Libris Britannia 4/science library(b).zip/science library(b)/CHEMIST/VSDEM101.ZIP/README.TXT

Text File | 1993-10-24 | 10KB | 211 lines

                            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.