This paper describes the synthesis of a stable compound of sodium and helium at very high pressures. The paper uses computational methods to predict likely compounds with helium, then describe a synthetic protocol to make the thermodynamically favored Na2He compound. The compound has a fluorite structure and is an electride with the delocalization of 2e- into the structure.
This paper would be appropriate after discussion of solid state structures and band theory.
The questions are divided into categories and have a wide range of levels.
Dong, X.; Oganov, A. R.; Goncharov, A. F.; Stavrou, E.; Lobanov, S.; Saleh, G.; Qian, G.-R.; Zhu, Q.; Gatti, C.; Deringer, V. L.; et al. A stable compound of helium and sodium at high pressure. Nature Chemistry 2017, 9 (5), 440–445 DOI: 10.1038/nchem.2716.
After reading and discussing this paper, students will be able to
- Describe the solid state structure of a novel compound using their knowledge of unit cells and ionic crystals
- Apply band theory to a specific material
- Describe how XRD is used to determine solid state structure
- Describe the bonding in an electride structure
- Apply periodic trends to compare/explain reactivity
The questions are divided into categories (comprehensive questions, atomic and molecular properties, solid state structure, electronic structure and other topics) that may or may not be appropriate for your class. To cover all of the questions, you will probably need at least two class periods. Adapt the assignment as you see fit.
CrystalMaker software can be used to visualize the compound. ICE model kits can also be used to build the compound using the template for a Heusler alloy.
Students could be evaluated based on their participation in the in-class discussion or on their submitted written answers to assigned questions.
This LO has not been used in a class at this point. Evaluation results will be uploaded as it is used (by Spring 2018 at the latest).