted in alldirections Some emissions by atomsare in phase, others out ofphase Emission is recorded on film
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 111X-ray DiffractionExperimental Setup Diffraction Pattern
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 112Interpreting Diffraction Data As x-rays hitatoms in latticethey are deflected Angles ofdeflections relatedto lattice spacing So we canestimate atomicand ionic radiifrom distance data
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 113Interpreting Diffraction DataBragg Equation nλ=2dsinθ n = integer (1, 2, …) λ = wavelength ofX–rays d = interplanespacing in crystal θ = angle ofincidence and angleof reflectance ofX–rays to variouscrystal planes
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 114Ex. 2 Diffraction DataThe diffraction pattern of copper metal wasmeasured with x-ray radiation of wavelength of1.315 Å. The first order (n=1) Bragg diffractionpeak was found at an angle theta of 50.5degrees. Calculate the spacing between thediffracting planes in the copper metal.1(1.315 Ǻ)=2×d×sin(50.5°)nλ = 2dsinθd = 2.83 Ǻ
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 115Ex 3. Using Diffraction dataX-ray diffraction measurements reveal thatcopper crystallizes with a face-centered cubiclattice in which the unit cell length is 3.62 Å.What is the radius of a copper atom expressedin angstroms and in picometers?This is basically a geometry problem.
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 116Ex.3 (cont)A12.5)A62.3(2diagonal =×=diagonal = 4 × rCu = 5.12 ÅrCu = 1.28 ÅNow convert to pmRecall 1 Å = 1 × 10−10m and 1 pm = 1 × 10−12mpmmpmAmA 128101110128.1 1210=×××× −−Pythagorean theorem: a2+ b2= c2Where a = b = 3.62 Å sides and c = diagonal2a2= c2and aac 22 2==
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 117Learning CheckSilver packs together in a faced center cubicfashion. The interplanar distance, d,corresponds to the length of a side of the unitcell, and is 4.07 angstroms. What is the radiusof a silver atom?ra 22=r22A07.4 =r = 0.536 Åa
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 118Ionic Crystals (ex. NaCl,NaNO3) Have cations and anions at lattice sites Are relatively hard Have high melting points Are brittle Have strong attractive forces between ions Do not conduct electricity in their solidstates Conduct electricity well when molten
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6ESample Homework Problem Potassium chloride crystallizes with the rocksalt structure. When bathed in X-rays, thelayers of atoms corresponding to thesurfaces of the unit cell produce a diffractedbeam of X-rays (λ=154 pm) at an angle of6.97º. From this, calculate the density(g/cm3).119
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6EYour Turn!Yitterbium crystallizes with a face centeredcubic lattice. The atomic radius of Yitterbiumis 175 pm. Determine the unit cell length.A. 495 pmB. 700 pmC. 350 pmD. 990 pmE. 247 pm120
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6EYour Turn! - Solution121diagonal of cube = 4 where = atomic radiusdiagonal of cube = 2 a where a = side of cube4 4 x 175 pma = 495 pm2 2r rr= =
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 122Covalent Crystals Lattice positions occupied by atoms that arecovalently bonded to other atoms atneighboring lattice sites Also called network solids Interlocking network of covalent bonds extendingall directions Covalent crystals tend to be very hard have very high melting points have strong attractions betweencovalently bonded atoms
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 123Ex. Covalent (Network) Solid Diamond (all C) shown SiO2 silicon oxide Alternating Si and O Basis of glass and quartz Silicon carbide (SiC)
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 124Metallic Crystals Simplest models Lattice positions of metalliccrystal occupied by positiveions Cations surrounded by “cloud”of electrons formed by valence electrons extends throughout entire solid
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E 125Metallic Crystals Conduct heat and electricity By their movement, electrons transmit kineticenergy rapidly through solid Have the luster characteristically associatedwith metals When light shines on metal Loosely held electrons vibrate easily Re-emit light with essentially same frequencyand intensity
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6E126Learning Check:Substance ionic molecular covalent metallicX: pulverizes when struck;non-conductive of heatand electricityY: White crystalline solidthat conducts electricalcurrent when molten ordissolvedZ: shiny, conductive,malleable with highmelting temperatureClassify the following in terms of most likely type of solid.
  • Jespersen/Brady/Hyslop Chemistry: The Molecular Nature of Matter, 6EYour Turn!Molecular crystals can contain all of the listedattraction forces except:A. Dipole-dipole attractionsB. Electrostatic forcesC. London forcesD. Hydrogen bonding127