Initial Publication Date: October 16, 2006


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  1. What is the coordination number for Mg? for Al?
  2. What is the strength of the bonds around each Mg cation? What is the strength around each Al cation? (To do these calculations, divide cationic charge by the number of bonds.)
  3. Consider a single oxygen anion. What cation(s) is it bonded to? Add up the strength of the bonds (you just calculated them). Does the total add up to oxygens anionic charge? Why or why not?
  4. Note the overall cubic form of this structure. Orient the structure so you are looking down the body diagonal (the projection of the three crystallographic axes on your screen should be pointing away from each other at 120° angles). The oxgyen atoms "nearest" you form the top layer of a close-packed array; successive layers are "away" from you within the structure. What type of close packing is this: HCP or CCP?
  5. Notice that the body diagonals of the structure are 3-fold axes. How many 3-fold axes are present?