define unit cell.classify unit cell on the basis of no. of atoms present per unit cell.
Answers
Answer:
Unit cells can be defined as the simplest and smallest part of a crystal lattice.
On the basis of atoms present per unit cell, they are classified as
1. primitive unit cell
2. Centred unit cell
a. body entered
b. face centred
c. End centred unit cell.
Answer:
- The smallest repeating unit of the crystal lattice is the unit cell, the building block of a crystal.
- A unit cell can either be primitive cubic, body-centred cubic (BCC) or face-centred cubic (FCC).
Explanation:
1. Primitive Cubic Unit Cell
In the primitive cubic unit cell, the atoms are present only at the corners. Every atom at the corner is shared among 8 adjacent unit cells. There are 4 unit cells in the same layer and 4 in the upper (or lower) layer. Therefore, a particular unit cell has the only 1/8th of an atom. Each small sphere in the following figure represents the centre of a particle that occupies that particular position and not its size.
2. Body-centred Cubic Unit Cell (BCC)
A BCC unit cell has atoms at each corner of the cube and an atom at the centre of the structure. The diagram shown below is an open structure. According to this structure, the atom at the body centre wholly belongs to the unit cell in which it is present.
3. Face-centred Cubic Unit Cell (FCC)
An FCC unit cell contains atoms at all the corners of the crystal lattice and at the centre of all the faces of the cube. The atom present at the face-centered is shared between 2 adjacent unit cells and only 1/2 of each atom belongs to an individual cell.