Question

Answer 1

Unit cell: An imaginary parallel sided region from which the entire crystal can be built up is called as unit cell. The unit cell is built up by purely translational displacements.

Crystal lattice is the geometrical pattern of the arrangement of unit cells. In a crystal lattice, edges of the unit cells represent lattice vectors. Each lattice point shows indistinguishable environment.

(a)

Given two structures are having different patterns of packing and different types of spheres. So, the two-dimensional unit cells can be drawn as shown below:

(b)

Determination of angle between the lattice vectors as shown below:

From the above two-dimensional unit cells,

Figure (i) is a square lattice which results when the lattice vectors are equal in length and perpendicular to each other. Here, the lattice vectors are ‘a’ and ‘b’ then

Figure (ii) is a hexagonal lattice and their lattice vectors are equal in length and are having angle between them. Therefore,

(c)

Here (i) is a square type lattice where as (ii) is a hexagonal lattice.