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I am confused about the different cubic lattice that are there.
I think its body centered, face centered. How do yo figure out how many atoms in each?

what else should we know about this?
 

alanan84

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Cubic Crystal System (unit cells):
  • simple cubic – atom @ each point of the cube, each is shared by 8 other cells à (1/8)*8 corners = 1 atom per cell
  • body-centered cubic – 1 atom @ center of the cube + an atom @ each point of the cube (shared by 8 other cells) à[ (1/8)*8 corners]+1 body = 2 atoms per cell
  • face-centered cubic – 1 atom embedded @ the center of each cube face (shared with 1 other cell) + an atom @ each point of the cube (shared by 8 other cells) à (1/8) * 8 corners + (1/2) * 6 faces = 4 atoms per cell
 

jefff

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Cubic Crystal System (unit cells):
  • simple cubic – atom @ each point of the cube, each is shared by 8 other cells à (1/8)*8 corners = 1 atom per cell
  • body-centered cubic – 1 atom @ center of the cube + an atom @ each point of the cube (shared by 8 other cells) à[ (1/8)*8 corners]+1 body = 2 atoms per cell
  • face-centered cubic – 1 atom embedded @ the center of each cube face (shared with 1 other cell) + an atom @ each point of the cube (shared by 8 other cells) à (1/8) * 8 corners + (1/2) * 6 faces = 4 atoms per cell
hmm
 
May 15, 2009
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Each corner atom is worth 1/8, each face atom is worth 1/2, and each center atom is worth 1.
For Face center cubic you have 8 corner atoms, and 6 face atoms:
8(1/8) + 6(1/2) = 1+3 = 4 atoms




For Body center cubic you have 8 corner atoms, and 1 center atom:
8(1/8) + 1 = 1+1 = 2 atoms



For simple cubic you have 8 corner atoms:
8(1/8) = 1 atom




 

suhshi

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how would you apply this knowledge to this question:

how many cl ions are in contact with any Na ion if sodium chloride crystallizes in a face centered cubic lattice of chloride ions, with the smaller sodium ions occupying holes between the chrloride ions
 

DaveyK

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I was just about to post something on this same topic lol... strange.

thanks for the overview nze, I've been looking around the web for info on this and that is the best explanation I've seen :)

I do still have a question however... out of acs gchem:

"Copper crystalizes in a face centered lattice. If the edge of the unit cell is 362pm what is the radius of the copper atom?"

the answer is 128pm... I'm assuming there is some ratio to use, but since acs doesn't give explanations and I'm a little lost, if someone could explain how they got this number, I would appreciate it:)
 
May 15, 2009
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I was just about to post something on this same topic lol... strange.

thanks for the overview nze, I've been looking around the web for info on this and that is the best explanation I've seen :)

I do still have a question however... out of acs gchem:

"Copper crystalizes in a face centered lattice. If the edge of the unit cell is 362pm what is the radius of the copper atom?"

the answer is 128pm... I'm assuming there is some ratio to use, but since acs doesn't give explanations and I'm a little lost, if someone could explain how they got this number, I would appreciate it:)
Look at my posts here:
http://forums.studentdoctor.net/showthread.php?t=628255&highlight=radius+of+copper+atom

Hopefully, they will answer your question.
 

DaveyK

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:phah.. should have used the search function. that's perect, thanks!