Woodrow Wilson Department of
SCIENCE
Chemistry Fall 2013
Messenger
Do Now:
Grab your chromatography plates, and
sit with your lab group.
Measure the Rf of the spots, if you have
not already.
Woodrow Wilson Department of
SCIENCE
Chemistry Fall 2013
Messenger
Today’s Agenda
Intermolecular Forces Part 2
Finish Lab & Work on Post Lab
Post-lab due TOMORROW!
(Not the abstract)
Woodrow Wilson Department of
SCIENCE
Chemistry Fall 2013
Messenger
Intramolecular Forces: the forces
between atoms within one molecule
Intermolecular Forces: the forces
between molecules of a substance.
Woodrow Wilson Department of
Chemistry Fall 2013
Messenger
SCIENCE
London Dispersion Forces (LDF’s)
moving
polar.
Woodrow Wilson Department of
SCIENCE
Chemistry Fall 2013
Messenger
• Remember electrons are always
moving in a cloud.
• We can only ever know the
PROBABILITY of where the electrons
are.
Woodrow Wilson Department of
SCIENCE
Chemistry Fall 2013
Messenger
Because of this, there is a probability
that the electrons all end up lopsided
unequally for a split second.
This induces a VERY temporary dipole.
Woodrow Wilson Department of
SCIENCE
Chemistry Fall 2013
Messenger
This temporary polar molecule can pull
the electrons from other molecules and
induce similar, short lived dipoles.
This is part of the London Dispersion
Force. It is the weakest intermolecular
force.
Woodrow Wilson Department of
Chemistry Fall 2013
Messenger
SCIENCE
electronegativity
partial charge
Woodrow Wilson Department of
SCIENCE
Chemistry Fall 2013
Messenger
Woodrow Wilson Department of
Chemistry Fall 2013
Messenger
SCIENCE
Hydrogen Bonding
Proton (+)
O
Hydrogen bonds
Ionic bonds
F
N
Woodrow Wilson Department of
SCIENCE
Chemistry Fall 2013
Messenger
We can represent hydrogen bonds as a
dotted line between hydrogen and our
electronegative atom.
Whiteboards: Draw the hydrogen
bonding of H2O.
Woodrow Wilson Department of
SCIENCE
Chemistry Fall 2013
Messenger
Woodrow Wilson Department of
Chemistry Fall 2013
Messenger
SCIENCE
Dipole-Ion Forces
polar
Woodrow Wilson Department of
SCIENCE
Chemistry Fall 2013
Messenger
Woodrow Wilson Department of
SCIENCE
Ion-Ion Forces
Coulomb’s Law
decreases
bigger
Chemistry Fall 2013
Messenger
Woodrow Wilson Department of
Chemistry Fall 2013
Messenger
SCIENCE
Vapor Pressure and IMFs
The pressure exerted by a gas above a liquid. (The more gas molecules above a
liquid the higher the vapor pressure).
fewer
lower
Strong intermolecular forces means low vapor pressure
Woodrow Wilson Department of
SCIENCE
Chemistry Fall 2013
Messenger