Number of Atoms in a Unit Cell – Class 12 | Chapter – 1 | Chemistry Short Notes Series PDF for NEET & JEE
Number of Atoms in a Unit Cell: The number of atoms in a unit cell of a crystal depends on the crystal’s structure, which is determined by the arrangement of atoms or molecules in the crystal lattice. A unit cell is the smallest repeating unit of the crystal lattice, and it contains all the information about the crystal structure, including the number and type of atoms or molecules present.
It’s important to note that the number of atoms in a unit cell can vary depending on the chemical composition of the crystal. Different elements or molecules may occupy different positions in the unit cell, resulting in a different number of atoms. Additionally, there are other types of unit cells, such as hexagonal close-packed and cubic close-packed, which have different numbers of atoms in their unit cells. The determination of the number of atoms in a unit cell is a critical step in understanding the crystal structure and its properties.
Number of Atoms in a Unit Cell Types
There are three main types of unit cells: primitive, body-centered, and face-centered.
- Primitive unit cell: A primitive unit cell contains only one lattice point or one atom at its corners. Therefore, the number of atoms in a primitive unit cell is equal to one.
- Body-centered unit cell: A body-centered unit cell contains one lattice point or one atom at each of its corners and one additional atom at the center of the cell. Therefore, the number of atoms in a body-centered unit cell is equal to two.
- Face-centered unit cell: A face-centered unit cell contains one lattice point or one atom at each of its corners and one additional atom at the center of each face of the unit cell. Therefore, the number of atoms in a face-centered unit cell is equal to four.
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