VSEPRplex TUTORIAL VSEPRplex Demo is copyright 1993 by Christian Fielding, Shawn Leclaire, and Peter Zion. All rights reserved. VSEPRplex Tutorial is copyright 1993 by Christian Fielding, Shawn Leclaire, and Peter Zion. All rights reserved. This VSEPRplex demo package allows you to sample and appraise the software, prior to making a financial commitment. The package may be freely duplicated and distributed. All other rights concerning the package are reserved. VSEPRplex was created by students for students. To contact the authors, write to: VSEPRplex c/o Peter Zion 43 Newcourt Place Kingston, Ontario K7M 6Y1 CANADA ABOUT VSEPRplex VSEPRplex is a molecular modelling set, which uses the computer to assist studies in VSEPR theory. The title, "VSEPRplex", is a "portmanteau word" in that it blends the sounds and combines the meanings of two words, "VSEPR" and "perplex". Their joining suggests the purpose at hand: to help students overcome the visual and conceptual perplexities involved in learning VSEPR theory. The main reason why students have difficulty with VSEPR theory is that the traditional teaching aids have never been very effective. The concept of three-dimensional bonding is not easily conveyed, and blackboard illustrations and physical modelling sets do not meet the challenge well. Two-dimensional drawings are particularly poor, because they lack accurate proportion and perspective, and often fail to reveal the entire molecule. Physical modelling sets are also frustrating, because they limit the number of molecules that can be assembled, and forfeit or compromise important attributes, such as atomic radii, bond angles, and bond distances. VSEPRplex overcomes these kinds of problems in two ways. First, the program frees molecular modelling of all physical restraints by using a "virtual" process -- it creates simulations that exist only in the computer. Virtual models are capable of exceptional detail, accuracy, and self-evidence. Second, VSEPRplex does not "retrieve" molecules from a database; rather, it mathematically derives its models from first principles of physics and chemistry. This deductive functioning of the program permits a considerably greater number of molecules to be explored than would otherwise be possible. Modelling with VSEPRplex is powerful, but the process is easily mastered. The student assembles a molecule by selecting elements from a periodic table, and the program then performs a reaction. Four models of the molecule (skeletal, Lewis, vector, and space-filling) then become available. These models have unique qualities, and when considered together, they provide a solid representation of the molecule. Perception can be further enhanced by performing "real-time" rotations on the three-dimensional models, and by adjusting various model attributes. Models are accompanied by text displays, which tutor the student in structural derivation procedures. VSEPRplex provides the student with the opportunity to realize both visual and conceptual proficiency with VSEPR theory. The aim is to make molecular bonding something that the student truly understands. INSTALLATION In order to use the VSEPRplex demo, a computer running Microsoft Windows Version 3.1 (or newer), a mouse, a VGA card (or better), and a colour monitor are required. To install the VSEPRplex demo, insert the program disk into the appropriate disk drive. Start Windows, and then select the Run... Item from the Program Manager's File Menu. Type a:install (or b:install, as the case may be) in the Command Line prompt box, and then click on the OK Button (using the left mouse button), or press the Enter Key. When the installation program asks where to store the VSEPRplex demo files, type the appropriate drive and path name, and then click on the OK Button. If the directory specified does not already exist, the installation program will create it, and copy the demo disk to this location. The installation program will then create a Program Manager group entitled "VSEPRplex Demo". A VSEPRplex Demo application icon will be created in this group. TUTORIAL To start the VSEPRplex demo, start Windows, and then double- click on the VSEPRplex Demo group icon (using the left mouse button). When the VSEPRplex Demo group window opens, double- click on the VSEPRplex Demo application icon. When an About Window opens, click on its OK Button. The molecule to be modelled is water (H2O). This demo does not permit you to assemble the many other molecules predicted by VSEPR theory -- you must purchase the VSEPRplex package for this. The assembly begins in the Formula Window, where a portion of the periodic table of the elements is found. The table is composed of a series of buttons, each representing a specific element. Click twice on the Hydrogen Button (using the left mouse button) to insert two atoms of hydrogen into the formula. Click once on the Oxygen Button to insert one atom of oxygen. The formula should read H2O. Click on the Oxygen Button once again, but this time using the right mouse button. This will delete one atom of oxygen from the formula. Any number of atoms can be deleted in this manner. A deletion can also be achieved by clicking the left mouse button while holding down the Shift Key. Since a water molecule actually does contain one atom of oxygen, insert it in the formula as before. Ionize the molecule by clicking the Positive Ion Button one or more times. Notice that the formula now carries a charge. Since a water molecule carries no such charge, eliminate the ion by clicking the Negative Ion Button the appropriate number of times. Use the mouse to select the Element Attributes Item from the Texts Menu. The important element attributes for hydrogen and oxygen -- attributes such as covalent radius and electronegativity -- will appear in the Text Window. This is the essential data that the program uses to make all structural calculations. Click on the React Button. Since H2O is a valid combination, the reaction will succeed, and structural calculations will automatically be displayed in the Text Window. These calculations outline how the shape of the molecule was determined. Had the formula been invalid for reasons of chemistry, a message indicating the problem and its solution would have appeared. Models of the water molecule can now be viewed in the Model Window. Select the Skeletal Item from the Models Menu to access a skeletal model. Access a more informative model by selecting the Lewis Item. The Lewis model is also two-dimensional, but unlike the skeletal model, it reveals lone pairs, as well as the allocation and types of bonds in the molecule. Compare the Lewis model to the structural calculations shown in the Text Window. The final two models (vector and space-filling) are three- dimensional. Select the Vector Item from the Models Menu to display a vector model of the molecule. This model plots atomic bond distances as vectors, and highlights the geometric facets of the molecule. A vector model effectively illustrates the structural classification of the molecule. Rotate the model by positioning the pointer over the Model Window. The "arrow" becomes a "hand". While holding down the left mouse button, drag the pointer over some distance. The vector model will dynamically change its orientation. Experiment with different rotations to explore the structure of the molecule. Select the Hide Virtual Sphere Item from the 3-D Model Settings Menu to remove this sphere from the model display. As well, select the Hide xyz-Axes Item to remove the xyz-axes. This simplifies the display in the Model Window, and allows rotations to operate with greater speed. A molecule's shape is classified by geometric orientation and more specifically by molecular geometry. The vector model for water currently illustrates the molecule's geometric orientation as being "Tetrahedral". Select the Molecular Geometry Item from the Shape Classification Sub-menu of the 3-D Model Settings Menu. The model now highlights molecular geometry by distinguishing (in gray) all vectors joined to lone pairs. The molecular geometry is clearly "Angular". Select the Space-filling Item from the Models Menu to access a space-filling model. This type of model preserves bond distances, but does not plot them as vectors; instead, it plots the atoms of the molecule. The rotations of the previous model are maintained. Rotate the model to explore it completely. The space-filling model continues to highlight molecular geometry (in this case, by hiding lone pairs). To make it once again emphasize geometric orientation, select the Geometric Orientation Item from the Shape Classification Sub-menu of the 3-D Model Settings Menu. Lone pairs now appear as gray spheres. For space-filling models, a "volume-fill" setting can be changed. The default volume-fill is "coloured". Experiment with other volume-fills (transparent, solid, and shaded) by selecting their items from the Volume-fill Sub-menu of the 3-D Model Settings Menu. This completes the modelling process for water. To clear this formula and its accompanying displays, click on the Clear Button in the Formula Window. The authors thank you for trying the VSEPRplex demo, and ask that you pass it around.