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