Looking at Molecular Polarity

First let's examine a variety of representations of the same molecule, hydrogen chloride (HCl).  Place the cursor on each molecule, click, and rotate.  Which element is more electronegative?  What direction do the electrons migrate in the bond?

ball and stick            space-filled            electrostatic potential

On the electrostatic potential map, which illustrates the distribution of charge on a molecule, red is negative and blue is positive (see figure below for the red-white-blue color scheme).

Now let's examine methane, CH₄.  This electrostatic potential map uses the Rasmol color scheme given below:

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

space filled        electrostatic potential

How would you characterize the charge surface on methane?

Since the carbon in methane is slightly more electronegative than the hydrogen, the hydrogen has a slight positive charge associated with it.  The charge distribution is symmetrical about the molecule.

Let's explore the series of chloromethanes given in the images below.  From the molecular structures below, rank the order of polarity for the four molecules.

 CH₃Cl                      CH₂Cl₂                    CHCl₃                        CCl₄

The buttons above will convert the molecules to the electrostatic potential maps.  Does using the electrostatic potential maps change your ranking?

The molecular structures of NCl₃, where DEN = 0 for N-Cl bond, and NH₃, where DEN = 0.9 for the N-H bond, are given below.   For NCl₃, is the molecule polar?  Explain. 

Does the charge distribution on NH₃ seem reasonable?  Click on the buttons above. Explain.

Now examine the structures of H₂O, H₂S, OF₂, and SF₂.  Explain the polarity of these molecules.

What is unusual about SF₂?

Here are two trigonal planar molecules, CH₂O and SO₃.  Explain there different behavior.

Return to Gage CHM 101 webpage or Sinex CHM 101 webpage.

Barbara Gage        Scott Sinex        Prince George's Community College        10/2002