I usually grade one student handout per pair and typically have 1 pt per answer on the worksheet, but take the total out of 60 pts (which ends up giving them a couple of free points).
Last semester my 17 students had an average of 47 out of 60 on the lab--a bit lower than usual for that lab. The high was a 57 and the low was a 39. There were lots of different individual errors, but errors in identifying which of the first structures were closest packed and errors in % of holes occupied were common.
This first-year laboratory is designed to give students an introduction to basic solid-state structures using both CrystalMaker files and physical models. I think this would work in a foundations level inorganic course as well. It could be used alternatively as an in-class activity or take-home problem set depending on the instructor. It was adapted by me and later, David Harvey, from an original activity that was posted as an educational resource on the CrystalMaker website in the mid 2000s.
Students will be able to
- articulate how the atoms in a simple cubic, face-centered cubic, and body-centered cubic unit cell are arranged
- determine the coordination number of particular atoms in a unit cell
- count the atoms or ions in a unit cell and determine the empirical formula based on that
- determine the length of a side of a unit cell based on the radius of an atom
- visualize the holes in different kinds of unit cells and see how ionic solids can be built by putting ions in those holes
- describe the forces holding different solids together
- calculate the % of filled and empty space in lattices
- identify closest packed structures
- Computer lab (approximately two students per computer) with CrystalMaker installed (it can be the student version if necessary)
- Physical models from Klinger Educational Products
- simpe cubic
- zinc blende
- Box of pennies
- Mineral samples of calcite, fluorite, and NaCl (if you want to do the bonus)
I usually take one day of class to introduce students to CrystalMaker and all of the basic definitions and ideas of this lab before they start working on the stations. Typically I will work through the first station and then part of NaCl to show them some of the main ideas they will be using, asking them to provide answers (which are typically wrong on the first try!). I am typically circulating around answering questions as the students work through the lab. For a lab section of 24 working in 12 pairs, having one set of physical models seems adequate, but particularly at the beginning of the lab it might be helpful to have two sets of the face-centered cubic and body-centered cubic structures. The 12 computer "stations" are arranged in folders inside a Solid State Lab folder on the desktop of the lab computers, so students can just click on the correct folder and correct files as they work their way through the lab.