Contents:

• General Information
  • Roles & Responsibilities
  • Tasks and Expectations
  • Goal and Specific Objectives
• Reading Assignment
• Scigress Resources
• The Group Project
• Resources
• Group Assessment
• The Report
• Documenting your Resources
  • CD-ROMs
  • WWW Sites & E-journals
• Other Useful Links

General Information:

• Manager will direct the sequence of events, keep the team "on track", make sure everyone participates ("Holly, what do you think about this?") and watch the time spent on each step.
• Recorder/ Reflector will act as scribe for the group recording the group's answers on a separate sheet of paper and complete the group assessment — using input from the entire group.
• Resource manager/checker will obtain resources, and check for understanding ("Do we all understand this?") and will make sure all members of the group agree on plans and actions ("Are we in agreement?")
• Technician/energizer will perform technical operations (operate the computer, calculator, etc.), energize the group when motivation is low ("We can do this!", "That's a GREAT idea!", "So here's what we've decided …") and summarize the group's discussion and conclusions -- i.e. the technician/energizer writes the group summary!

• Task:
  • Individual — each member of the group will perform all specific operations with at least one of the assigned molecules
  • Group — as a team arrive at a consensus of the correct 3-D structure and geometry for each of the assigned molecules
• Expected Criteria for Success: Everyone must be able to explain how the group arrived at each conclusion.
• Individual Accountability: There will be a quiz on this material on Friday, November 11.
• Expected behaviors: Active participation, checking, encouraging and elaborating by all members.

• Create shapes similar to molecules with two, three, four, five and six bonding atoms using balloons.
• Review the principles of VSEPR theory using the Valence Shell Electron Pair Repulsion tutorial at the University of Sheffield.
• Assign a geometric shape to a series of molecules by comparing the "flat" Lewis dot structures to the balloon shapes.
• Check the structure assignments of the molecules using the Interactive VSEPR calculator.
• Determine bond angles and bond distances using Scigress.

Reading Assignment: You should review the following as you work through this project.

• You should be fairly comfortable with the procedure for drawing Lewis dot structures. Professor Silberberg outlines drawing Lewis structures in section 1 of Chapter 10 (pp 366-375), Chemistry, The Molecular Nature of Matter and Change.
• The basic principles of Valence Shell Electron Pair Repulsion theory (VSEPR) are discussed in section 3 of chapter 10 (pp 375-385) of Chemistry, The Molecular Nature of Matter and Change.
• Professor Silberberg discusses the elements of Valence Bond/Hybrid Orbital theory in section 1 of chapter 11 (pp 399-406) in Chemistry, The Molecular Nature of Matter and Change.

Scigress Resources:

• This activity assumes that you are already familiar with the basics of using Scigress/CAChe. For a quick refresher, check the following on line tutorials:
  • Starting CAChe (AKA Scigress)
  • Using the User Interface Or  Click Here to use the Flash Tutorial
  • Building small molecules
  • Viewing and manipulating structures
  • Optimizing the geometry with Mechanics and MOPAC
  • Measuring bond angles and bond distances.

The Group Project

• Part I -- Getting Ready With Financial assistance from the whole group the Resource Manager will procure a bag of balloons. The round kind are best. They do not have to be big, but you will need about fifty (50). Now everyone has to help blow up 20 of the balloons -- about the same size. You'll use the balloons to approximate the geometries of the five basic shapes that molecules tend to assume. The really cool part is that the balloons assume these shapes naturally. Once you've finished inflating the balloons (and everyone has recuperated), take two of the balloons and join them at the knotted ends. You will find that joining groups of three, four, five and six balloons produces some interesting shapes. You may have seen these before; you may even know the names. However, at this point give each shape a name that the whole group thinks is appropriately descriptive. The recorder should be keeping a record of this discussion as you will want to turn in this information with your "report".

• Let's Go Surfing -- to Sheffield Visit Mark Winter's Valence Shell Electron Pair Repulsion (VSEPR) tutorial at the University of Sheffield, in Sheffield. England (BTW -- Mark Winter is also responsible for WebElements). Study all of the examples of the different kinds of shapes of molecules (in the left hand frame). It will pay to be thorough. Examine each example, make notes (or print the frame) and be sure to examine the structure using one of the visualization tools. Keep a record of what you learned as you might want to refer to it again.

• Back to the drawing board The list below contains four different molecules which are representative of the most basic geometries. Begin by drawing Lewis structures of each and match the flat Lewis structure with the best balloon shape. Confirm your prediction using the Interactive VSEPR Calculator. How did you do? Refine your structures until you feel comfortable with your results. Draw a picture of the 3-D structure.
  • BCl₃
  • CF₄, CF₃Cl
  • AsCl₅
  •  SF₆

• Claymation -- a cartoonist's view of hybrid orbitals At this point the most important thing about hybrid orbitals is that you develop a good conceptual understanding of the idea so that you can apply it to specific molecules. You will find the material in the text clear and fairly easy to understand.  There are several WWW sites that have material on Valence Bond Theory and Hybrid Orbitals.  After reviewing one of these resources, you should be able to describe the orbital hybridization on the central atom in each of the four molecules which you have examined thus far.

