Question

Explain nearest neighbour in NaCl

(1st and 2nd and 3rd nearest neighbours)

Personal doubt- I am not able to upload image it says url missing

Answer 1

Sodium chloride has a face centred cubic (fcc) structure. Na+ ions occupy the corners and face centres of a cube. The Cl – ions are present at the body and edge centres.One unit cell of sodium chlorideconsists of 14 Na+ ions and 13 Cl- ions or vice versa. These ions correspond to 4 units of Na+Cl-, i.e., one unit cell of sodium chloride contains four Na+Cl- units ( 4 Na+ and 4 Cl- ions), per unit cell.

In sodium chloride structure , each Na+ ion has the following neighbours:

1. Six Cl- at a distance of r, where r is the distance between Na+ and Cl-.
2. Twelve Na+ at a distance of √2 r (as the next nearest neighbour)
3. Eight Cl- at a distance of √3 r 9as the third nearest neighbour)
4. Six Na+ at a distance of √4 r or 2r (as the fourth nearest neighbour).

AgCl, AgBr, Kcl, RbCl and the oxides and sulphides of alkaline earth metals (expect beryllium sulphide ) have sodium chloride structure.