Problem 82
Page 475
Section: Cumulative Problems
Chapter 11: Liquids, Solids, and Intermolecular Forces
Given information
Copper iodide crystallizes in the zinc blende structure. The separation between nearest neighbor cations and anions is approximately 
, and the melting point is 
. Potassium chloride, by contrast, crystallizes in the rock salt structure.Even though the separation between nearest neighbor cations and anions in potassium chloride is greater (
), the melting point is still higher (
). Explain why the melting point of potassium chloride is higher than that of copper iodide.
Step-by-step explanation
Copper iodide crystallizes in the zinc blende structure.Where 
ions are the cations and 
ions are the anions.
The ions are anions and are face centred.Hence the coordination number is 
.Each anion is surrounded by four cations and the same for cations also.
The coordination number of the cubic cell is 6.Hence one anion is surrounded by or bond to 
cations and vice versa.
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