Coordination number for fcc and NaCl

[Prashasti]

Why is the coordination number for fcc 12, but that in NaCl 6? NaCl crystallises in ccp (or fcc) lattice, then how is it possible?

 

[Greg Bernhardt]

I'm sorry you are not generating any responses at the moment. Is there any additional information you can share with us? Any new findings?

 

[DrDu]

You have to differentiate between the lattice and the crystal structure. Some metals crystallize in a fcc lattice with a primitive basis, i.e. there is only one atom in the primitive cell. Then you can show that each of this metal atoms is coordinated by 12 other atoms. In NaCl, there are two atoms per primitive cell and this changes the situation. It is still true that e.g. each Na has 12 nearest Na ions in that lattice.