Ncert Exercises & Solutions

1.12 Distinguish between

(i) Hexagonal and monoclinic unit cells

(ii) Face-centred and end-centred unit cells.

(i) Hexagonal unit cell
For a hexagonal unit cell,

a = b \neq c

and α = β = 90 °

γ = 120 °

Monoclinic unit cell
For a monoclinic cell,

a \neq b \neq c

and α = γ = 90 °

β \neq 90 °

(ii) Face-centred unit cell
In a face-centred unit cell, the constituent particles are present at the corners and one at the centre of each face.

End-centred unit cell

An end-centred unit cell contains particles at the corners and one at the centre of any two opposite faces.