2. Polar vs. Non-Polar Molecules
Polar vs. Non-Polar Molecules
Polarity in a molecules determines
Polarity in a molecules determines
whether or not electrons in that
whether or not electrons in that
molecule are shared equally.
molecule are shared equally.
When determining the polarity of a
When determining the polarity of a
molecule, it is all about
molecule, it is all about symmetry.
symmetry.
Asymmetric molecules tend to be polar.
Asymmetric molecules tend to be polar.
Symmetric molecules are always non-
Symmetric molecules are always non-
polar.
polar.
3. When determining the polarity of a
When determining the polarity of a
molecule, follow these steps:
molecule, follow these steps:
Draw the Electron Dot structure of the
Draw the Electron Dot structure of the
molecule.
molecule.
Using the electronegativity chart determine
Using the electronegativity chart determine
the difference in electronegativity for each
the difference in electronegativity for each
bond.
bond.
0—0.4 = Non-polar
0—0.4 = Non-polar
0.5—1.7 = Polar
0.5—1.7 = Polar
4. The molecule is
The molecule is non-polar
non-polar if :
if :
each bond in the molecule is non-polar
each bond in the molecule is non-polar
and there are
and there are no
no
unbonded electron pairs.
unbonded electron pairs.
each bond in the molecule has the same
each bond in the molecule has the same
polarity and there
polarity and there
are
are no
no unbonded electron pairs on
unbonded electron pairs on
the central atom.
the central atom.
There is no net dipole moment (all
There is no net dipole moment (all
moments cancel out)
moments cancel out)
5. The molecule is
The molecule is polar
polar if:
if:
There is a net dipole moment
There is a net dipole moment
each bond in the molecule is non-polar,
each bond in the molecule is non-polar,
but there
but there are
are unbonded electron pairs on
unbonded electron pairs on
the central atom.
the central atom.
bonds in the molecule have different
bonds in the molecule have different
polarities and/or there
polarities and/or there
are
are unbonded electron pairs on the
unbonded electron pairs on the
central atom.
central atom.
6. Dipole Moments
Dipole Moments
Dipole Moments
Dipole Moments (μ) - a quantitative
(μ) - a quantitative
measure of the polarity of a bond.
measure of the polarity of a bond.
μ = charge x distance = Q x r
μ = charge x distance = Q x r
(distance is in meters)
(distance is in meters)
Dipole moment units are the Debye
Dipole moment units are the Debye
Bond dipole moment is a vector quantity –
Bond dipole moment is a vector quantity –
it has a magnitude and direction.
it has a magnitude and direction.
Molecular dipole moment = vector sum of
Molecular dipole moment = vector sum of
all bond moments
all bond moments
7. Dipole Moment
Dipole Moment
Direction of the polar bond in a molecule.
Direction of the polar bond in a molecule.
Arrow points toward the more e
Arrow points toward the more e-
-
neg atom.
neg atom.
H Cl
+
-
9. Polar Molecules
Polar Molecules
– Dipole moments are asymmetrical and
Dipole moments are asymmetrical and
don’t cancel .
don’t cancel .
– Molecule has a net dipole moment.
Molecule has a net dipole moment.
net
dipole
moment
H2O
H H
O
11. Polar Bonds vs. Polar Molecules
Polar Bonds vs. Polar Molecules
The effect of polar bonds on the
The effect of polar bonds on the
polarity of the entire molecule
polarity of the entire molecule
depends on the
depends on the molecule shape
molecule shape
– carbon dioxide has two polar bonds, and
carbon dioxide has two polar bonds, and
is linear =
is linear = nonpolar molecule
nonpolar molecule!
!
12. Polar molecules
Polar molecules
The effect of polar bonds on the
The effect of polar bonds on the
polarity of the entire molecule depends
polarity of the entire molecule depends
on the
on the molecule shape
molecule shape
– water has two polar bonds and a bent shape;
water has two polar bonds and a bent shape;
the highly electronegative oxygen pulls the e
the highly electronegative oxygen pulls the e-
-
away from H = very polar!
away from H = very polar!
13. CHCl3
H
Cl Cl
Cl
Determining Molecular Polarity
Determining Molecular Polarity
Therefore, polar molecules have...
Therefore, polar molecules have...
– asymmetrical shape (lone pairs) or
asymmetrical shape (lone pairs) or
– asymmetrical atoms
asymmetrical atoms
net
dipole
moment
