Introduction to Number of Atoms in a Unit Cell
That a crystal lattice comprises of several unit cells. In a unit cell, every constituent particle( atom, molecule or ion ) has a specific and fixed position called lattice site. We can calculate a number of atoms/molecules and ions in a unit cell easily by analyzing the nature and position of constituent particles in unit cells.
Image 2: The corners get only 1/8th part of atom(b) Body- centred Cubic Unit CellIn a body-centred unit cell, 8 atoms are located on the 8 corners and 1 atom is present at the center of the structure. So total atoms in the body-centred unit cell will be:Since 8 atoms are present at the corners, each will contribute 1/8th of the original volume of the cell. Thus in the body-centred cubic unit cell:
Total atoms present in a face-centred unit cell = 1 + 3 = 4 atoms
(d) End-centred Cubic Unit Cell
In end-centred cubic unit cell, 8 atoms are located on 8 corners of the cube and 1 atom each is present on two opposite faces of the cube.
Therefore in end-centred cubic unit cell
Image 4: Contribution of Atom in different unit cells
The table given below summarizes a total number of atoms present in a unit cell.
Image 5: Types of unit cells
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1. What is a unit cell? | ![]() |
2. How do you determine the number of atoms in a unit cell? | ![]() |
3. What factors affect the number of atoms in a unit cell? | ![]() |
4. How does the number of atoms in a unit cell affect the properties of a material? | ![]() |
5. Can the number of atoms in a unit cell be fractional? | ![]() |