Calcium Fluorite Crystal Structure

[@ripliner3964]

my exam for this is in like... 6 hours so this question certainly wont be answered before then. However what seperates the fluorite structure from a zinkblende structure? I went to the other video you linked in the other comments and it looks as if the fluorite structure is just the zincblende structure expanded into a 3x3 grid of the mini cubes you make and then that forms the fluorite structure. I will attempt to ask my professor before the exam about this but this is the question thats got me the most confused .

[@ScottRamsay]

Calcium fluorite has much larger cations relative to the anions versus zincblende. In calcium fluorite, cations are in simple cubic sites (coordination number = 8) while in zincblende the cations are in tetrahedral sites (coordination number = 4). Also, the stoichiometry is 2:1 anions:cations for calcium fluorite and 1:1 for zincblende.

[@ripliner3964]

@@ScottRamsay you’re crazy for responding so fast, thanks man

[@adams2735]

Calcium in FCC structure and Fluoride ions should be found in 4 tetrahedral interstices/ The stoichiometry shows for every 4 Ca^2+ ions (because (8X1/8) + (6X1/2) = 4)there are 8 F^- ions (8X1=8) . I think you have shown the structure of zincblende

[@Voiceinhead]

no, ZnS has each element having a coordination number 4 and Zn elements are in tetrahedral positions ... he has shown the structure of Calcium Fluorite

[@rajneeshrai1781]

There are 8 tetrahedral voids 2 at each of the body diagonal

[@ScottRamsay]

This structure can be represented either way, the way: a simple cubic lattice of anions with half of the simple cubic interstitial sites occupied OR as an FCC lattice of cations with anions occupying the tetrahedral interstitial sites. It's quite challenging to see that these two are, in fact, the same so I created a video showing how we can move from one to the other, confirming that they are the same. Check it out if you have a chance. (kzbin.info/www/bejne/d4vCpXt4fqeEjbc).

[@meryemayatti5636]

thanks a lot it really helped me

[@kgt94]

Awesome, thanks

[@SATISHKUMAR-zh5il]

This is wrong....CaF2 has FCC lattice not simple cubic

[@suddenlysummerr]

allah razı olsun senden satish kumar god bless you friend

[@ScottRamsay]

Actually, my explanation is correct but it can also be represented as an FCC lattice of cations with anions occupying the tetrahedral interstitial sites. It's very useful for students to learn both approaches to visualizing this structure so I created a video showing calcium fluorite using both approaches (kzbin.info/www/bejne/d4vCpXt4fqeEjbc). Hope you find it helpful.

[@sanskarsoven3762]

U should be ashamed for being from such a great university and giving wrong information.

[@ScottRamsay]

This can be a challenging crystal structure to picture so I can understand your frustration. My depiction is correct, but I'm guessing that you are more familiar with this structure represented as an FCC lattice of cations with anions occupying the tetrahedral interstitial sites. I demonstrate how to visualize calcium fluorite using both approaches in another video (kzbin.info/www/bejne/d4vCpXt4fqeEjbc) I hope this is helpful to you. I always welcome feedback. Good luck with your studies.