Interactive Digital Overheads

This resource requires Adobe Flash Player to be run within a browser window, and it works smoothly on my modern system.

This review pertains only to the VSEPR subset of the interactive digital overheads, which can be accessed by clicking on "Molecular Structure" in the left hand menu of options and then on "VSEPR" or through the following link.

http://www.chem.arizona.edu/~jpollard/FlashComponents/VIP/vsepr/vsepr.html

The molecular geometries presented within this resource are consistent with descriptions presented in most high school and introductory college chemistry textbooks. This resource presents a 3-D representation of generic molecules that can be rotated along a set path, but does not appear to perform any calculations to generate the images.

The website contains many applets and are subdivided into various topics (atomic structure, chemical kinetics, chemical equilibrium etc). It also includes tools to make ones own representation and animation. Presented below is my evaluation of the applets contained in the chemical equilibrium sub-section.

The models under equilibrium represent different equations and include other concepts such as Gibbs free energy and combination of reversible equations with thermal energy. There is no documentation that describes the model or how to use it. Nevertheless, the interface is intuitive and is easy to use.

Each of the models has controls for many parameters, which allows the user to change at any time during the simulation, thereby allowing one to illustrate Le Chatelier's Principle. The changes in concentration are shown both by number of molecules and graphs. The strength of the model is in its ability to depict how various parameters are inter-related. The relationships between the parameters agree well with the underlying physical principles.

The underlying equations used to arrive at the graph and concentrations are not clear. The model has its limitations: rate of forward and backward reaction cannot be changed the range for the controls is narrow (e.g. up to 30 molecules for PCl3). None of these limitations are explicitly mentioned in the tutorial.

The models are predominantly in Flash there are also a couple of models in Java version. The models can be directly accessed using a web browser and is free to use. However, a high-speed connection will be required especially if the user would like to view multiple models simultaneously.

At the molecular level, the model does not accurately show size of the molecules, collisions between them and change in velocity with temperature.

Units are lacking for time, temperature, concentration and volume. Therefore, it may not be the best for quantitative analysis.

This review pertains only to the VSEPR subset of the interactive digital overheads, which can be accessed by clicking on "Molecular Structure" in the left hand menu of options and then on "VSEPR" or through the following link.

http://www.chem.arizona.edu/~jpollard/FlashComponents/VIP/vsepr/vsepr.html

The molecular geometries presented in this resource are consistent with those found in most high school and introductory college chemistry textbooks. Molecules with electron lone pairs on the central atom are displayed (e.g. trigonal pyramid, see-saw, or T-shape geometries), although there is no discussion about the specific effects of the lone pairs.

The VSEPR model used in this resource is sufficient for high school and introductory college chemistry courses. However, this resource does not display or measure bond angles, and it is difficult to visually identify any bond angle changes. There are no inputs into this applet - only the generic molecules in the resource are available for use.

The models available in this applet can be rotated, but only along a specific path that can be stepped forward and backward - the molecules cannot be freely rotated.

There are no links to scholarly materials from this web page. The tutorial assumes that the user is already familiar with the basic concepts. There are no suggestions with regard to pursuing the models at a more advanced level. In spite of its shortcomings, the model is valuable to grasp the basic concepts of chemical equilibrium. These models will be useful for both students learning chemical equilibrium and teachers introducing the concepts.