This laboratory activity gives students an opportunity to view the basic structural forms of most metals. Students learn the meaning of coordination number, crystal lattice, and packing. Later, students will be able to correlate properties with structure.
Two common ionic crystal lattices,-rock salt and wurtzite-and their coordination numbers, give students some insight into why ionic solids are brittle with relatively high melting points, and why different-sized ions form different types of crystal lattices. Each ion is surrounded by oppositely-charged ions, producing strong attractions, holding the ions in place.
This activity is appropriate for all levels of students. Basic students probably should not complete the extensions.
Students with no previous knowledge of crystals can perform the activity. There are no prerequisite concepts other than those listed for this topic. The activity could also be used to support the topic of condensed states of matter.
Students should be able to complete the activity in one 50-min. period.
No special precautions are necessary. If students work in the chemistry laboratory, they should wear protective goggles since there may be hazardous materials nearby. Advise students to follow regular laboratory safety procedures.
Have sufficient spheres available and placed either in boxes for each two-student group or readily obtainable by students. Consider preparing a set of layers for the models glued together to show students what the layers should look like.
Minimal pre-lab discussion is required. If glued-together layers are available, they could be shown to students. Directions for connecting spheres should be given and also demonstrated.
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