Molecular Geometry and Bond Angles Lab
This activity will introduce you to a molecular geometry program called
ChemSketch. This program will allow you to build various models of molecules
with single, double, or triple bonds. You can also determine bond angles for
specific atoms in the molecule. Follow the instructions carefully. When you are
finished with the molecule, name it and save it for future use.
Steps for using Chemsketch
1.
Find Chemsketch by clicking on the start button, locate all programs. Find
ACDLABS 11.0 and click on ChemSketch.
2.
On the toolbar, click on the
will open the 3D view.
3.
On the lower portion of your screen, you should see ChemSketch, Copy to
3D, and 3D view. Click on ChemSketch.
4.
You are now going to build a simple carbon tetrachloride molecule. In the
top left hand corner, click on Structure. Now, on the left hand side of the
screen, click on “C”. Click once in the work area. You should see a
methane molecule appear. Do not despair!! This is supposed to happen.
Next, click on “Cl”. Click once in the work area. You should see HCl
appear.
5.
You are now going to place the bond. Place the cursor on the Cl atom.
Click, drag, and release the mouse button on the “C” atom. You have
now created CH3Cl. Each time you click on the work area, you will drop
the last element selected. Click again on the work area and you should
see another HCl appear. Use the same process to place the bond
between the Cl atom and the C atom. Pay attention to the number of H’s
after each bond placement. Continue doing this until you have placed
four Cl atoms around the C atom. You now have a rough sketch of
carbon tetrachloride.
6.
Now go to Tools and choose 3D structure optimization. On the lower left
toolbar, click Copy to 3D. Your newly formed molecule should appear.
7.
Click the
tab on the right side of the bar. This
icon to produce a ball and stick model of the molecule.
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8.
To minimize the geometry, click the
icon near the top right hand
corner. Make sure the
icon is on. This allows rotation of the
molecule. It is located on the right side of the toolbar. Click and drag the
molecule to rotate the molecule in three dimensions.
Next, you will learn the process for measuring bond length and angles.
9.
Click on the
icon, then click on the carbon atom. The carbon atom
should change color. Hold down the shift key and click on a Cl atom. A
window should pop up that shows the C-Cl bond distance. This program
measures bond length in angstroms (Å). Your book may use nanometers
(nm). The relationship between angstroms and nm is 1 nm = 10 Å.
Convert your answer and write it in the space provided. Measure bond
lengths for all four C-Cl bonds.
Bond distance for C-Cl
1.________________
2.________________
3.________________
4.________________
A
A
A
A
________________nm
________________nm
________________nm
________________nm
How do the measurements for the bonds compare?
____________________
Why?
_________________________________________________________
_________________________________________________________
10.
Next, click on the
icon. This allows you to measure the bond angle.
Predict what you think the bond angle will be, and write your answer
below.
Cl-C-Cl bond angle ______________°
11.
Click on a Cl atom. Hold down the shift button and click on the C atom
and another Cl. You must hold down the shift key until you have clicked
both atoms. A pop up window should appear with the bond angle.
Record this measurement below.
Cl-C-Cl bond angle 1.________________°
2.________________°
3.________________°
4.________________°
$$$There are 6 different angles.
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How do the bond angles compare?___________________
Why?_______________________________________________________
____________________________________________________________
What is the shape of the molecule?_______________________________
Does this shape appear to be correct for a molecule with this geometry?
______________
Why or why not?______________________________________________
____________________________________________________________
12.
Now spend some time with the following display option buttons:
13.
Try the two different view buttons.
14.
To change the color of the background, click on the
icon.
Write out the chemical formula for carbon tetrachloride.
__________________
Do a little research and determine some uses of this compound.
____________________________________________________________
____________________________________________________________
____________________________________________________________
15.
Going further: Now you need to build some molecules of your own using
ChemSketch. Build molecules for the following shapes. When finished,
print. Guess a name for your molecule and write it down below. There is
a feature in ChemSketch that will give you the correct name of a
molecule. On the bottom left toolbar, click on ChemSketch.
1.
Trigonal planar
2.
Pyramidal
3.
your choice
If using multiple bonds, you can only view those in the wireframe
mode.
Draw the Lewis Structures for the previous molecules. Do the structures match
the shape of each molecules?
If time allows, fell free to go back to the ChemSketch view and play around!!
©2011 University of Illinois Board of Trustees • http://islcs.ncsa.illinois.edu/copyright
©2011 University of Illinois Board of Trustees • http://islcs.ncsa.illinois.edu/copyright