What is unit cell? Explain classification of unit cell
Answers
Explanation:
Unit cell : the smallest group of atoms which has the overall symmetry of a crystal, and from which the entire lattice can be built up by repetition in three dimensions.
Types Of Unit Cell
There are two types of unit cells – Primitive and Centred Unit Cells.
Primitive Unit Cells:
When particles in unit cell are present only at the corners, it is called the primitive unit cell or the unit cell constructed so that it contains only one lattice point is called primitive cell means that there is n number of cells sharing the lattice point, each vertex of the cell sits on a lattice point which is shared with the surrounding cells and each lattice point is said to contribute 1/n to the total number of lattice points in the cell.
Answer:
unit cell ..
A unit cell is the most basic and least volume consuming repeating structure of any solid. It is used to visually simplify the crystalline patterns solids arrange themselves in. When the unit cell repeats itself, the network is called a lattice
A unit cell is the smallest repeating portion of a crystal lattice.
Unit cells occur in many different varieties. As one example, the cubic crystal system is composed of three different types of unit cells: (1) simple cubic , (2) face-centered cubic , and (3)body-centered cubic .
Three unit cells of the cubic crystal system. Each sphere represents an atom or an ion. In the simple cubic system, the atoms or ions are at the corners of the unit cell only. In the face-centered unit cell, there are also atoms or ions in the center of each of the six faces of the unit cell. In the body-centered unit cell, there is one atom or ion in the center of the unit cell in addition to the corner atoms or ions.
Pay special attention to the last diagram for each type of cell. You will notice that the atoms or ions at the edges of each face or at the corners are not complete spheres. In the simple cubic cell, each corner atom is shared by 8 differenent unit cells. The same situation exists for the edge or corner particles in the face-centered and body-centered cubic forms. In addition, each of the particles in the center of the face-centered cubic cell is shared by 2 unit cells. Body-centered cells have an additional atom in the middle of the cell which is contained entirely in that cell.
Note that we have only considered the unit cells of a cubic crystal. Other crystal forms also have unit cells. These unit cells are listed below:
rhombohedral, hexagonal, triclinic – one unique form each
tetragonal – simple and body-centered
monoclinic – simple and base-centered
orthorhombic – simple, face-centered, body-centered, base-centered