Lewis Electron Dot Model

Lewis Electron Dot Model Lab

Background: Lewis electron dot structures are a useful and popular way in chemistry to visualize the bonding in molecules. Practice making Lewis electron dot structures by using bingo chips and cut out element symbols for the first 18 elements and then for a series of molecules.

In general, H atoms want to be surrounded by 2 valence electrons to attain the stability of He. All other nonmetal atoms want to be surrounded by 8 valence electrons, and thus should follow the octet rule. There are many exceptions to the octet rule, especially in atoms with d orbitals.

Procedure for determining Lewis Dot Model: 1. Count the total number of valence electrons available. To do this, determine the number of valence electrons supplied by each atom in the compound and add them up. a. For representative elements, the A-group number equals the number of valence electrons b. For polyatomic ions – add one electron for each unit of negative charge c. For cations – subtract one electron for each unit of positive charge 2. Draw the skeleton structure for the molecule, joining atoms by single bonds. a. The skeleton structure for X2 is X-X b. The skeleton structure for XY is X-Y c. For more complex molecules, more than one skeleton structure is possible. For the molecule XY2 the most likely structure is Y-X-Y Tips  Nature tends towards symmetry, so make your structures as symmetrical as possible  Hydrogen is never the central atom  Group VII halogens tend to be surrounding atoms rather than central atoms  Carbon tends to be a central atom 3. From the total number of valence electrons, subtract 2 for each single bond in the skeleton structure to determine how many are left to distribute. 4. Distribute the remaining electron pairs as unshared pairs around the atom in the molecule. Follow the octet rule, making sure each atom has a total of 8 electrons. (except H) 5. If this point is reached and there are too few valence electrons to give each atom an octet, a multiple bond is necessary. Multiple bonds involve sharing one pair of electrons for each bond.

Materials Element sheets Scissors Bingo chips Envelope Data tables

Pre Lab Cut out the 32 element squares from the 4 sheets of elements

Procedure Part 1- Elements 1. Locate Data Table 1 2. Record the family or group number for each element listed in Data Table 1. Refer to a periodic table to do this step. 3. List the number of valence electrons for each element in the next column of the Data Table 1. 4. Locate the element square for the first element in the table and set the square on a flat surface. Use bingo chips to place the correct number of valence electrons around the element. Follow the rules for writing Lewis Dot structures for the elements. 5. Draw the Lewis Dot Structure in the last column of Data Table 1. 6. Repeat steps 4-5 for each element listed in Data Table 1. 7. Answer Questions 1-4 in the Question section.

Part 2 – Covalent Compounds 8. Locate Data Table 2 9. Determine the number of valence electrons for each individual atom. Write each separate number in Data Table 2 (H-1, O-6 etc) 10. Add up the valence electrons for each atom and record the total number of valence electrons for the compound in the next column of the Data Table 2. 11. Locate element squares for each element in the compound and set the squares on a flat surface. Gather enough colored bingo chips to equal the total number of valence electrons. Use a different color for each element in the compound. 12. Use the bingo chips to place the correct number of valence electrons in the compounds. Follows the rules for atoms placement and electron placement described in the Background section of the lab. 13. Once the structure is made and all the rules have been followed, draw the Lewis Electron Dot Structure in the last column of the data table. 14. Repeat steps 8-12 for each compound listed in Data Table 2. 15. Put away all materials in designated place.

Data: Fill in the Data Tables

Questions: Answer on the back of your Data Tables. 1. Use the completed Data Table 1 to write a general rule relating the placement on the periodic table and the umber of valence electrons. 2. Are there exceptions to the general rule proposed in #1? Why does this exception occur? 3. Why can any atom have no more than eight valence electrons? 4. Write the Lewis Electron Dot structure for the following element. a. Barium, Ba d. Gallium, Ga b. Tin, Sn e. Potassium, K c. Radon, Rn f. Iodine, I Data Table 1: Elements Number of Valence Lewis Electron Dot Element Family or Group # Electrons Structure 1. H

10. Ne

11. Na

12. Mg

13. Al

14. Si

17. Cl

18. Ar Data Table 2: Covalent Compounds Valence Electrons Total number of Lewis Electron Dot Formula for Each Atom Valence Electrons Structure

2- Ex: SO3 S-6, O-6, 2 6+6+6+6+2=26

2. HCl

3. H2O

4. NH3

5. CH4

6. CH2Cl2

7. Cl2

8. HOCl

10. OH- + 11. H3O

Data Table 2: Covalent Compounds - Continued Valence Electrons Total number of Lewis Electron Dot Formula for Each Atom Valence Electrons Structure

+ 12. NH4

2- 13. SO4

14. N2

15. CHCl3

16. C2H6

17. CO2

18. CH3OH

19. H2O2

20. C2H4

21. C2H2 22. SO2