Question

The number of third nearest neighbours of Na+ ion in NaCl crystal is _____.

Answer 1

Answer:

Consider the Na+ ion sitting at the body centre (tetrahedral void) the nearest neighbor would be the face centres (Cl−) these would be 6 in number. Now comes the next nearest neighbors. These are other Na+ ions sitting at edge centre. These would be 12 in number (12 edges surrounding a body center).

Answer 2

The number is 12.

• The Cl ions in NaCl have an FCC structure, whereas the Na ions are in octahedral gaps. At the moment, these voids may be seen at the edge and body centers.
• When the Na is seated in the body center, the facial centers are the closest neighbors. There would be a total of six of them.
• The closest neighbours are now other Na ions at center of the edge There would be a total of 12 of them. As a result, the next closest neighbors of Na ions are 12 times greater than Na ions.