Molecular Structure or "The Shape Molecules are In" Directions: Make a copy of this document and change the file name to “your last name, VSEPR Lab.” Place the document in the Google folder with your name on it. Follow each instruction to build molecular models and answer the following questions. Make sure your notes, comments, and answers are in a different text color. When you have finished with the lab questions attach a 12 page conclusion that summarizes and explains the main points of the lab.
1. After you have washed your hands, obtain your "atom" supply from Dr. Winston. Select one atom from your atom supply. Using four toothpicks, place them as far apart from each other around the atom. Remember, electrons have the same charge (negative) so it is their desire to be as far away from each other as possible.
2. The toothpicks represent single electrons as in carbon (four valence electrons) or if hydrogens come along and attach to each of the four toothpicks, then the toothpicks represent an electron pair shared between each hydrogen and carbon.
3. If you placed the toothpicks as far apart as they can be from each other in 3D you will be able to stand the atom on the table with no more than 3 toothpicks touching the table at one time. Try it, and if you can't readjust the toothpicks so that it can stand alone. Hint: the arrangement of electrons (toothpicks) should demonstrate threedimensional symmetry; i.e. it should look the same no matter how you rotate it.
4. The name of this arrangement is_tetrahedral_. Use a protractor to measure the angle between each electrons (toothpicks) to the correct number of significant digits. How many different angles can be measured? 6
Measure the angles and determine the average.114.4° If you had constructed the perfect Molecule what should the angle between any two electrons be? 109.5°
5. Try to rearrange your model to reflect the correct angle between each electron.
6. Use four more atoms from your supply to represent four atoms of hydrogen. Attach each hydrogen atom to the end of each toothpick on the first atom. As mentioned above the toothpicks now represent an electron pair. This represents a molecule of natural gas, methane (CH4). Keep this molecule for molecular shape comparison.
Call Dr. Winston over to check your work.
7. The next molecule's shape we will examine is for water. The central atom of water is the oxygen. Draw a Lewis dot structure for an oxygen atom below.
8. Use two different colors of toothpicks (a pen or marker will be sufficient to color code one set of toothpicks); one color for the paired electrons around oxygen and one color for the unpaired electrons. How many toothpicks are around the oxygen?4
9. Hydrogen bonds to the two unpaired electrons producing to share paired of electrons, each between H and O, or two covalent bonds. Draw a diagram of your gumdrop and toothpick molecule below.
10. When considering molecular shape only bonded pairs of electrons are considered. Remove the unbonded electrons and redraw your diagram from step 8, omitting the toothpicks that represented the unbounded pairs. Keep in mind that the angle between the two bonded pairs should be the same as it was in your drawing from step 8.
What shape does this molecule exhibit?Bent
11. Although the shape is not tetrahedral it does result from the tetrahedral arrangement of electrons around the oxygen. Is the angle between the hydrogens 90° or larger? What is the angle?Larger, 105.5°
12. Draw the electron dot configuration of water in this space. This should help you explain the larger than 90° angle between the two hydrogens.
13. Electron pair(s) that are unbonded act as repulsion areas to the other bonds. In essence they push the bonds away from their area. Would you expect the angle between the ...
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