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CHAPTER 11 INTERMOLECULAR FORCES

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Information about CHAPTER 11 INTERMOLECULAR FORCES
Science-Technology

Published on December 4, 2008

Author: aSGuest5273

Source: authorstream.com

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Slide 1: 1 Why is this needle floating? Slide 2: 2 Intermolecular Forces: (inter = between) between molecules What determines if a substance is a solid, liquid, or gas? and the temperature (kinetic energy) of the molecules. Slide 3: 3 Slide 4: 4 Gases: The average kinetic energy of the gas molecules is much larger than the average energy of the attractions between them. Liquids: the intermolecular attractive forces are strong enough to hold the molecules close together, but without much order. Solids: the intermolecular attractive forces are strong enough to lock molecules in place (high order). Are they temperature dependent? Slide 5: 5 The strengths of intermolecular forces are generally weaker than either ionic or covalent bonds. 16 kJ/mol (to separate molecules) 431 kJ/mol (to break bond) + + - - Slide 6: 6 Types of intermolecular forces (between neutral molecules): Dipole-dipole forces: (polar molecules) S O O .. : : .. .. : + - - S O O .. : : .. .. : + - - dipole-dipole attraction What effect does this attraction have on the boiling point? Slide 7: 7 Polar molecules have dipole-dipole attractions for one another. +HCl----- +HCl- dipole-dipole attraction Slide 8: 8 Types of intermolecular forces (between neutral molecules): Hydrogen bonding: cases of very strong dipole-dipole interaction (bonds involving H-F, H-O, and H-N are most important cases). +H-F- --- +H-F- Hydrogen bonding Slide 9: 9 Hydrogen bonding is a weak to moderate attractive force that exists between a hydrogen atom covalently bonded to a very small and highly electronegative atom and a lone pair of electrons on another small, electronegative atom (F, O, or N). Slide 10: 10 Slide 11: 11 Predict a trend for: NH3, PH3, AsH3, and SbH3 Boiling points versus molecular mass 100 0 -100 Slide 12: 12 Predict a trend for: NH3, PH3, AsH3, and SbH3 NH3 PH3 AsH3 SbH3 Slide 13: 13 NH3 PH3 AsH3 SbH3 Now let’s look at HF, HCl, HBr, and HI HF HCl HBr HI Slide 14: 14 Types of intermolecular forces (between neutral molecules): “electrons are shifted to overload one side of an atom or molecule”. London dispersion forces: (instantaneous dipole moment) ( also referred to as van der Waal’s forces) + + - - attraction Slide 15: 15 polarizability: the ease with which an atom or molecule can be distorted to have an instantaneous dipole. “squashiness” In general big molecules are more easily polarized than little ones. little Big and “squashy” Slide 16: 16 Which one(s) of the above are most polarizable? Hint: look at the relative sizes. Slide 17: 17 Slide 18: 18 Other types of forces holding solids together: ionic: “charged ions stuck together by their charges” There are no individual molecules here. Slide 19: 19 Metallic bonding: “sea of electrons” Copper wire: What keeps the atoms together? Cu atoms an outer shell electron To which nucleus does the electron belong? Slide 20: 20 Metallic Bonding: “sea of e-’s” Slide 21: 21 Covalent Network: (diamonds, quartz) very strong. 1.54 Å 3.35 Å 1.42 Å What type of hybridization is present in each? Slide 22: 22 Slide 23: 23 Slide 24: 24 Pentane isomers: C5H12 iso-pentane n-pentane neo-pentane Hvap=25.8 kJ/mol Hvap=24.7 kJ/mol Hvap=22.8 kJ/mol London and “Tangling” All three have the same formula C5H12 Why do they have different enthalpies of vaporization? Slide 25: 25 n-pentane C-C-C-C C iso-pentane C C-C-C C neo-pentane London and “Tangling” Hvap=25.8 kJ/mol Hvap=24.7 kJ/mol Hvap=22.8 kJ/mol Slide 26: 26 Structure effects on boiling points Slide 27: 27 Ion-dipole interactions: such as a salt dissolved in water polar molecule cation anion Slide 28: 28 Slide 29: 29 Phase changes: solid  liquid (melting  freezing) liquid  gas (vaporizing  condensing) solid  gas (sublimation  deposition) Slide 30: 30 Energy changes accompanying phase changes Slide 31: 31 Heating curve for 1 gram of water Slide 32: 32 Heating curve for 1 gram of water Hfus=334 J/g Specific Heat of ice = 2.09 J/g•K Specific Heat of water = 4.184 J/g•K Hvap=2260 J/g Specific Ht. Steam = 1.84 J/g•K Slide 33: 33 Calculate the enthalpy change upon converting 1 mole of water from ice at -12oC to steam at 115oC. solid -12oC solid 0oC liquid 0oC liquid 100oC gas 100oC gas 115oC H1 + H2 + H3 + H4 + H5 = Htotal Sp. Ht. + Hfusion + Sp. Ht. + HVaporization + Sp. Ht. = Htotal Specific Heat of ice = 2.09 J/g•K Hfus=334 J/g Specific Heat of water = 4.184 J/g•K Specific Ht. Steam = 1.84 J/g•K Hvap=2260 J/g Slide 34: 34 Calculate the enthalpy change upon converting 1 mole of water from ice at -12oC to steam at 115oC. solid -12oC solid 0oC liquid 0oC liquid 100oC gas 100oc gas 115oc H1 + H2 + H3 + H4 + H5 = Htotal Sp. Ht. + Hfusion + Sp. Ht. + HVaporization + Sp. Ht. = Htotal Specific Heat of ice = 2.09 J/g•K Hfus=334 J/g Specific Heat of water = 4.184 J/g•K Specific Ht. Steam = 1.84 J/g•K Slide 35: 35 Vapor pressure Slide 36: 36 VAPOR PRESSURE CURVES A liquid boils when its vapor pressure =‘s the external pressure. Slide 37: 37 normal boiling point is the temperature at which a liquid boils under one atm of pressure. liquid pressure = 1 atm vapor pressure = 1 atm BOILING Slide 38: 38 PHASE DIAGRAMS: (Temperature vs. Pressure) (all 3 phases exists here) gas and liquid are indistinguishable. critical temperature and critical pressure Slide 39: 39 H2O CO2 note slope with pressure note slope with pressure Slide 40: 40 Crystal Structures: Slide 41: 41 unit cells: contains 1 atom contains 2 atoms Slide 42: 42 Slide 43: 43 Slide 44: 44 Slide 45: 45

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