IMF 2016.notebook
March 18, 2016
What is an Intermolecular force?
Intramolecular bond:
Intermolecular Forces of Attraction (IMF)
Aim: What are the forces behind the attractions
between molecules?
Intermolecular force (IMF):
All IMF are attractions between opposite partially
charged ends of molecules.
The IMF determines the type of mp, bp, vapor pressure
and surface tension a molecular substance will have.
Dec 10­9:57 AM
Dec 10­10:05 AM
Inter vs. Intra
Intrastate (red)
Attractions in Space
Interstate (blue)
Mar 17­9:31 AM
Dec 11­6:56 PM
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IMF 2016.notebook
March 18, 2016
Types of Intermolecular Forces
STRONGEST
• Hydrogen "Bonding"
• Dipole­Dipole Forces
• Van der Waals Forces (Weak Forces)
WEAKEST
H2O
mp= 0°C
bp= 100°C
Dec 10­10:51 AM
Hydrogen Bonds
Acetone
mp= ­95°C
bp= 56 °C
Dec 11­7:23 PM
Dipole­Dipole Forces
• Strongest IMF between molecules.
• Attraction is between the opposite partial charges of the
molecules in H2O, HF and NH3 only. (For molecules of the same
substance)
(Hydrogen bonding is FON!)
• Second strongest IMF.
• Occurs between the ends of polar molecules with
opposite partial charges.
• Causes substances to have very high MP, BP, vapor
pressures and surface tension for molecular substances.
Dec 10­10:14 AM
Dec 10­10:11 AM
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IMF 2016.notebook
March 18, 2016
Van Der Waals Forces (VDF/Weak Force)
Molecule­Ion Attractions ex: NaCl (aq)
• Weakest intermolecular force.
• Occurs between nonpolar molecules
with symmetry when temporary "dipoles"
form.
• Halogens and noble gases have VDF.
• The larger the molecule, the stronger the
VDF attractions.
Dec 10­5:20 PM
Dec 10­5:20 PM
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