How many unit cells are present in a cubic -shaped ideal crystal of NaCl of mass 1.00 g [Atomic masses: Na= 23, Cl = 35.5]
2.57×1021 unit cells
NaCl⇒Cl− occupies corners and face centres ⇒ Effectively 4Cl− ions
Na+ occupies octahedral voids.
⇒ Effectively 4Na+ions.
⇒ 1 unit cell has effectively 4 molecules of NaCl.
mass of unit cell =4×mass (NaCl)6.023×1023=4×58.56.023×1023
⇒ No. of unit cell in 1g=1g4×58.56.023×1023=2.57×1021 unit cells