A unit cell is a term related to crystal structure. (a) What do you m

1.	A unit cell is a term related to crystal structure. (a) What do you mean by unit cell?(b) Name any two types of cubic unit cells.(c) Calculate the number of atoms in each of the above – mentioned cubic unit cells.(d) Identify the substance which shows Frenkel defect:(i) NaCI(ii) KCI(iii) ZnS(iv) AgBr
Answer» (a) Unit cell is the smallest portion of a crystal lattice which, when repeated in different directions, generates the entire lattice. (b) Simple cubic unit cell, body centred cubic (bcc) unit cell, face centred cubic (fee) unit cell (any two) (c) Number of atoms per unit cell (i) Simple cubic unit cell: Total number of atoms in one unit cell =8× \(\frac{1}{8}\) =1 atom (ii) Body centred cubic (bcc) unit cell: Total number of atoms in one unit cell =(8× \(\frac{1}{8}\))+(1×1)=1+1=2 atoms (iii) Face centred cubic (fee) unit cell: Total number of atoms in one unit cell =(8×\(\frac{1}{8}\))+(6× \(\frac{1}{2}\)) = 1+3 = 4 (any two required) (d) ZnS or AgBr (AgBr shows both Schottky and Frenkel defects)

A unit cell is a term related to crystal structure. (a) What do you mean by unit cell?(b) Name any two types of cubic unit cells.(c) Calculate the number of atoms in each of the above – mentioned cubic unit cells.(d) Identify the substance which shows Frenkel defect:(i) NaCI(ii) KCI(iii) ZnS(iv) AgBr

Answer»

(a) Unit cell is the smallest portion of a crystal lattice which, when repeated in different directions, generates the entire lattice.

(b) Simple cubic unit cell, body centred cubic (bcc) unit cell, face centred cubic (fee) unit cell (any two)

(i) Simple cubic unit cell:

Total number of atoms in one unit cell =8× \(\frac{1}{8}\) =1 atom

(ii) Body centred cubic (bcc) unit cell:

Total number of atoms in one unit cell

=(8× \(\frac{1}{8}\))+(1×1)=1+1=2 atoms

(iii) Face centred cubic (fee) unit cell: Total number of atoms in one unit cell

=(8×\(\frac{1}{8}\))+(6× \(\frac{1}{2}\)) = 1+3 = 4

(any two required)

(d) ZnS or AgBr

(AgBr shows both Schottky and Frenkel defects)