Organic Molecules
Purpose: Learn to write structural formulas, identify isomers, and the effect of multiple
bonds on shape.
Using an organic molecule kit, you will make models of these compounds.
A.
B.
C.
D.
CH4
CH4O
C2H6
C3H8
Write the structural formula for each model A through D on your notebook paper.
A)
B)
C)
D)
Before you take apart model D, try to twist it around the single bond between carbon atoms.
Q1. You can write an "ordinary" formula for a molecule using letters and numbers, as in the case of CH4,
for example. Or you can write a structural formula. Which formula tells you more about the structure of the
molecule? Explain your answer.
Some organic molecules have double bonds between the carbon atoms or between the carbon and oxygen
molecules. Some organic molecules have triple bonds between the carbon atoms within the molecule.
You will need to make use of springs found in the molecular model kit. In the case of a double bond use
two springs and for a triple bond use three springs between atoms.
Procedure:
Make models of these compounds:
A.
B.
C.
D.
E.
C2H2
C2H4
C3H6
C4H8
CH2O
Gently try to twist one of the models in the region of a double or triple bond. Do not break the springs or
overstretch them. Keep models A and B and take apart the others.
Q2. Do models with double and triple bonds between carbon atoms twist as easily those with only single
bonds?
Molecular Shape
1. Make a model of ethane (C2H6).
Q3. Do all the atoms of the molecular model rest on the table? Describe the molecules' shape.
5. Make a model of propane (C3H8).
Q4. Are the three carbons in the propane model in a straight line? Draw a picture of the positions of the
three carbons (ignore the hydrogens in this drawing).
6. Use your model of ethene (C2H4), you will have to use springs.
Q5. The angle between the two single bonds on a carbon atom is different from the angle between a single
bond and a double bond. What is this angle between a single and double bond? What effect has the double
bond had on the shape of the molecule in the region of the double bond?
7. Use the your model of acetylene (C2H2).
Q6. What effect does the triple bond have on the shape of the molecule in the region of the triple bond?
Question 7: You can represent a propane molecule as an "ordinary" formula, as a structural formula, or as
a three dimensional model. What kind of information can you get from each model?
Isomers
If every person in your class made a model of propane (C3H8), the molecule would essentially be the same.
If everyone in your class made a model of C2H6O, there may be two distinctly different models-both of
which are possible.
One model is ethanol, a common alcohol molecule and the other is an ether molecule. These molecules
have the same molecular formula, C2H6O, but different structural formulas. How the atoms are arranged
within the molecule is important. Ethanol and dimethylether have very different chemical and physical
properties and are truly different substances. Isomers have the same molecular "ordinary" formula, but
different structural formulas.
Procedure:
1. Make a model of a butane molecule (C4H10). Write the structural formula of the molecule you have
made on your paper.
2. Try to change the arrangement of the carbon atoms (and the subsequent hydrogen arrangement) to see if
you can make an isomer. (Hint: An isomer for a saturated hydrocarbon is often formed if you can change
the length of the continuous carbon chain.)
Write the structural formula(s) for butane and its isomer(s).
Q8. How many isomers of butane did you make?
3. Make as many unique structural formulas of pentane (C5H12) as you can. Write the structural formulas
of each on your paper.
Q9. How many structural formulas are there for C5H12?
4. Make as many unique structural formulas for hexane (C6H14 ) as you can. Write the structural
formulas of each on your paper.
Q10. How many unique structural formulas are there for C6H14?
Q11. What happens to the number of isomers as the number of carbon atoms increases?
5. Butyne (C4H6) has one triple bond. Make as many structural formulas as you can for this molecular
formula. Write the structural formulas of C4H6 on your paper.
Q12. How were your butyne isomers different from each other?