I have tried to adapt this laboratory from actual three-dimensional models you could hold in your hands to computer models freely available on the internet. Some things are lost in the process, such as the space-filling aspect, which is really necessary to appreciate the importance of closest-packed layers. Nevertheless, I hope you can get some sense of the three-dimensional structures by looking at the computer models. Even if you can find a quick answer to some of the questions, make sure you really rotate the models and look at them from all angles to convince yourself that you understand the answers in three dimensions!
1. Look at the NaCl structure here: https://www.chemtube3d.com/_rocksaltfinal/.
a. What is the coordination number of each of the green atoms, i.e. how many purple
atoms are nearest neighbors to a green atom? What is the coordination number of each of the purple atoms? Do not consider the atoms at the edge or face of the cube but focus on the atoms on the interior of the model.
b. Rotate the model until you can clearly see a C4 axis perpendicular to your screen. What other symmetry elements are evident from this perspective?
c. Now rotate the model until you can see a C3 axis. What other symmetry elements are evident from this perspective?

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