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1. Module 2 Intro

1.10. Page 2

Lesson 2

Module 2—Chemical Compounds

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Read page 91 in your textbook. Copy the five statements on VSEPR theory listed at the bottom of the page. Save a copy of these statements in your course folder. You may wish to refer back to this list as you complete the next activity or later when you are reviewing the material from this lesson.

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Using VSEPR Theory to Predict Molecular Shape

In this activity you will draw Lewis formulas for chemical compounds and then use the information to consider the three-dimensional shape of these molecules.

Step 1: Print a copy of the handout “Using VSEPR Theory to Predict Molecular Shape.”

Step 2: In the second column on the table, write the Lewis formula for beryllium dihydride, BeH2.

Step 3: Use the Lewis formula drawn in step 2 to complete columns 3 through 5.

central atom: the atom in a molecule that has the most bonding electrons and, therefore, is likely to form the most bonds

Step 4: Use the information from the Lewis formula to determine the distribution of electron pairs in three dimensions around the surface of the central atom, Be. A central atom is the atom in a molecule that has the most bonding electrons and, therefore, is likely to form the most bonds.

Record your answer in column 6 using a term that describes the shape of the molecule around its central atom. You may wish to use a molecular model kit or other materials to represent the atoms involved. If you are using other materials and need assistance, print a copy of the handout “Representing Atoms Using Models” and refer to it as needed.

Step 5: View the video BeH2 to confirm the shape and representation you have determined.

Step 6: Draw the stereochemical formula for BeH2.

Step 7: Repeat steps 2 through 6 for boron trihydride, methane, and ammonia, which are listed in the first column on your table.

Boron trihydride, BH3

Methane, CH4

Ammonia, NH3

Step 8: Read pages 92 and 93 in your textbook. Use the information in the textbook to check the accuracy of your table. If you encounter any difficulties, contact your teacher.

Step 9: Repeat steps 2 through 6 for the remaining substances listed in your table. Use your knowledge of the VSEPR theory to predict the effect that a multiple bond would have on a central atom. To check your work use the information on pages 92 to 95 in your textbook and use the videos listed below for the molecules.

Water, H2O

Hydrogen chloride, HCl

Oxygen, O2

Nitrogen, N2

Carbon dioxide, CO2