Learn how to make a low cost molecular model set, using a laser cutter and plastic straws.
A set of pieces for building models of molecules. The pieces can be made using cardboard or MDF and they are connected using plastic straws.
There are many variations on molecular models available. You can buy molecular model sets, but their cost is high, specially here in Brazil. If the model is expensive, teachers think twice before letting the students freely manipulate the models. Many "alternative" models have been proposed, using many different materials. The model presented here has the possibility of making a large number of pieces at a low cost and very fast. And the work is relatively low, since the machine will do most of it. The only limitation is the access to a laser cutter, but this can be arranged if your city has a makerspace.
HOW TO USE
Molecular models can be used in many ways, in several aspects related to bondig and organic chemistry.
To make the model first we need to identify the the atoms of different elements. We use a color code for that. The carbon atoms are black, oxygen atoms are red and nitrogen ones are blue. These atoms use tetrahedral pieces, that can have 4 connections. Hydrogen atoms are white and have only one connection.
To join the atoms, we use plastic straws. We chose 6 mm straws that have an accordion style bend. We cut the straws in two sizes, one for C-C bonds (or C-O, or C-N) with 5 cm, and another for bonds to hydrogen (C-H, O-H or N-H), with 3,5 cm.
We have used the model in outreach activities where visitors can build models of "famous" molecules. Examples of famous molecules include caffeine, aspirin or adrenaline. We present them with a printed and laminated sheet with both the molecular and structural formulas, and they have to follow the "map" to complete the molecule. Some small kids take a more creative route and play with the set for a long time, like a LEGO set.
We can also build a fullerene model (C60), using cardboard pieces. These pieces have 3 connections at 120 degrees of each other. We use cardboard because we can bend the pieces to make the right angle for the 3D solid.
The same kind of piece can be used to build carbon nanotubes. We use longer straws for these models, and they become big enough that kids can get inside them.
MAKE YOUR OWN
Download the files for the laser cutting at Thingiverse.
You will need:
- MDF board with 3 mm thickness, Size of the board will depend on the laser machine cutting area.
- Paint in red, black, white and blue colors. We used spray paint since it dries quickly.
- 6 mm plastic straws
- White glue
We created the drawings for the laser cutter with a vector illustration software. An example of free software for that is Inkspace. We start with a rectangle with the same width of the straw we intend to use. We join a circle to one of the edges. The shapes are combined so we have only the contour around. To make the fullerene piece, we make three copies and rotate them so they are 120 degress of each other. Then we used a circle to help us align the shapes and combined it all in one contour. This final drawing is ready for cutting. We just need to copy and paste it several times ao we can make as many pieces as we can fit on the board.
To assemble the tetrahedral pieces seems a little more complicated at first. We need to make a 3D object and we want to use the laser cutter which is a 2D tool. We will se that making it on the laser cutter is much faster and cheaper than in a 3D printer. We start again with a rectangle with the same width as before and we round one of the edges. We rotate two copies of this shape around 109 degrees. We join these two pieces and we cut a square thar has the same width as the board thickness.
We paint both sides of the MDF boardwith the color of the atoms we want to make. Adjust the parameters on the machine to cut 3mm MDF. You can make a test using another piece of MDF and adjust the speed and potency of the laser. Finally, don't forget to focus the laser before cutting.
We place several copies of the shape side by side to make a large number of pieces. Each two of the pieces will become an atom. Put a small drop of white glue on the groove and join the pieces to make a tetrahedron.
Your model is ready! We made a box with several divisions for each atom and bonds.