These days a good bit of chemistry can be modeled on a computer. From extremely accurate predictions of small molecule properties to drug design, computational chemistry has grown into a HUGE field. HYPERCHEM is a commercial computational chemistry package that can do many interesting things. What you will be doing today is just a tiny part. So let’s get started. The best way to figure it out is by example.

1. Double-click on the "ChemLite" Icon (green test tube). The HYPERCHEM working window comes up. You should be seeing a black screen with a bunch of icons and pull-down menus at the top. Let’s build a molecule.
2. Double-click on the "Draw" icon  . A periodic table appears. Make sure that the "Allow Ions" box is checked and the "Explicit Hydrogens" box is not checked. You can move the periodic table out of the way in order to work on the screen.
3. Select the atom you want. As an example Let’s make the molecule CH2NH. The Lewis structure for this molecule is: 
4. Select N from the Periodic table and left-click anywhere on the screen. You will see a dark blue circle (the atoms are color coded, C=light blue, N=dark blue, O=red, F=yellow, H=white). If you wish to remove an atom, move the "Draw" icon over that atom and right-click.
5. Select hydrogen from the periodic table. Left-click and hold while you drag the cursor above the nitrogen. When you release the mouse button you will see an H (white) bonded to an N (dark blue).
6. Add the carbon and attach the hydrogens. Don’t worry about double bonds and lone pairs just yet.
7. There is a lone pair on the N. We can add this like any other atom on the periodic table. Left click on the "Lone Pair" box on the periodic table. Left-click and drag on the screen to attach the lone pair to the N. The lone pair appears as a dashed line.
8. In order to make the C=N double bond, move the "Draw" icon to the middle of the C-N bond (where the color changes from dark to light blue) and left click. Or simply click and drag the cursor from the C to the N. A double bond appears.
9. Close the periodic table window. Press the space bar. This centers your molecule.
10. Go to the "Build" pull-down tab and select "Add H & Model Build". This will clean things up a bit.
11. Go to the "Setup" pull-down tab and select "Molecular Mechanics".
12. Go to the "Compute" pull-down menu and select "Geometry Optimization". By default the "Polak=Ribiere" algorithm is selected and the "Options" box has 0.1 kcal/mol as the convergence criteria and 90 as the max cycles. Don’t worry about all this stuff. Maybe in a later class you will learn all about it. For now just click "OK"
13. You may see the molecule move around a bit. After a while it stops and the display line at the bottom of the screen says "Energy=__ Gradient=__ Converged=YES…" You have just done a simple geometry optimization. The computer has taken your guess for the structure of the molecule and moved the atoms around in order to get the lowest energy configuration. Play around with your molecule a bit.
14. You can add or remove labels by going to the "Display" pulldown tab and selecting "Labels". Choose "Symbol" from the "atoms" box for atomic symbols and "none" in the "atom" box to turn off atomic symbols.  will rotate your molecule out of the plane of the screen while rotates in the plane of the screen. will translate the molecule across the screen. At any point if you hit the space bar the molecule is centered in the screen.
15. Select the "Select" icon . Left-click on one of the H atoms which is attached to the C. The selected atom appears as a green circle and the Display line at the bottom of the screen tells you some things about the atom you selected.
16. Left-click on a carbon-hydrogen bond. The H-C bond appears green and the Display line at the bottom of the screen tells you the bond distance in A.
17. Left-click on an H atom and drag the cursor over to the N atom. The HCN bonds appear green and the bond angle is given below.
18. Right-clicking on an atom deselects that atom. Right-clicking anywhere off the molecule deselects all the atoms.
19. Go to the "Display" pull-down tab and select "Rendering". Play with the different types of displays. Notice that the lone pair of electrons on the N does not appear in any of the space filling models.
20. In order to start over, go to "File" and select "New". Do not save the changes.