Creating an Electrostatic Potential on the Molecular Surface  

This is a two step process to get the electrostatic potential or the degree of partial charge located on a molecule using Chime.  First you need to create the molecular surface or what the molecule looks like as shown on the menu below.

The second step is to select the color scheme to represent the variation in charge from positive to negative.

Here are the symmetrical charge distribution for CO2 (left) and asymmetrical one for H2O (right) using the Color Red-White-Blue.  Where are the more negative areas of the molecules?  Why?

            

For CO2, the electronegative oxygens (red) pull electrons away from the central carbon atom (blue).  For H2O, the two lone pairs of electrons on the oxygen cause the negative area. 

Electrostatic Potential for the Halomethanes:  Use the menu instructions above to convert these molecular images into their electrostatic potential with the Rasmol color scheme.

CH4   CH3Cl CH2Cl2  CHCl3 CCl4

Source: http://www.cmbi.kun.nl/wetche/organic/

How can you tell a polar molecule from a non-polar molecule?

Can you describe a difference in polarity for the polar molecules?

Non-polar molecules have a symmetrical charge distribution, while a polar molecule has an asymmetrical charge distribution.  From dipole moment measurements, CH3Cl  is the most polar.

What about the 1-nitro-4-chlorobenzene molecule below - polar or nonpolar?  The electrostatic potential is shown on the right with the same orientation as the molecular structure to the left.

See Looking at Molecular Polarity for further use of electrostatic potential maps.

Many of the molecules have been produced on the Mol4D editor.  This is a great site!

Back to the Student Guide

Scott A. Sinex    Prince George's Community College        8/2005