Polar and Nonpolar Molecules
by Ed Tuthill

This website will help you to understand the difference between POLAR and NONPOLAR molecules by helping you visualize how the electrons are distributed in POLAR molecules compared to NONPOLAR molecules.

In order to view this page you will need
to download the free plug-in Chemscape Chime.

chime logo

Boron trihydride
Carbon tetrabromide
Carbon dioxide
Most of this navigation bar is internationally not active at this time. When you get to the fourth page, Ammonia, it will become fully active.

Nonpolar Molecules

In some molecules, the bonding electrons are evenly distributed so that both ends of the molecule have the same amount of negative or positive charge.  Therefore, there is no difference between the two ends, neither one is more negative or positive than the other.  Such a molecule is considered to be NONPOLAR since there is not a positive and a negative side. This situation can result from: 1) the bonds not being very polar, 2) the molecule being symmetrical, or 3) both.

Sulfur Trioxide is a good example of a symmetrical molecule which is nonpolar.

As before, place the mouse cursor over the image. Click the right mouse button to bring up the chime menu and click on rotation. To stop the rotation, bring up the chime menu again and click on rotation. Do you see that if you connected the three oxygen atoms, the red ones that stick out, that the molecule has the shape of an equilateral triangle and is therefore symmetrical. If you hold the shift key while you hold down the left mouse button, and move the cursor up or down, you can increase or decrease the size of the molecule. Orient the molecule to make an equilateral triangle and so that you can see all 4 atoms and make the molecule as big as possible.

Now follow the directions below the molecule.

In order to visualize the distribution of the outer electrons and the resulting electrostatic charge for this molecule, do the following:

  1. With your cursor on the model, click the right mouse button to open the Chime menu. (On a Mac, Click the mouse on the molecule and hold the click.) 
  2. Go to Select, then to Display List, and finally to Create Molecular Surface. This changes the look of the molecule to show the outer surface of the space occupied by the electrons.
  3. Right click on the molecule again and choose Select, Display List, Color, Electrostatic Potential and finally Color Red-White-Blue.  This shows the overall distribution of charge on the surface of the molecule.  In this color scheme, the dark blue represents the most positive and the dark red represents the most negative.

Now rotate the molecule to view it from all sides.

Notice that all the dark red (negative) is on the outside of the molecule and all of the dark blue (positive) is on the inside.  This causes the molecule to be NONPOLAR because all the outermost parts of the molecule have the same electrostatic charge. Therefore, no side is noticeably more negative than the other.

Now look at another very important example of nonpolar molecules. NEXT EXAMPLE