Molecular Polarity Guided Inquiry v3
Essential Questions
 How do the bonds between atoms, as well as electron location, determine interactions between molecules?
 How do electronegativity and molecular shape determine the polarity of a molecule?
How does Bond Polarity affect Molecular Polarity?
Molecule Polarity – is a measure of how electrons are distributed in the outer regions of the molecule. It is
similar to bond polarity in that it is a measure of how unequally electrons are shared. It is different than
bond polarity because bond polarity is a measure of how unequally the electrons are shared in a bond,
while molecular polarity is a measure of how unequally the electrons are distributed throughout the outer
region of the entire molecule, not just a particular bond. Molecular polarity is the sum of all the bond
polarities. A highly polar molecule will have an uneven distribution of electrons around the outer regions of
the molecule, which will result in areas of positive and negative charges.
The image on the left shows water, H2O, with two highly polar O-H bonds. The negative ends of dipoles are
pointing toward the oxygen. This coupled with the asymmetrical (bent) shape of the water molecule causes
an uneven distribution of electrons throughout
the outer regions of the molecule. The image on
the right shows the electron density for water.
Notice that the density is much higher on the
oxygen side of the molecule than at either of the
hydrogen sides. This results in a partial negative
charge at the oxygen side and partial negative
charges at the hydrogen sides.
How does Molecular Shape affect Molecular Polarity?
A non-polar molecule has the electrons uniformly distributed around the outer edges. A non-polar
molecule can have polar bonds if the bonds are arranged symmetrically so the electrons are distributed
uniformly throughout the outer regions of the molecule. Carbon tetrafluoride, CF4, is an example of a nonpolar molecule with 4 highly polar bonds. The image on the left shows CF4 with four highly polar C-F bonds.
The image on the right shows the electron
density of the CF4 molecule. The electron
density is uniform throughout the outer regions
of the molecule. That’s because the 4 strong C-F
bond dipoles are arranged symmetrically in
opposite directions. So they cancel each other
out. The net result is that there are no areas of
positive and negative partial charges in the outer
region of the molecule.
Molecule Polarity Simulation w/ 3 Atoms
Run the Molecule Polarity simulation from the PhET web site:
http://phet.colorado.edu/en/simulation/molecule-polarity.
Select the “Three Atom” tab at the top of the screen. Set the View box to show
the bond dipole, molecular dipole and partial charges. Turn the electric field
off. Run the simulation with different combinations of electronegativities for
atoms A, B and C as specified in the data table below. Run each combination of
electronegativies for the bent molecular shape and the linear molecular shape.
Watch what happens to the size and direction of the bond dipoles, molecular
dipoles and partial charges. Record your observations in the data table. Use
your results to answer the questions. Use the key below to help you run the simulation.
 Electronegativity Settings: less, middle and more
 Bond Dipole & Molecular Dipole Strength: zero, low, medium and strong
 Direction: north, south, east, west, northeast, northwest, southeast and southwest
Electronegativity
Settings
A – B Bond Dipole
Atom
A
Atom
B
Atom
C
Less
Less
Less
Less
Less
Mid
Less
Less
More
Less
Mid
Less
Less
Mid
Mid
Less
Mid
More
Mid
Less
Less
Mid
Less
Mid
Mid
Less
More
Mid
Mid
Less
Mid
Mid
Mid
Mid
Mid
More
Mid
More
Less
Mid
More
Mid
Mid
More
More
More
Mid
Less
More
Mid
Mid
More
Mid
More
Strength
Direction
C – B Bond Dipole
Strength
Direction
Bent Molecule
Molecular Dipole
Strength
Direction
Linear Molecule
Molecular Dipole
Strength
Direction
1. Explain how a bent (aka asymmetrical) molecule can be non-polar.
2. Explain how a linear (aka symmetrical) molecule can be non-polar.
3. Explain how the bent (aka asymmetrical) molecule can be polar.
4. Explain how the linear (aka symmetrical) molecule can be polar.
5. Explain how individual bond dipoles and molecular shape contribute to the overall molecular dipole?
Molecule Polarity Simulation w/ Real Molecules (http://phet.colorado.edu/en/simulation/molecule-polarity)
In the previous simulation with 3 atoms we were able to see how the individual bond dipoles and the molecular
shape, linear or bent, affected the overall molecular dipole. In this simulation, we will learn how other
symmetrical and asymmetrical shapes affect the overall molecular dipole.
Select the “Real Molecules” tab at the top of the screen. Pick linear, bent, trigonal planar, trigonal pyramidal and
tetrahedral molecules from the list. Build the 3D model of the molecule, label the positive and negative poles of
the 3D model, and complete the information below.
Molecular
Formula
Lewis Dot structure
Molecular
Shape
Linear
Bent
Trigonal
planar
Trigonal
pyramidal
tetrahedral
Sketch the Molecule with Bond
Dipoles and Molecular Dipoles