Welcome to the CAChe Molecular Modeling Tutorials

Department of Chemistry

University of Pittsburgh at Johnstown

Home
Getting Started
The Basics of CAChe
The User Interface
Simple Molecules
Inorganic Molecules & Ions
Organic Molecules
The Fragment Library
Viewing & Manipulating
Computing Properties
Optimizing Geometry
Molecular Orbitals
Spectral Properties
Predicting Reactivity
Energy Maps
General Chemistry
Ferrocene

Modifying a Structure III

Task: Modify Ozone, O3 , to build sulfur dioxide, SO2

Time: 7 minutes

The structures of ozone and sulfur dioxide are very similar.  Suppose we want to build a molecule of SO2. We could start from scratch ... or we could use the existing ozone molecule, make a few modifications and voila, we have it! As with our ozone structure, it will help to draw the Lewis structure and determine the Formal Charge on the sulfur and each of the oxygen atoms. 

  1. Open the "ozone" file you created previously and change the name by selecting File|Save As . Name the new file "SO2".
  2. Click on the select tool, , select the central oxygen atom.  Then select the arrow button in the element type box and select sulfur.  If sulfur is not in the Atom List, choose Periodic Table... , select sulfur from the Periodic Table and click OK.
  3. When you select sulfur from the element type box, the red oxygen atom becomes a yellow sulfur atom.
  4. Compare your structure to the Lewis structure you drew.  Adjust the bond order if necessary.  Follow the same steps as you did for ozone.
  5. The hybridization on the sulfur, should be the same as the central oxygen in the ozone molecule.  If not, click on the select tool , to select the sulfur atom, select the arrow button in the hybridization type box and select sp2 -trigonal plane . Use this same approach to check the hybridization on the two oxygen atoms.
  6. We also need to check the Formal Charges.  Compare the Lewis structure you drew at the beginning of this exercise with your CAChe structure.  If you need to change the charges, click on the select tool , select the atom, then click the up or down arrow button in the charge box to select appropriate charge for that atom. Repeat this step for each of the each atom as needed.
  7. Click on the select tool and click in the workspace (not on any atoms or bonds) to select the entire molecule.
  8. To fix the geometry of the ozone molecule, select Beautify|Geometry from the menu bar. 
  9. To save your finished molecule select File|Save and save it as "SO2".

In the next lesson you will build a nitrate ion.