Communication pubs.acs.org/jchemeduc
Building Large Molecular Models with Plastic Screw-On Bottle Caps and Sturdy Connectors Dawid Siodłak* Faculty of Chemistry, University of Opole, Oleska 48, 45-052 Opole, Poland S Supporting Information *
ABSTRACT: An improved method of connecting atoms formed with screwon bottle caps is described. Fishing line (artificial polymer), steel wire, and countersunk bolts with nyloc nuts are proposed as sturdy connectors. Advantages and disadvantages of each method are described. The molecular models are stable while handling, can be built in a relatively short time at low cost, and can be useful at every level of education. The method is an alternative to professional model kits, in particular in construction of large models for long-term usage.
KEYWORDS: Molecular Modeling, Molecular Properties/Structure, Stereochemistry, Hands-On Learning/Manipulatives
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INTRODUCTION
Three-dimensional visualization of chemical compounds is crucial in understanding their chemical, physical, and biological properties. Apart from computer modeling, solid molecular models, designed to be held in the hand, still remain excellent didactic tools at every step of education. Application of professional model kits seems to be the first choice; however, there are disadvantages in construction of large models for long-term usage. The large models usually demand many elements of the same type. As a consequence, the use of a few model kits is required, and the cost of a model increases. Very often the remaining elements of the used model kits are of little use. To overcome this problem, a few approaches were published showing how to construct the molecular models using 3D printing,1−4 whiteboard markers,5 ping-pong balls loaded with magnets,6 or marbles and epoxy glue.7 In the previous report8 it was shown that screw-on bottle caps can be used as a promising alternative. With their variety of colors and dimensions, and almost unlimited accessibility as recyclable material, they seem to be very suitable for this purpose. Polyethylene screw-on bottle caps, when stacked together at the edges, can be joined by thermal welding to form model atoms (Figure 1). To create models of molecules, the atoms were joined also by thermal welding using an alcohol burner or by using hot polymer glue. Unfortunately, this junction between the atoms has a tendency to disconnect with increasing weight of the large models while handling. Herein methods are used to overcome this problem. © XXXX American Chemical Society and Division of Chemical Education, Inc.
Figure 1. Constructing a model atom by thermal welding of two polyethylene screw-on bottle caps using a soldering iron.
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MATERIALS Polyethylene screw-on bottle caps are the main building material of the models. Fishing line (artificial polymer), steel wire, and countersunk bolts with nyloc nuts (3 mm diameter) are proposed as sturdy connectors. In addition, the following tools are useful in creating the models: a soldering iron, sandpaper, wire strippers, a pair of pliers, a screwdriver, a utility knife, a marker, two pairs of tweezers, polymer glue sticks, a glue gun, and a drill with a 3.5 mm bit (Figure 2). Received: July 31, 2016 Revised: November 9, 2016
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DOI: 10.1021/acs.jchemed.6b00576 J. Chem. Educ. XXXX, XXX, XXX−XXX
Journal of Chemical Education
Communication
Figure 3. Connection geometry for an atom constructed from a conventional model kit (top row) and the screw-on bottle cap model (middle row). The two most common types of hybridization, sp2 or sp3, can be readily modeled using the screw-on bottle cap approach described here (bottom row).
model. Detailed methods of the model construction, with materials and tools, are presented in Supporting Information.
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HAZARDS Thermal welding creates a small amount of vapor from the melting plastic. Procedure should be carried out using a fume hood (standard kitchen equipment) or well-ventilated place.
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Figure 2. Top: Examples of four different sizes and colors of polyethylene screw-on bottle caps used as material for creating the model atoms. Middle: Three examples of materials for connecting the caps to form compounds: fishing line, steel wire, and nuts and bolts. Bottom: Tools required for making the models described: drill with drill bit, glue gun, polymer glue stick, sandpaper, wire strippers, pliers, screwdriver, utility knife, marker, tweezers, and soldering iron.
RESULTS AND DISCUSSION The present method was checked by construction of relatively large models of carbon allotropes: nanotube, graphene, graphite, fullerene C60, diamond, and a peptide polyalanyl αhelix. Each method has some advantages, as well as drawbacks.
