Many extended structures can be viewed as close-packed layers of large anions, with the smaller cations fitting in between the anions. Larger holes between close-packed anions can hold cations with octahedral coordination. Smaller holes between close-packed anions can hold cations with tetrahedral coordination. The online jsmol resources show these layers and their holes.

The goal of this activity is to have students calculate the empirical formula of a compound given the contents of a unit cell. 

A repeating building block, or unit cell, is used to represent extended structures since shifting a unit cell along its edges by the length of the edge will exactly replicate the extended structure.

We do not cover extended solids (solid state materials) in our general chemistry program. With the exception of students who have taken a course in materials science, Inorganic Chemistry I is the first time our students have encountered solid state structure. Although they have built some visualization skills by working with molecules and symmetry, they do not have robust 3D visualization abilities and have trouble using the language of solid state chemistry (unit cells, packing, filling holes, coordination number, etc…) in the context of structure.

This is a short worksheet that guides students through simple metal lattices (SCP, CCP, HCP) and how filling holes in these lattices results in ionic lattices (NaCl, CsCl, fluorite, etc.).

The worksheet was used as an in-class activity after students had read about the material in the text. This activity is probably suitable for first-year students, though I used it with juniors/seniors.