Explore molecule polarity.
Whether a molecule is polar depends on both the polarity of its individual bonds and the shape of the molecule.
This interactive PhET simulation allows you to explore how differences in electronegativity produce bond dipoles and how the three-dimensional arrangement
of those dipoles determines whether a molecule has an overall molecular dipole.
Experiment with the model rather than simply observing it.
Change the electronegativities of the atoms, alter the molecular geometry and predict the effect on bond polarity and overall molecular polarity before revealing the result.
Molecule Polarity is provided by PhET Interactive Simulations, University of Colorado Boulder, and is used under the CC BY-NC 4.0 licence.
1. Create a bond dipole
Start with the Two Atoms model. Make the two atoms have the same electronegativity. What happens to the electron distribution and bond dipole? Now increase the electronegativity of one atom. Predict which end of the bond becomes δ+ and which becomes δ−.
2. Investigate electronegativity difference
Gradually increase the difference in electronegativity between the two atoms. What happens to the size of the bond dipole? What relationship can you identify between electronegativity difference and bond polarity?
3. Reverse the bond dipole
Without moving the atoms, change their electronegativities so that the direction of the bond dipole reverses. Explain why the dipole arrow changes direction.
4. Move from bonds to molecules
Switch to the Three Atoms model. Create two polar bonds. Does having polar bonds necessarily mean that the whole molecule is polar? Experiment with the arrangement of the atoms and observe the overall molecular dipole.
5. Make the dipoles cancel
Try to produce a molecule containing polar bonds but with no overall molecular dipole. What must be true about the individual bond dipoles and their arrangement?
6. Make the molecule polar
Now change the arrangement so that the individual bond dipoles no longer cancel. Explain why the molecule now has a resultant molecular dipole.
7. Explore real molecules
Move to Real Molecules. Before displaying the molecular dipole, examine the bonds and molecular shape and predict whether each molecule will be polar or non-polar. Then use the simulation to check your prediction.
As you explore, keep asking:
Are the bonds polar — and, if they are, do their bond dipoles cancel because of the shape of the molecule?
That distinction between bond polarity and molecular polarity is the central idea.