Summer Research Program for Science Teachers

Shanti Rywkin  

The School for Legal Studies, Brooklyn

2000

How are the properties of covalent compounds influenced by chemical bonding?

Grade:               Regents Chemistry

Materials::            Periodic Table, Computer facilities and familiarity with a molecular builder program.

Overview:            This lesson plan utilizes the Spartan molecular builder program. [9-12 Content Standard E- Understandings about science and technology]Students usually have   difficulties connecting the concepts of bond strength with chemical reactivity and the effect of lone pairs of electrons on the geometry of common organic molecules.

Purpose:            Students can use the following hands on activities to visualize the relationship between bond strengths and chemical reactivity for saturated and unsaturated hydrocarbons and examine the geometries of CH4, NH3 and H2O.

Objectives:            Students will be able to:

1.                  Use the molecular structures of ethane, ethene, and ethyne to observe and record the bond lengths of single, double and triple bonds. [Content Standard Unifying Concepts- Change, constancy, and measurement]

2.                  Make predictions of the bond strength and chemical reactivity of the saturated vs. unsaturated hydrocarbons. [Content Standard Unifying Concepts- Models and explanation]

3.                  Use the molecular structure of methane, ammonia and water to observe the effect of lone pairs on bond angles and shapes of molecules.

4.            Make predictions of the molecular shapes of similar structures.

Activity I:        To be done with a partner

Click on the file toolbar and using the builder kit, prepare and minimize the saturated hydrocarbon C2H6.

Select view from the build menu and view the molecule in the wire model.

Record how many single, double, or triple bonds are present.

Select measure distance from the geometry menu and measure and record the distance between each carbon atom.

Repeat the above procedure for the unsaturated hydrocarbons C2H4 and C2H2.

Prepare a printout of the molecules arranged in increasing bond lengths starting with the smallest. Store this information on a disk.

Based on the bond lengths, prepare a printout of the molecules arranged in order of increasing bond strengths, starting with the smallest

Prepare a structure of C6H6 and make a prediction of the type of C-C bonds present in this compound.

Questions:     Based on the bond strength, which bond is easier to break?

Which compound is least reactive with H2?

Midpoint   Conclusion:      Write a short paragraph to describe the differences between the saturated and unsaturated hydrocarbons. [Teaching Standard B- Orchestrate scientific discourse]

Activity II:       To be done with a partner

Click on the file toolbar and using the builder kit, prepare and minimize the compounds CH4, NH3 and H2O

Select view from the build menu and view the molecules in the wire model.

Record the # of non-bonding pairs of electrons present in each compound.

Select measure angle from the geometry menu and record the bond angles between the central atom and hydrogen for each molecule.

Prepare a printout of the three molecules with their bond angles and non-bonding electrons. Save your work on a disk.

                        Match each compound with the tetrahedral, pyramidal and V shapes.

Look at the Periodic table and make a prediction of the shapes and bond angles for SiH4 and PH3 and H2S.

Conclusion:   How is the chemical reactivity of the hydrocarbons affected by single, double and triple covalent bonds?

                        How is the shape of a molecule affected by the presence of non-bonding electron pairs?

Write a short paragraph to describe how chemical bonds affect the properties of covalent compounds.

[Teaching Standard B- Orchestrate scientific discourse]

Homework:    Read the sections of substitution and addition organic reactions in the textbook.

                        Write the formula and name of the product of the reaction with chlorine and each of the hydrocarbons -butene, methane and ethyne. Identify each reaction as either addition or substitution.