INTERMOLECULAR FORCESChap. 13: Day 2
Type of Bond determines ForcesGenerally strongestInterparticleIonic BondIon-ion force
Metalic bondElectronic force
Generally weakerintermolecular forcesCovalent bondsPolar moleculesDipole forcesNonpolar moleculesLondon DispersonInduced dipole forces
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)
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)
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.
NONPOLAR MoleculesWhat causes the differences in intermolecular forces between molecules?Why do the intermolecular forces vary between nonpolar molecules?
LiquidSolidWHY?
Bigger Molecules interact more
DISPERSION FORCENonpolar Molecules
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.
DIPOLE FORCEPolar Molecules
More polar stronger force
Why different?liquidgas
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SOME POLAR MoleculesHave specialDipole force with HydrogenHYDROGEN FORCE orHYDROGEN BOND
HYDOGEN BOND NEED TO BE POLARH is attached to N, F, or O
ALL molecules have LONDON DISPERSION force
Graphing: Intermolecular ForcesSee handout4 different FamiliesBoiling point vs periodBoiling pointperiod100 k400 k26