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Fishing Line
This type of connection requires well-tied knots. At least three loops are needed to prevent disconnection. It is good to tightly tie the knots using tweezers. The holes in the bottle caps can be relatively small. Each junction can be separately tied, so that the construction can be created step by step. Also, accidental loosening of a single junction does not influence the stability of the whole model. However, this junction is flexible. Thus, the proper shape and rigidity of the molecular models can be obtained by curing the junctions using hot polymer glue. The method works best when relatively small caps are used (Figure 4).
PROCEDURE To create a selected model, the specified number of polyethylene bottle caps must be collected. Atoms of a given element must be represented by the caps of the same type and color. Each atom is formed by junction of two caps, so that the number of caps must be twice greater than the number of atoms in the model. The bottle caps should be washed with dish soap, and their edges should be aligned with sandpaper. Three materials are proposed as a permanent connection: fishing line (artificial polymer), thin steel wire, and small bolts with nuts. In order to make the connection, small holes must be placed in the sides of bottle caps using an electric soldering iron and/or a drill. To form the main structure or important structural elements, one bottle cap for each modeled atom must be joined to another using the chosen connector. To complete the model, the second bottle cap of each atom must be joined by thermal welding using a soldering iron. Figure 3 presents the geometry of connections, which take into account the two most common types of hybridization, sp2 and sp3. Despite of the cylindrical shape of the caps, the geometry of connections is good enough to present properly the shape of a molecular
Thin Wire
Wire is a rather rigid material; thus, the junctions do not have to be stiffened by using the polymer glue. Also, several caps can be joined at once using a single piece of wire, which makes the construction process relatively fast. This method works best for a diamond model as well as graphite, in which each atom has multiple bonds (Figure 5). However, it is difficult to fix a loosening of a single bond. For example, for the α-helix model, it works well in construction of the main chain together with stabilizing N−H···O hydrogen B
DOI: 10.1021/acs.jchemed.6b00576 J. Chem. Educ. XXXX, XXX, XXX−XXX
Journal of Chemical Education
Communication
Figure 4. Top: Connecting the caps using fishing line. Bottom: Model of a carbon nanotube showing the regular repetition of caps connected with fishing line and glue.
Figure 6. Top: Connecting the caps using bolts with nuts. Bottom: Model of an α-helix of caps connected with nuts and bolts. Colors for elements: dark blue, carbon atoms; light blue, nitrogen atoms; red, oxygen atoms; white, hydrogen atoms in N−H···O internal hydrogen bonds; yellow, α hydrogen atoms of the main chain and β hydrogen atoms of the side chains.
bonds, but the arrangement of the side alanyl chain residues is rather difficult. Bolts with nuts
In the presented models, 3 mm countersunk bolts were used with nyloc nuts to prevent unscrewing. This is the most stable junction. Each junction can be separately and very precisely fixed. The model is rigid and can be created cap after cap, which is very convenient. Drawbacks are the relatively highest cost and possible deformation of the bottle caps if the junctions are screwed too tightly. Also, bigger holes must be made in the bottle caps, using a soldering iron and then expanding the hole using a drill (3.5 mm). This method works best when relatively large caps are used (Figure 6). The presented models were used in an organic chemistry course and as exhibits at an annual regional science festival.
Figure 5. Top: Connecting the caps using steel wire. Bottom: Model of graphite showing the layer structure of caps connected with steel wire.
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DOI: 10.1021/acs.jchemed.6b00576 J. Chem. Educ. XXXX, XXX, XXX−XXX
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ASSOCIATED CONTENT
* Supporting Information S
The Supporting Information is available on the ACS Publications website at DOI: 10.1021/acs.jchemed.6b00576. Detailed instructions regarding how to make the described molecular models as well as other details (PDF)
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Dawid Siodłak: 0000-0002-1686-5215 Notes
The author declares no competing financial interest.
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ACKNOWLEDGMENTS I would like to thank my dear colleagues and students from the Faculty of Chemistry, University of Opole, for their help in gathering the screw-on bottle caps.
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REFERENCES
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DOI: 10.1021/acs.jchemed.6b00576 J. Chem. Educ. XXXX, XXX, XXX−XXX
