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.

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Polar (Home)

Polar Molecules

All molecules are electrically neutral if you consider the whole molecule and the number of protons and electrons. However, if we"look" at finer detail we find that in some molecules the distribution of electrons is lopsided. That is, the electrons tend to "concentrate" on one side more than the other. This causes one side of the molecule to be more negative than the other. Such a molecule is POLAR. It has a negative pole (the side where the electrons are more concentrated) and a positive pole (the side where the electrons are less concentrated). There are two main factors that determine if a molecule is polar or nonpolar: 1) the degree of polarity in the bonds 2) the symmetry of the molecule. In order for a molecule to be polar the bonds must be definitely polar and the molecule needs to be asymmetrical.

Water is one of the best molecules to illustrate polarity. The model of a water molecule below can be manipulated to clearly show why it is polar.

First place the mouse cursor over the image. Click and hold the left mouse button and move the mouse around. This will rotate the model. You can clearly see that the molecule has an angular shape and is therefore asymmetrical. The bonds in a water molecule are very polar because the oxygen atoms attract the bonding electrons quite a bit more strongly than the hydrogen atoms do. To see how these factors combine to make a polar molecule, follow the directions below the molecule.

If you hold the shift key while you left click, hold, and move the cursor up or down, you can increase or decrease the size of the molecule. Orient the molecule so that you can see all three atoms and make the molecule as big as possible.

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 one side of the molecule and all of the dark blue (positive) is on the other side.  This causes the molecule to be POLAR, that is to have one end that is noticeably more negative than the other.
The next page will teach you about NONPOLAR molecules.

Check out the following websites for further explanations about:

Polar bonds:
http://www.chem.vt.edu/RVGS/ACT/notes/electronegativity.htm

Polar and nonploar molecules
1. Ask a Scientist
2. Polar Molecules by Mark Bishop

The molecular models are part of the OUC molecular models database. Copyright 1996,1997,1998,1999, 2000, 2001
Models may be used for educational or personal purposes, but may not be copied for publishing use without permission of the author Dave Woodcock.