Reusing Waste Plastic Caps to Build Inexpensive and Easily Changeable Crystal Structure Models

An activity of using waste plastic caps and wooden sticks (or steel wires) to construct crystal structures is described. Caps with different colors represent different atoms/ions/interstices, and sticks are employed to carry the caps and describe the positions of atoms/ions/interstices. The cap-and-stick model clearly demonstrates crystal structure characteristics from multiple viewpoints. Students have participated in this activity, and their feedback suggests that the activity is helpful in deepening their comprehensions of lattice structures, unit cells, packing arrangements, distribution and filling of vacancies, and coordinates of atoms/ions/interstices and cultivating hands-on ability and a spirit of teamwork.