Glencoe Chapter 22 Organic Chemistry
Isomerism Lab

Introduction: Two or more substances that have the same molecular formula but different structures and properties are called isomers.  Two main types of isomers exist.  Structural isomers are one in which the atoms are bonded in different orders.  In sterioisomers, all the bonds in the molecules are the same, but the spatial arrangements are different.

To study molecules and isomers, chemists find the use of models helpful.  Colored wooden (or plastic) balls are used to represent atoms.  These balls have holes drilled in them according to the number of covalent bonds they will form.  The holes are bored at angles that approximate the accepted bond angles.

Sticks and springs are used to represent bonds.  Short sticks are typically uses to connect carbon atoms with hydrogen atoms, while longer sticks are used to represent carbon-carbon single bonds.  While single bonds are shown with sticks, double and triple bonds are shown with two or three springs, respectively.

While the sizes of the atoms are not proportionally correct, the models are useful to represent the arrangement of the atoms according to their bond angles.  The models also demonstrate structural isomerism and stereoisomerism.

 

Objective: In this lab, you will work with models of molecules from the alkane family that have 1, 2, 3, 4, 5 carbon atoms.  Molecules in the alkane family are said to be saturated, which means they have only single covalent bonds between the carbon atoms. 

  1. You will compare and contrast the shapes of several organic molecules. 
  2. You will draw molecular structures for several organic compounds. 
  3. You will make models that show the same number of atoms which can be arranged differently. 
  4. You will make two stereoisomers and draw them.
     

Materials:

  • Wooden molecule kit
  • Ruler
  • Protractor
  • Unlined paper (5 sheets)
Prelab Questions - Complete these first before going on to the next part of this lab!

1. Complete this chart:

Name of alkane Formula (CnHn) # of isomers
Methane    
Ethane    
Propane    
Butane    
Pentane    

2. Define COVALENT BOND: ____________________________________________________________________________

3. How many covalent bonds will CARBON form in a compound? __________

4. How many covalent bonds will HYDROGEN form in a compound? _________

5. How many degrees in a tetrahedral angle?  __________o

 

Procedure:

PART I

1. Each hole that has been bored into the ball represent the potential for a single chemical bond.  Count the number of holes present in the different colored balls.  Record your answers onto the data table.

2. On the data table, complete the OUTER SHELL ELECTRON CONFIGURATION for each colored ball. 

3. On the data table, complete the identity (name) for each colored ball.  (The colors of bromine chlorine, iodine have already been recorded for you.)

4. On the data table, determine the number of UNPAIRED electrons for each atom.

 
Ball color Number of holes Name of atom Outer shell electron configuration # of unpaired electrons
Red

 

        
Orange

 

   bromine    
Yellow

 

        
Green

 

   chlorine    
Blue

 

        
Purple

 

   iodine    
Black

 

        

PART II

1. Using the molecule kit, make METHANE.  Here is the structural formula for methane:

      H
       |
H - C - H
       |
      H
Compare what you made to the structural formula above.  How, specifically, are they different?

_________________________________________________________________________________________________________________

2. Using the molecule kit, make BROMOMETHANE.  What are the structural differences between methane and bromomethane?

_________________________________________________________________________________________________________________

3. Using the protractor, measure the angle between two of the hydrogen atoms and carbon.  How many degrees? _____________

 

 

4. Using the molecule kit, make a molecule of ETHANE.  Draw the structural formula in the left box and then, accurately draw the molecule as you see it in 3D.
 

 

 

 

 

  

5. Does ethane have any isomers? ___________  If yes, how many? __________

6. Using the molecule kit, make a molecule of PROPANE. Draw the structural formula in the left box and then, accurately draw the molecule as you see it in 3D.
 

 

 

 

 

  

7. Does propane have any isomers? ___________  If yes, how many? __________

 

8. Using the molecule kit, make a molecule of BUTANE. Draw the structural formula in the left box and then, accurately draw the molecule as you see it in 3D.
 

 

 

 

 

  

9. Does BUTANE have any isomers? ___________  If yes, how many? __________  Draw them here:

 

 

 

 

10. Construct two different models of CHLOROPROPANE.  What would the chemical formula be?  ________________

11. Does CHLOROPROPANE have any isomers? ___________  If yes, how many? __________  Draw them here:

 

 

 

 

 

12. Construct the three different isomers of PENTANE.  Draw them here:

 

 

 

 

 

 

 

 

 

 

 

 

13. Construct a molecule of BENZENE - this is an aromatic hydrocarbon and has 6 carbons.  Draw the structural formula in the left box and then, accurately draw the molecule as you see it in 3D for the CHAIR form and the BOAT form! 
 STRUCTURAL FORMULA

 

 

 

 

 

 BOAT FORM CHAIR FORM

14. Are the two structures you drew in the boxes (chair and boat) isomers?  ________________

If not, what are they? ________________________________________

Analysis:

1. How does the structural diagram of methane compare with the model you made? ____________________________________________________

_________________________________________________________________________________________________________________________

2. What is the difference in the shape of the molecules of methane vs. bromomethane? _________________________________________________

_________________________________________________________________________________________________________________________

3. How did what you measured with the protractor in terms of the tetrahedral angle compare to the accepted value of 109.5o?  Why would there be a difference?

_________________________________________________________________________________________________________________________

4. Gasoline is a mixture of alkanes that generally have between 4 and 12 carbon atoms.  It is a liquid at room temperature.  Paraffin wax is a mixture of hydrocarbons.  Would you expect the number of carbons per typical molecule to be FEWER or GREATER than the number of carbons that make up gasoline?  WHY?

Circle one:         FEWER             GREATER

WHY?__________________________________________________________________________________________________________________________

5. Methane is the primary component of NATURAL GAS (what you use to heat your home from Citizen's Gas) but propane and butane are used as BOTTLED-GAS products (butane in cigarette lighters and propane in tanks you use in your gas grill).  Which gas (natural gas or bottled gas) would you expect to rise in the air and which gas would you expect to settle to the ground.  WHY?

Complete:         ____________________________ RISES       

while ____________________________      SETTLES.

WHY? ________________________________________________________________________________________________________________________

 

 

 

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