Building Molecular Models of Simple Covalent Molecules

Day Two

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

Special Note: I will deduct 10% off your grade for playing with the model sets; as in "Look Mr. 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) Chloro-substituted alkanes are alkanes which have had one or more of their hydrogens replaced by chlorine atoms. Build the following models:
1. monochloromethane, CH3Cl A picture of monochloromethane
2. dichloromethane, CH2Cl2 A picture of dichloromethane
3. monochloroethane, C2H5Cl A picture of monochloroethane
4. dichloroethane, C2H4Cl2 A picture of dichloroethane

Please note that there are two structures in the last picture, which differ in the placement of their chlorines. Both have the same formula, C2H4Cl2, but they have different connectivities. They are structural isomers of one another. In your data table, draw both. One is named 1, 1-dichloroethane and the other is 1, 2-dichloroethane. What do the numbers refer to?

b) Chloro-substituted alkenes are alkenes which have had one or more of their hydrogens replaced by chlorine atoms. Build the following models:

5. monochloroethene, C2H3Cl A picture of monochloroethene
6. dichloroethene, C2H2Cl2 A picture of 1, 1-dichloroethene

Please note that your structure may be different than the one in the picture. The name of the compound in the picture is 1, 1-dichloroethene. Rearrange your model and draw the structural formula in your data table.

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 seven structures to be drawn for this section of the lab.


Cis-trans Isomerism

Cis-trans isomers are two substances which have the exact same connectivity. They are two different structures because of inhibited rotation around the double bond.

Example #1: cis-1, 2-dichloroethene and trans-1, 2-dichloroethene. In the cis structure, the two chlorines are on the same side of the doule bond. In the trans structure, the chlorines are on opposite sides of the double bond. The reference plane for "same" and "opposite" is through the two carbons and double bond, such that one single bond from each carbon projects above the plane and one projects below.

Make both structures and then, WITHOUT pulling the model apart, try and bend or twist one into the other. You can't!! And that's the point. There are two different structures. Draw the two structures and identify each with its name

A picture of both cis and trans structures together.

Example #2: cis-2-butene and trans-2-butene. The but- prefix indicates that there are four carbons, the 2 indicates the placement of the double bond. Cis and trans then refer to the orientation of the first and fourth carbons. There are NO branched carbons in this molecule, the four carbons are in a chain.

Using the model building kit, make both the cis and trans structures for 2-butene, then draw (and name) the structures on paper.

Go to the Day Three Instructions for this lab.