Chemistry Bonding Images

HF Electron Bonding Density

These images are provided by Mike Ellison, Lori Lancaster, and Rosa Hemphill for high school teachers and students studying chemical bonding. They were produced in the lab of Dr. Gwen Shusterman at Portland State University using Spartan on an SGI computer.


"For the images below, variation in electrostatic potential or electron density are shown using different colors. Positive electrostatic potential is shown as shades of blue and negative electrostatic potential as reds. High electron density is also shown as shades of blue, and low (approx. zero) electron density as reds" (PC Alan Shusterman).

How do you "see" the electrons in HF, which has a predominantly covalent bond? We usually think of covalent bonds as those in which electrons are shared between two atoms. Click here to see a Spartan-produced mapping of the HF bond.

How do you "see" the electrons that form the bond in NaCl? Click here to see a Spartan-produced mapping of the electron density of the NaCl bond. [This image is an isosurface drawn at a specific electron density (0.002); the color on it is the electrostatic potential. Once can visualize both electron density and electrostatic potential.]

Another parameter we can use to "see" the role electrons play in bonding is the idea of electrostatic potential. For this, imagine a positive charge (+). Now imagine moving that positive charge around a bonding set of atoms, eg, NaCl. You use color to show where the charge feels an attraction and repulsion. The shade of color is used to represent the strength of the electrostatic force. What would the map of this electrostatic potential (elpot) look like. Click here to see a Spartan-produced mapping of the electrostatic potential of the NaCl bond. [This image is an isosurface drawn at a specific electron density (0.002).]


As one goes across the periodic table, visualization programs such as Spartan make it possible to see the effect of bonding to progressively more electronegative atoms...
Click on the following molecules to see the electron density models from selected period 2 atoms combining with hydrogen... These are isosurfaces drawn at a specific electron density (0.002). The color is the electrostatic potential. This then has both electron density and electrostatic potential being visualized. (These images may each take a short while to load)

BeH2.
 
 

CH4
 
 
 

NH3
 
 
 

H2O
 
 
 

HF
 


To see the similarily between two non-polar molecules, H2 and Cl2, click on the links below...

H-H bonding
 
 
 

A slice through the electron density volume of Cl-Cl single bond
 
 


To see the effect of bonding across Period 3 (as chlorine bonds to each element in Period 3), click on the compounds below. The images will be electron density slices through the molecule (or formula unit)...

NaCl bonding...Note that there is little sharing of electrons between the two ions.
 
 
 
 
 

MgCl2
 
 
 
 

AlCl3...Again, note the increasing amount of green between the atoms.
 

SiCl4
 

PCl3
 

PCl3, rotated.
 
 
 

PCl5
 
 
 

PCl5, slices...This image shows the electron density via a set of slices so you can better see the five chlorines.
 

SCl2
 

Cl-Cl bonding...Note the electron density between the two chlorines and the balanced distribution of electron density in the slice.
 


As you go DOWN a column of the periodic table, such as the halogen, you can again expect to see differences in the "sharing" of electrons as the electronegative "pulling" of the halogen changes....
 

Slices of electron density for the HX series..Click here to see the electron distribution from slices through the electron density volumes of HF, HCl, HBr, and HI [Note, the range of electron densities may vary among the molecules].
 
 
 
 
 
 


Finally, to get a comparison of the effect of substituting an electronegative atom in a non-polar molecule, click on the next image. Although the images are light, you can see the effect of progressive substitution of chlorine into the methane molecule. Both the shape and the electron density of the molecules change with increasing Cl substitution, until with CCl4, you once again have a non-polar, balanced molecule. You can see that the individual bonds are more polar than they were in CH4.
Electron Density as Methane becomes substituted with Cl
 


For comments or suggestions, please email me at hemphill@spiretech.com
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