INTERMOLECULAR FORCES
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Transcript of INTERMOLECULAR FORCES
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INTERMOLECULAR FORCESChap. 13: Day 2
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Type of Bond determines ForcesGenerally strongestInterparticleIonic BondIon-ion force
Metalic bondElectronic force
Generally weakerintermolecular forcesCovalent bondsPolar moleculesDipole forcesNonpolar moleculesLondon DispersonInduced dipole forces
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Melting PointEnergy needed over come the intermolecular forces between molecules in the solid phaseTemperature at which molecules in a solid gain enough potential energy to change position (become L)
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Boiling PointEnergy needed over come the intermolecular forces between molecules in the liquid phaseTemperature at which molecules in a liquid gain enough potential energy to change position (become gas)
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POLAR vs NONPOLAR
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Molecular PolarityMolecules will be polar ifa)bonds are polar ANDthe molecule is NOT symmetric
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Polar or Nonpolar?Compare CO2 and H2O. Which one is polar?
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Polar or Nonpolar?Consider AB3 molecules: BF3, Cl2CO, and NH3.
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Molecular Polarity, BF3 B atom is positive and F atoms are negative.BF bonds in BF3 are polar. But molecule is symmetrical and NOT polar
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Molecular Polarity, HBF2B atom is positive but H & F atoms are negative.BF and BH bonds in HBF2 are polar. But molecule is NOT symmetrical and is polar.
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Is Methane, CH4, Polar?Methane is symmetrical and is NOT polar.
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Substituted EthyleneCF bonds are MUCH more polar than CH bonds. Because both CF bonds are on same side of molecule, molecule is POLAR.
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NONPOLAR MoleculesWhat causes the differences in intermolecular forces between molecules?Why do the intermolecular forces vary between nonpolar molecules?
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LiquidSolidWHY?
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Bigger Molecules interact more
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DISPERSION FORCENonpolar Molecules
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POLAR MoleculesWhy do the intermolecular forces vary between polar molecules?
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Molecular PolarityMoleculessuch as HCl and H2O can be POLAR (or dipolar). They have a DIPOLE MOMENT. The polar HCl molecule will turn to align with an electric field.
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DIPOLE FORCEPolar Molecules
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More polar stronger force
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Why different?liquidgas
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SOME POLAR MoleculesHave specialDipole force with HydrogenHYDROGEN FORCE orHYDROGEN BOND
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HYDOGEN BOND NEED TO BE POLARH is attached to N, F, or O
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ALL molecules have LONDON DISPERSION force
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Graphing: Intermolecular ForcesSee handout4 different FamiliesBoiling point vs periodBoiling pointperiod100 k400 k26