The World's Smallest Drop of Water

This is a simple demonstration of hydrogen bonding. Create a water molecule in the center of your screen. Now use the "insert" feature of the Spartan builder (lower right corner of window) to add 20-30 more molecules scattered around the screen. Turn the structure occassionally so these are not all created in one plane. This is the time to ask your students: Is this what water looks like?

Click on the  button and watch what happens. The force-field is parameterized to model hydrogen bonds. When the optimization is finished, examine distances between atoms. It should be easy to identify numerous H2O––H–O–H hydrogen bonds with distances of ca. 1.8 Angstroms.

 

The optimized structure will usually have a spherical shape. Note that this is NOT a dynamics simulation: The structure is static and meant to show structure only. Try adding a few ammonia molecules to the mix.

Change to space-filling view. What does this tell us about water?

For a simpler version, put only two water molecules on the screen and optimize the structure with force-field and then perform a geometry optimization calculation using the Hartree-Fock method and the 3-21G basis set. The water dimer has been well studied and easily shows hydrogen bonding.