• Scigress - aka CAChe  
  • Open the WorkSpace in Scigress and build each of the molecules for which you drew Lewis structures and 3-D pictures.
  • Three cautions:
    • Some of these elements will not be in the Atom Type Box  .  You will need to select it from the Periodic Table.
    • Make sure the hybridization on the central atom matches the hybridization you assigned in the previous step. The hybridization of the bonding atoms should be sp³-tetrahedron.
    • The Beautify|Comprehensive step might be helpful. For this set of molecules it will assign the correct hybridization on the central atom and get the geometry somewhat symmetrical.
  • You should have a folder called Molecules in the My Documents area of your computer. If you are using one of the computers in the campus labs, store your Scigress files on a flash drive. It would be a good idea to create a folder called Molecules. Create a folder sub-folder called Balloon Project in your Molecules folder.  Store each of the molecules you build in the Balloon Project folder. This all sounds a bit obsessive, but it will make it much easier to finds things later.  Name each file according to the formula for the molecule (BCl3, AsCl5, etc.).
  • Optimize the geometry using MOPAC-AM1 (for BCl₃, CF₄, CF₃Cl) and MOPAC-PM3 (for AsCl₅ and SF₆).
    • Select Experiment|New  
    • In the Property of: box, select chemical sample.
    • in the Property box, select optimized geometry.
    • In the Using box select AM1 geometry (or PM3 geometry)
  Since you've been working so hard -- blowing up balloons, building molecules in Scigress and surfing the web, you might feel like you deserve a rest. So ... DO IT! Be sure you have recovered because you'll have to blow up a few more balloons!

• Part II -- Blow up a few more balloons! You can use the "old" balloons, but you'll want to disassemble them. You'll need some more: three more the same size and 12 more that are a little bigger. Remember when you were drawing Lewis structures how some molecules had lone pairs? Well, the slightly larger balloons represent the lone pairs. Once your group has all the necessary balloons, you can start assembling them. When chemists talk about molecular geometry they use a shorthand. The letter A represents the central atom (the knots of balloons in our case); the letter B represents the bonding atoms (the smaller of the balloons) and the letter E represents the lone pairs (the slightly larger balloons). So, when you assemble the balloons this time, you want to make each of the combinations listed bellow. This is why group work is so helpful -- and maybe even fun!
  • AB₃E       AB₂E₂       ABE₃
  • AB₄E       AB₃E₂      AB₂E₃
  • AB₅E       AB₄E₂
  • As with the first set of balloon shapes, give each one a name. It's OK if you use the "Official" name; or feel free to make one up. The important thing is that you see how swapping a lone pair for a bonding atom changes the shape of the molecule -- ever so slightly!
• Let's Go Surfing --If you think you might need a refresher, you can visit Mark Winter's Valence Shell Electron Pair Repulsion (VSEPR) tutorial . Or, try out the VSEPR module, created by John J. Nash at Purdue University.  It has a summary of the VSEPR rules along with some practice problems.  You also can compare two structures.
   
• Back to the drawing board -- again! By now your team should be working very well together. There are eight molecules listed below. You probably already figured out that you will want to draw Lewis structures of these molecules. ... And if you are trying to stay one step ahead, you might have also figured out that they somehow correspond to the eight different combinations of balloon structures which you just created. So...
  • Draw the Lewis structures.
  • Match each Lewis structure to one of your balloon creations and name it.
  • Confirm your prediction using the Interactive VSEPR Calculator. How did you do? Refine your structures until you feel comfortable with your results.
  • When you feel certain that you have the best arrangement, draw the 3-D projection.
  • Describe the orbital hybridization on the central atom in each of these molecules.

Second set of Molecules:
• TeF₄^2-       OF₃⁺       ICl₂ ^-
• H₂O          SF₄
• SF₅^-           IF₃
• Scigress - aka CAChe  
  • Open the WorkSpace in Scigress and build each of the molecules for which you drew Lewis structures and 3-D pictures.
  • Some cautions:
    • You may need to select your atoms from the Periodic Table.
    • Adjust the hybridization on the central atom to match the hybridization you assigned in the previous step. The hybridization of the bonding atoms should be sp³-tetrahedron.
    • For the anions (TeF₄^-, SF₅^- & ICl₂^-) and cations (OF₃⁺ ), calculate the formal charge on the central atom.  Make sure you set the atom charge. . For details see the tutorial on building ozone (opens in a new window). 
    • Fix your by using Beautify|Geometry.  Warning!! DO NOT USE Beautify|Comprehensive!! It will give you a very crazy picture!
  • Save each molecule in the Balloon Project folder.  Name them according to the formula (OF3, SF5, etc.)
  • Optimize the geometry using MOPAC-PM3.
    • Select Experiment|New  
    • In the Property of: box, select chemical sample.
    • in the Property box, select optimized geometry.
    • In the Using box select PM3 geometry
  • Measure the bond angles and bond distances on each molecule.  For a refresher, check the directions from Modeling Exercise # 2.

