CHEMISTRY

Part 2: Describing Molecular Structures

5. Using Table 1 as a guide, label and organize the atoms of the molecular modeling kit. See Figure 12.

Figure 12. Organized molecular modeling kit.

Note: You might not use all of the pieces included in the modeling kit during this exercise.

6. For each molecule listed below, you will: 1- calculate the number of valence electrons, 2- draw the Lewis structure(s), 3- upload an image of the VSEPR model, 4- list the number of bonds and lone pairs surrounding the central atom(s), and 5- identify the structure geometry; or identify multiple geometries if there is more than one central atom.

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Experiment Molecular Modeling and Lewis Structures

7. Use the periodic table in Figure 2 of the Background to calculate the number of valence electrons in CCl4. Click here to download a printable copy of the periodic table. Record in Data Table 1 of your Lab Report Assistant.

8. Draw the Lewis structure for CCl4 and insert into Data Table 1. Ensure that the features of the molecule are large enough and clear enough for your instructor to grade. Refer to the background for step-be-step instructions on drawing Lewis structures.

Note: To draw the Lewis structure, either use a computer drawing program, such as Power Point, or other computerized drawing tool and cut and paste into Data Table 1, or draw by hand, scan, resize, and then insert into Data Table 1, or draw by hand and take a photograph, resize and then insert into Data Table 1. Refer to the appendix entitled, “How to Label an Image” for guidance Refer to the appendix entitled, “Resizing an Image” for guidance. If resonance structures exist for any of the molecules, make sure to draw all of the structures.

9. Use the molecular modeling kit to build CCl4. Ensure that the appropriate atoms are used, as described in Table 1. The completed molecule should have no “open” or unfilled holes.

10. Place the molecular model of CCl4 on a white sheet of paper with your name and the date written on it, take a photograph of the model, as shown in Figure 13. Resize and insert the image into Data Table 1.

Figure 13. NCH3CH3CH3: molecular model with student name and date.

11. Determine the number of bonds and lone pairs that surround the central atom. Record the data in Data Table 2 of your Lab Report Assistant.

Note: If there is more than one central atom, identify each atom and list the number of electron clouds that surround each.

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Experiment Molecular Modeling and Lewis Structures

12. Use Figure 11 to determine the name of the geometric structure for ClC4. Structure names include: linear, bent, trigonal planar, trigonal pyramidal, tetrahedral, square pyramidal, and octahedral. Record the name Data Table 2.

13. Repeat steps 5-12 for the remaining molecules.

Hints:

● Some molecules have more than one central atom: multiple geometries will need to be described.

● Some molecules have a charge: draw brackets and indicate the charge in the Lewis structure.

● Some molecules have resonance: draw all of the forms for the structure.

● Most, but not all, of the molecules fulfill the duet and octet rules.

14. When you are finished uploading photos and data into your Lab Report Assistant, save and zip your file to send to your instructor. Refer to the appendix entitled “Saving Correctly,” and the appendix entitled “Zipping Files,” for guidance with saving the Lab Report Assistant in the correct format.

Cleanup:

15. Return all items to the kit for future use.

Questions A. Which, if any, of the molecules in Exercise 1 had resonance structures? How many resonance

structures did each molecule have?

B. Both chlorine and fluorine are represented by a green modeling piece that has 4 holes. Is using the same piece for two different atoms acceptable? Why or why not?

C. List all of the possible geometric structures of a molecule that contains two atoms.

D. Explain why only the lone pairs on the central atom are taken into consideration when predicting molecular shape. What molecules from the lab activity are exceptions to this?

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