Chem 122 Laboratory, Spring 1996      Name________________________________

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Molecular Modeling with "ball-and-stick" model kits

For this experiment you will work in pairs. Pick a partner and unpack your model kit.

1. Why do you think the different types of atoms are given different colors? Are these colors the real colors of these atoms, or just arbitrary colors?

2. Locate on the periodic table in your textbook all the atom types included in the kit.

3. How many holes (for bonds) are there in these atoms?

                H            hydrogen               _____
                C            carbon                 _____
                O            oxygen                 _____
                Cl           chlorine               _____
                Br           bromine                _____
4. Construct models for the diatomic molecules hydrogen (H2), chlorine (Cl2), and hydrogen chloride (HCl). What does the bond between the two atoms represent; that is, what is the bond actually composed of?

5. What is the "octet rule" and how does it explain the tendency of oxygen to form two bonds, whereas chlorine, for example, forms only one bond?

6. Construct models for methane (CH4) and for chloroform (CHCl3). What shape is formed by the vertices of the molecule?

7. Construct models for ethane (C2H6), and propane (C3H8). Is there any other way to construct these molecules?

8. Construct a model for butane (C4H10). There is more than one way to construct a molecule with the formula C4H10. How many can you find? Sketch their structures.

9. Ethanol and methyl ether both have the empirical formula C2H6O but different structures. Ethanol is an alcohol and has an -OH group. Ether has a -O- linkage. Construct both molecules and draw their structures here:

10. Some molecules contain so-called "double bonds". In the modeling kit, the curved bonds are used used allow double bonds between atoms. Build models for diatomic oxygen and for carbon dioxide. How many double bonds do these molecules have?

11. Octane (found in gasoline) has 8 carbons and is one of the family of hydrocarbons such as methane, ethane, butane, and propane. What formula would you predict for octane? Can you some up with a general expression that should work for all hydrocarbons of this type? E.g. CnHm, given n, what is m?

12. Chains and rings.

Many organic molecules have chains of carbon atoms. It is also common for atoms to form closed rings. Most drugs, for example, contain rings or 5 or 6 atoms.

Using your molecular model kit, construct a hydrocarbon with the formula C6H12, consisting of a ring of six CH2 groups. This is called cyclohexane. Then construct another hydrocarbon with the formula C6H6, consisting of a ring of six CH groups with alternating single and double bonds between the carbons. This is called benzene, and it is by far the most common ring structure, found over and over again in many different naturally occurring organic compounds. The short-hand line-segment representations of these two structures are:

cyclohexane benzene

13. Chiral (left- and right-handed) molecules.

Maryland Collaborative for Teacher Preparation