Note: A number of the links in this document provide a hint or additional information if you hover over them.


The purpose of this dry lab is to help you practise:

The applet, (link below; read this first), selects semi-randomly from a data base of simple compounds and ions, and allows you to construct Lewis structures, where a bond between two atoms results from the sharing of a pair of valence shell electrons. Such bonding can be described mathematically using the wave-mechanical treatment known as "valence bond theory" which was initially developed for this purpose.

While there are other kinds of bonds, for example, multi-centre bonds which are perhaps better described by molecular orbital theory, and a variety of other interesting exceptions, the first step in describing the bonding in most molecules or molecule-ions (complex ions) involves selecting possible structures based on two-centre two-electron bonds.


Start the applet - it will appear in a pop-up window. (You may need to enable pop-ups if your browser is blocking them. You may also need to allow the applet to run.)

Click "pick problem" to have the applet select a molecule, ion, or ionic compound for you to work on. The choice is made randomly from a database of around 60 species. Do 10 for inclusion in your report, and more if you want to. It is also possible to enter your own for more practice - see the notes below for more information.

The formula of a molecule, ion or ionic compound will be displayed in the box next to the "pick problem" button. If the problem is an ionic compound, you must recognize this, and just do the complex (polyatomic) ion. The monatomic counter-ion(s) must not be used.

There are two ways to proceed:


For each of the 10 structures, your report should contain the following items:

  1. A clear hand-drawn copy of the Lewis structure as it was displayed on the computer screen when it was successfully completed.In addition, do not forget to mention any counter-ions which are part of the compound which you were working on.
  2. Specify and draw the prototype "electron pair" geometry which goes with the "steric number" you have arrived at. Specify the corresponding "hybridization", and the observed "molecular geometry". There may be helpful diagrams in the two questions posed by the applet after you have constructed the Lewis diagam. Marks will be awarded for artistic merit!
  3. Give the answers to the two questions.