Molecular Polarity

The polarity of a molecule is an important physical property. Polarity can help predict whether a molecule is soluble in another substance. As we’ll see in Module J, it can also explain why seemingly similar compounds have very different melting and boiling points. For drug manufacturers, the polarity of a drug is important if it needs to diffuse across a phospholipid bilayer. Too polar, and the drug stays dissolved in the aqueous regions (e.g., blood) and never makes it into the interior of the cell. Too non-polar and the drug gets stuck in the interior of the phospholipid bilayer which is also non-polar.

In order to determine whether a molecule is polar, you need to know two pieces of information: does the compound have polar bonds and what is the molecular shape? Polar covalent bonds are dependent on the electronegativity difference between atoms and shape is predicted using VSEPR. For a review of these concepts, read Chapter 10 in your textbook.

Investigation
You will use the PhET simulation to investigate the relationship between shape, electronegativity and polarity. Go to the following URL: https://phet.colorado.edu/sims/html/molecule-polarity/latest/molecule-polarity_en.html.

A. Start by clicking on the Two Atoms simulation.

Turn on the electric field.
Change the electronegativity of both atoms and observe the movement of the molecule.
Which end of the molecule is nearest the negative plate and which is nearest the positive plate?
Drag the atoms into different positions. What effect does that have on polarity? How do you know?
How can the molecule be made the most polar and the least polar?
B. Repeat the investigation above with the Three Atoms example. Pay close attention to shape as you drag the atoms into different positions.