Building Molecular Models of Simple Covalent Molecules

Day Four

Before asking your teacher questions about how to do the lab, please read carefully, twice, the entire "Day Four" document.

Special Note: I will deduct 10% off your grade for playing with the model sets; as in "Look ChemTeam, at this weird structure I made" or if I see you making a structure not in the assignment. On the second occurrence, I will zero your grade.


1) Using a model building kit, construct models of a variety of simple covalent molecules.
2) Draw Lewis structures and/or structural formulas of selected models.
3) Draw all the isomers of selected formulas.

Brief Overview

In 1874, J. H. van 't Hoff (1901 Nobel Prize in Chemistry) was the first to suggest that molecules have a three-dimensional structure. He used this idea to explain several previously puzzling facts about chemical compounds.

In this lab, we will use a kit to model the 3D structure of a number of molecules, including several that van 't Hoff focused on. After building the molecular models, you will draw them on paper in a manner intended to represent the 3D appearence. You will also draw Lewis structures for some of the molecules as well as isomeric structures for those formulas that have them.


The parts of the kits are not toys. Use them only as instructed and only for the purposes of the lab.

Equipment List

One molecular model kit


Part I. Preliminary Steps
1) If necessary, refer to Day One for instructions. If not, proceed directly to Part II.
Part II. Experimental Steps

2) Following the list below, continue to build models. There are not enough atoms to build all the molecules discussed below, so build some, then break them down, then build more.

a) Cycloalkanes are compounds which have only carbon and hydrogen with ONLY single bonds. However, there is a twist - the carbons are connected in a circular (it's called a ring) manner. The carbons are NOT in a straight chain, but rather the two "ends" of a straight chain are connected to each other. (Please use the thinner bonds to make the carbon to carbon single bonds in cyclopropane.) Build the following models:
1. cyclopropane, C3H6 A picture of cyclopropane
2. cyclobutane, C4H8 A picture of cyclobutane
3. cyclopentane, C5H10 A picture of cyclopentane
4. cyclohexane, C6H12 A picture of cyclohexane

b) Cycloalkenes are compounds which have only carbon and hydrogen with ONLY one double bond and the rest single bonds. Remember, cyclo- means that the carbons are connected in a ring manner. Do NOT draw the carbons in a straight chain. (Please use the thinner bonds to make the carbon to carbon single bonds in cyclopropene.) Build the following models:

5. cyclopropene, C3H4 A picture of cyclopropene
6. cyclobutene, C4H6 A picture of cyclobutene
7. cyclopentene, C5H8 A picture of cyclopentene
8. cyclohexene, C6H10 A picture of cyclohexene
Part III. Clean-up Steps
3) Unconnect all bonds from the atom models and replace in the box. Inspect around your table top and on the floor for lost atoms or bonds.

Data Table

Do a data table in the style of the Day One instructions. There are 8 structural formulas and 2 Lewis structures to be drawn.


1) Benzene is an important substance and has the formula C6H6. It is a ring structure and the ring has alternating single and double bonds. To the right is a picture of one possible structure. Draw it and the other possible structure of alternating single and double bonds. (These two structures are resonance structures of each other.) In honor of the person who first proposed the 'ring' bonding arrangement, they are also called the Kekule structures.

There are some alternate structures for benzene called the "Dewar structures," named for James Dewar, a pioneer in low-temperature research and, in 1898, was the first man to liquefy (and later solidify) hydrogen. Find and draw the Dewar structures for benzene.

2) Build this molecule: CHClBrI. The four atoms attached to the carbon should be different colors. There are two ways to build this model and the two structures are mirror images of each other. Draw the two isomers using three-D structural formulas (you need not draw Lewis structures). They are called "optical isomers" because of a certain behavior when a solution of pure isomer (not a mixture of the two) is exposed to a certain type of light.

You need to find out what type of light is involved and what happens to the light. What does EACH pure isomer do to the light? What does a 50/50 mixture of the two isomers do to the light? A 50/50 mixture of the two isomers is called a "racemic mixture."

3) Research cubane (C8H8) on the Internet. In a short paragraph, discuss possible uses for cubane. By the way, cubane was only synthesized in 1964 and interest in possile uese has only arisen in the past 10 years or so. Also, locate and print out (not full page, you can make it small) a "ball and stick" model of cubane. Your paragraph should be handwritten (not typed), consequently, you may tape your printout to the page you hand in.