Learning How to Use CHIME

Once you have downloaded and installed the CHIME plug-in, go to http://www.chem.purdue.edu/gchelp/vsepr/index.html. You should read through the sections titled “What is VSEPR?”, “Rules”, “Counting Regions of High Electron Density”, and “Arranging Regions of High Electron Density” before starting this prelab. These sections are accessible through the links at the left of the screen.

In the “Arranging Regions of High Electron Density” section, familiarize yourself with CHIME. Do this by clicking on the electron-group arrangement name in the “best arrangement” column. Now (left) click and hold on the compound, move the mouse around (continue holding the left mouse button down). Get used to rotating the compounds around in order to get a better look at them. (Notice that the trigonal planar arrangement is so called because all the atoms are in the same plane and they are in a triangular shape with 120° bond angles all around the compound.) Play with rotating the compounds until you can easily identify the bond angles present. You can resize the compound within it's CHIME window by holding shift + left click and moving the mouse across the molecule. You can move the compound around within it's CHIME window by holding control + right click and moving the mouse around the window.

Now click on “Molecular Structures Based on VSEPR Theory” located in the menu at the left. Explore this section of the website to see what happens to the compounds when lone pairs replace atoms surrounding the central atom. Pay attention to any changes in the name for the electronic arrangement and/or the name for the molecular geometry.