Building Models of Isomers

organic model kit

I have been looking at model building labs in some of my previous posts and would like to continue with that theme. In my last post I talked about an activity where students try to recognize functional groups by examining previously built molecules. This time I want to focus on an activity where they build multiple models to try and identify isomers.

My basic approach to these activities is always the same. I want students to be building models and have myself walking around from station to station to critique their models and make them keep building until they get it correct. The paper that accompanies this assignment is very easy for me to grade. I rubber stamp each structure once they get it right. They must have all the models of a specific compound in front of them to get the credit for building. This is great because it means that they see both (or more) structures at the same time.

I am sure that this is not a new activity but I have taken it and tailored it to my style of teaching. I love to be able to walk from station to station for the whole period and have multiple interactions with each student. In fact there is no way a student can get through the activity and not have a conversation with me. I have tried several variations of grading this. One is that you can have one paper per two students or one paper per person. I have also considered and once tried a paper for a group of four kids. This speeds things up nicely when it comes to checking papers! Usually I pick a point value for each stamp earned and just count up the number of stamps at the end of the period. On some occasions I have had strong classes where I knew at the end of the period every kid had a perfect score and that allowed me to not collect papers, but to just give everyone present a perfect score.

I think the moral of my story here is to stay away from the canned lessons that you see from publishers. Look at a lesson and tailor it to your needs, your equipment, and your class time. What works for one teacher may not work for another.


isomers, positional isomers, structural isomers

Procedure time: 
50 minutes
Time required: 

one 50 minute class


Enough organic molecule sets for each group to build all of the isomers.The molecular model kits I use are from Carolina: Advanced Level Chemistry Set Article Ref: MMS-002 - 64. 


The first molecules we look at are C2H4Cl2. This is a simple positional isomer but since it is the first one we build, many of my students think simply twisting the molecule makes an isomer. It provides a great opportunity to show that to be an isomer you cannot have two molecules that can be superimposed in any way. Once a student gets this concept the rest of the activity goes much faster.

The second species we talk about is C4H10. I am sure many of you have had students take this straight chain and turn it into a U and a Zig Zag and think that they were different. This molecule shows structural isomers nicely by making the students figure out that butane and 2 methyl propane have the same molecular formula but different structures.

The third scenario is a variation of C4H10. I tell my students to keep those models and use them as the basis for their next answer. The new molecule is C4H9OH. There are four distinct isomers of this alcohol and if the groups of two students work with another group of two they have the ability to show all four at the same time. This is a very challenging set for most students but I am always impressed that some groups get it immediately.

My next scenario is C4H6. There are two isomers possible by moving the triple bond. Students get this one fast. I tell them in advance that it must have a triple bond. One time I didn’t and that made for lots of confusion.

C4H8 is the next molecule. This contains a double bond and brings in the idea of cis trans structures in addition to the movable position of the double bond. This is without a doubt the most difficult isomer for my students to get. It takes a considerable amount of time for them and I love it because it pushes them into really applying themselves.

The last scenario is hexane. I actually do not have students build these, they only have to draw them. I like this for several reasons. One is that if a student is not finished by the end of the period they can do it at home. If they are done with their model building it is a nice and more involved question that produces five isomers and takes some good thought. I do allow students who are finished to walk around the room also to interact with other groups. I am very fond of the discussions I hear come out of activities like this.


Using the assignment page, build the assigned molecules using the molecular model kits. You are told how many isomers of each you need to build. Get them approved and stamped by the instructor. Once you have the correct model, draw a simple diagram of each structure and write name the compound next to it. 


Aquire model kits


I created this activity for use with my students at Francisco Bravo Medical Magnet High School, Los Angeles, California.