Intermolecular Forces: - PowerPoint PPT Presentation

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Intermolecular Forces:

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Title: Liquids, Solids, and Phase Changes Author: Paul Charlesworth Last modified by: Charles Marth Created Date: 3/4/2003 2:33:42 AM Document presentation format – PowerPoint PPT presentation

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Title: Intermolecular Forces:


1
Intermolecular Forces
  • - Attractive forces between molecules and ions,
    based on polarity
  • - Determine bulk properties of matter example
    solid vs. liquid vs. gas
  • - Much weaker than intramolecular forces such as
    covalent bonds and ionic bonds

2
Intermolecular Forces 01
  • Type of Intermolecular Forces
  • Dipoledipole
  • Hydrogen Bonds
  • London Force (instantaneous induced dipole)

3
Intermolecular Forces 03
  • IonDipole Between polar molecules and
    ions. opposites attract

4
Intermolecular Forces 02
  • DipoleDipole Between polar molecules.
    Polar molecules

5
Intermolecular Forces 05
  • Hydrogen Bond Molecules containing NH, OH, or
    FH groups, and an electronegative O, N, or F.
  • This type of dipole-dipole force is especially
    strong, since the partial positive charge on H is
    high.
  • The H on the electronegative element is d, and
    is strongly attracted to the lone pair of
    electrons in a different molecule.

H-bonding is a special type of dipole-dipole
force that is especially strong. It is an
intermolecular force,
6
Intermolecular Forces 05
  • Hydrogen Bond Molecules containing NH, OH, or
    FH groups, and an electronegative O, N, or F.

Strength of hydrogen bonds can be observed by
looking at boiling points of various compounds.
7
Intermolecular Forces 05
  • Boiling points for different compounds of Group
    4A, 5A, and 6A.

8
Intermolecular Forces 04
  • The element bromine is a liquid, composed of Br2
    molecules.

A moleculeof Br2
Bromine is a liquid, but non-polar. What holds
bromine molecules together as a liquid?
9
Intermolecular Forces 04
  • London Dispersion Forces Attraction is due to
    instantaneous, temporary dipoles formed due to
    electron motion.

10
Review
What intermolecular forces will operate between
molecules in the substances below?
Cl2 CH3OCH3 Cl-NH2 Ar
CH3CH2CH3
11
Intermolecular Forces 06
very
veryweak
12
Intermolecular Forces 07
Effect on Boiling Point
  • CH4 110 K
  • SiH4 160 K
  • GeH4 175 K
  • SnH4 215 K
  • H2O 373 K
  • H2S 215 K
  • H2Se 225 K
  • H2Te 270 K

Force
13
Intermolecular Forces 08
  • Surface Tension is the resistance of a liquid to
    spread out and increase its surface area.
  • Surface tension results from intermolecular force
    differences between molecules in the interior of
    a liquid and those on the surface.

14
Intermolecular Forces 09
  • Viscosity is the measure of a liquids
    resistance to flow. It is related to the ease
    with which molecules move around and thus to
    intermolecular forces.

Low Viscosity
High Viscosity
15
Phase Changes 01
16
Phase Changes 02
  • Molar Heat of Fusion (?Hfus) The energy
    required to melt one mole of solid (in kJ).
  • Molar Heat of Vaporization (?Hvap) The energy
    (in kJ) required to vaporize one mole of liquid.

17
Phase Changes 02
18
Phase Changes 04
  • Sublimation The process in which molecules go
    directly from the solid into the vapor phase.
  • Deposition The process in which molecules go
    directly from the vapor into the solid phase.
  • Molar heat of sublimation (?Hsub) The energy
    (kJ) required to sublime one mole of solid.

19
Phase Changes 06
  • Vapor Pressure The pressure exerted by gaseous
    molecules above a liquid.
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