• A Chance for some Bonus Points (and everyone loves Bonus Points!) Chemists (Inorganic chemists in particular) are always trying to make new molecules to test theories like VSEPR!  In 1991, a group from Rocketdyne, McMaster University and E. I. du Pont successfully prepared and characterized the Pentafluoroxenate(IV) anion, XeF₅^-.  The paper was published in the Journal of the American Chemical Society (1991, 113, 3351-3361).  Their studies showed that the ion  fits the AB₅E₂ geometry.
  • Using the same strategies you used in Part II, assemble the balloon combination for AB₅E₂; give the shape a name.
  • Draw the Lewis structure for XeF₅^-.  Do you get a AB₅E₂ arrangement as well?
  • Check the correct geometry for XeF₅^- using the Interactive VSEPR Calculator and refine the structure as needed.
  • When you feel certain that you have the best arrangement, draw the 3-D projection.
  • Describe the orbital hybridization on the central atom in  XeF₅^-.
  • If you try building and optimizing this molecule in Scigres you will get some funny results!  The balloons are better at describing the geometry!

---

Resources

• DrawingLewis Structures
  • Professor Silberberg discusses Lewis structures in Section 1 of Chapter 10 (pp 363 - 373) in Chemistry, The Molecular Nature of Matter and Change.
  • Formal Charge -- see pages 368 - 369 of your text (Chemistry, The Molecular Nature of Matter and Change, by Martin Silberberg) 
  • Resources on VSEPR
  • Mark Winter's Valence Shell Electron Pair Repulsion (VSEPR) tutorial at the University of Sheffield, in Sheffield. England
  • The Sheffield ChemPuter.
  • The VSEPR tutorial, created by John J. Nash at Purdue University.
  • Molecular Geometry -- Molecules in motion
  • In your text
• Resources on Hybrid Orbitals-- these are listed here for you to use as helps.  Each of you will find a different one to be the most helpful.  and-- of course -- you might find something even better!  If you do, please let me know!
  • You can find a nice review at the Organic Chemistry page from Towson State University.
  • In your text.
•  CAChe (Scigress) Tutorials
  • Check the UPJ Chem Department on-line CAChe Tutorials
  • Review the Scigress/CAChe  exercises for General Chemistry:
    • Exercise # 1
    • Exercise # 2
    • Exercise # 3

The Finished Product

No doubt you're wondering what you'll have to submit -- for graded work -- after all, you do want to receive credit for all of this work:

• Summarize: In 2 to 3 (well-organized) paragraphs describe what you did with the balloons in Part I and Part II.  Describe the shapes that you created and any impressions that you got as a result (organization, grammar and spelling count!).
• For each of the molecules in the first part:
  • The Lewis structure
  • The name you gave it
  • The three dimensional structure using VSEPR
  • Did you have to change your original prediction as a result of using the VSEPR calculator?  Was this helpful?
  • Describe the orbital hybridization
  • The bond angles and bond distances measured using Scigress
  • (Optional: Copy and paste the optimized structure from Scigress; show bond angles as with Exercise # 2.)
• For each of the molecules in the second part:
  • The Lewis structure
  • The name you gave it
  • The three dimensional structure using VSEPR
  • Did you have to change your original prediction as a result of using the VSEPR calculator?  Was this helpful?
  • Describe the orbital hybridization
  • The bond angles and bond distances measured using Scigress
  • (Optional: Copy and paste the optimized structure from Scigress; show bond angles as with Exercise # 2.)
• For the BONUS molecule:
  • The Lewis structure
  • The name you gave it
  • The three dimensional structure using VSEPR
  • Did you have to change your original prediction as a result of using the VSEPR calculator?  Was this helpful?
  • Describe the orbital hybridization
• Summarize what you learned in a well organized paragraph (grammar and spelling count!).
  • New information
  • Things that still cause you difficulty
  • List any difficulties you encountered while using Scigress/CAChe.
• Group Assessment -- you can download a copy from the web (in MSWord format).
• Lay-out and appearance:  This is a "report" of sorts.  Start with the summary of what you did with the balloons. Tell a brief "story".  Then include the work for each of the molecules in the first part.  It would be best if you used a separate page for each molecule (that way, if you divided the responsibilities for the molecules among different people in your group, each person can submit her or his page). Please no more than three molecules to a page. It makes it more difficult for me to read (quickly) if you put too much on one page!  The work for the molecules in the second part should follow; again use a separate page for each molecule.  The summary should go at the end (on a separate sheet) followed by the Group Assessment which you can down-load (MSWord format) and complete.
• The assignment is worth 60 points, counts as 3 quiz grades and is Due in class, Wednesday, November 8, 2011.