Low Cost Molecular Models With Laser Cutting

Molecular models are an important tool in chemistry education. I think they are specially useful when you have enough pieces that all students have the opportunity to play with them and build their own models.

Conventional models are expensive, so you may think twice before placing them in the hands of students, specially small children. The solution is to make a low-cost model so everybody can play and you don´t care as much if you lose a piece or ten.

3D printing is not the best way to go for this, since it takes a long time to make a lot of pieces, even small ones. Enter the laser cutter. Fast, easy to use and you can make hundreds of pieces with one 3 mm 60 x 90 cm MDF board. Most people don´t have a laser cutter (I don´t), but I think that this project is worth a trip to a nearby makerspace.

I have used this kind of model in outreach activities and both kids and grown ups love to build the molecules (or to create their own).

Supplies

You will need:

- 3 mm MDF board (check with the people at the makerspace to see what is the area of the cutter and bring the boards cut to size, it will save you a lot of time)

- black, white, red and blue spray paint cans

- 5 mm plastic straws with a bend (if you use a different size, you have to change the drawings)

For the fullerene model I used a 1 mm non-corrugated cardboard sheet, since it needs to be foldable.

Step 1: The 2D Vector Files

If you are a chemistry teacher (I am) and your school has a makerspace with a laser cutter (not my case, but working on it), you may want to have your students make the files for cutting the models. It is an interesting design process. You just want the files ready for use, jump to the end of this step.

The laser cutter machine uses a vector file to guide the laser and cut the material. You can use a free software for this, like Inkscape, or something like AdobeIllustrator or Corel Draw.

To make a 120 degree connector, I started with a rectangle with the width of the straw I wanted to use. I added a circle to the edge and joined them together. I made two copies and rotated them 120 and 240 degrees. A circle can help to align the three pieces. Join them and the connector is ready.

The tetrahedral connector is a little more complicated. You start with the same rounded rectangle and rotate a copy 109 degrees. You need to join them with a circle and then cut a slit that is the size of the MDF board thickness (I used a 3 mm board). If you use a different material, you have to adjust it here.

You can get the files at Thingiverse here: https://www.thingiverse.com/thing:4045445

Step 2: Before Cutting

To make a model of a molecule, you need to identify the atoms. The best way to do this is to use different colors for different atoms. The standard goes like this:

Carbon - black

Oxygen - red

Nitrogen - blue

Hydrogen - white

There are other colors for other atoms (halogens are green, usually), but to make most simple organic molecules, you are ok with these colors.

Painting all the atoms one by one would be a pain, so you need to paint the MDF board BEFORE cutting. I used spray paint since it dries quickly, but you can try with other types. The laser cutter I used had a cutting area of 60 x 90 cm. I divided the MDF board in four parts, covered three parts with newspaper and painted the exposed part, waited for it to dry and painted the others, one at a time. One of these 60 x 90 cm boards will make hundreds of atoms and it is really cheap.

Step 3: Make the Atoms and Connect Your Molecules

Now you have a lot of small pieces with a slit, and you have to glue them together to make the tetrahedral atoms. Just a little drop of glue will work.

I cut the straws to make two sides of "bonds": the smaller one for carbon - hydrogen bonds and the larger for carbon - carbon, carbon - oxygen and carbon - nitrogen bonds. I am not worried with the exact proportions of the bonds, since I use these as a rough idea of the molecule´s geometry.

You can make small molecules like the ethanol "dog" or an aspirin.

What about double or triple bonds? Glad you asked. You can use the bend on the straw to make double bonds. Just cut the straw so it has the same lenght on both sides of the bend and insert two straws in between the atoms.

Step 4: Going Big With Small Molecules

If you want to make a big impression with the models, you may try to make the fullerene and carbon nanotube models. For these models I used a longer straw and the model becomes big enough to fit a child inside it! That´s molecular inclusion for you. A cheap Halloween costume, perhaps?

For these models I used a cardboard sheet and made the 120 degree connectors. I have no idea how it is called in English, in Brazil it is called papel Paraná.The one I used is around 1 mm thick. The best thing about this material is that, unlike the MDF board, it bends. That is necessary for the fullerene model to work. After some uses, tha paper may break, but it is so cheap that you can have hundreds of pieces for a very small price.

Getting the fullerene model together is a challenge. You start with a pentagon, placed hexagons around it, then follow the edges of the original pentagon and place more pentagons in each of them. You may want to have a picture of the molecule handy during assembly.

Carbon nanotubes use the same connector and the same straws, but they have only hexagons. You can make different sizes of it (both in lenght and width). If you make at least 10 hexagons side by side you will be able to make a tube without bending the straws too much.

Step 5: Build Those Models!

The way we present this to the public in our outreach events is like this: we selected several "famous molecules" like aspirin, caffeine, adrenaline, etc. and we made laminated sheets with the structural formula of the molecule and some curiosities about it. The color scheme of the atoms is in the sheet as well. The challenge is for them to make the model following the "map" - looking at the formula and connecting the atoms.

Step 6: Getting Fancy With Your Models

You can make special connectors to make other models.

A hydrogen atom with two connections can be used to show the hydrogen bonds in water and make an ice model. I used a transparent straw in the hydrogen bonds.

Make an octahedral connector and show a cubic lattice like the one in sodium chloride (NaCl).

Upgrade your 120 degree connectors and make a graphite model. Transparent straws can be used to separate the planes.

If you tried my molecular model system and made something with it, tell me in the comments! Send pictures!

If you speak portuguese, you can follow my blog, XCiência: http://www.xciencia.org/.