
What are primitive unit cells and what are non-primitive unit cells?
Answer
486.9k+ views
Hint: Unit cell is known to be the building block of crystal. It is the smallest portion of the crystal lattice. Knowing about unit cells very well will help us to understand what a primitive and non-primitive unit cell is.
Complete step by step answer:
First of all, we must know what is a crystal lattice and unit cell? Crystal lattice is the arrangement of atoms, ions or molecules in a symmetrical three-dimensional arrangement. We can also say it is a geometrical representation of atoms, ions or molecules. Smallest unit of the crystal lattice represents the unit cell.
Unit cell is defined as the smallest repeating portion of the crystal. It is the basic structural unit or building block of the crystal. Unit cells can be classified as primitive and non-primitive unit cells. Unit cells have two parameters namely: cell dimensions such as \[abc\] and interfacial angles such as \[\alpha \beta \gamma \].
- Primitive Unit cell:
A unit cell which has only one lattice point in the crystal are called primitive unit cells.
This lattice point is present on the edges or corner of the unit cell.
- Non-primitive unit cell:
When a unit cell has not only one lattice point at the corner but also additional lattice points are present it is called a non primitive unit cell. It is also known as a centred unit cell. There are three types of centred unit cells. They are
- Body centered
- Face centred
- End centered
Body centred:
When the atoms are present at the centre of the body of the crystal, it is called Body-centred.
Face-centred:
When atoms are present at the centre of the face of the crystal, it is called face-centred.
End-centered:
When the atoms are present at the centre of the opposite faces of the crystal, it is known as End-centred.
Additional information:
There are seven crystal systems and 14 Bravais lattices in this crystal system.
Note: - The arrangement of atoms in the crystal can sometimes cause some defects, these defects are of two types: stoichiometric and non-stoichiometric defects.
- Examples of stoichiometric defects are Frenkel and Schottky defects.
- Examples of non-stoichiometric defects are metal excess and metal deficiency defects.
Complete step by step answer:
First of all, we must know what is a crystal lattice and unit cell? Crystal lattice is the arrangement of atoms, ions or molecules in a symmetrical three-dimensional arrangement. We can also say it is a geometrical representation of atoms, ions or molecules. Smallest unit of the crystal lattice represents the unit cell.
Unit cell is defined as the smallest repeating portion of the crystal. It is the basic structural unit or building block of the crystal. Unit cells can be classified as primitive and non-primitive unit cells. Unit cells have two parameters namely: cell dimensions such as \[abc\] and interfacial angles such as \[\alpha \beta \gamma \].
- Primitive Unit cell:
A unit cell which has only one lattice point in the crystal are called primitive unit cells.
This lattice point is present on the edges or corner of the unit cell.
- Non-primitive unit cell:
When a unit cell has not only one lattice point at the corner but also additional lattice points are present it is called a non primitive unit cell. It is also known as a centred unit cell. There are three types of centred unit cells. They are
- Body centered
- Face centred
- End centered
Body centred:
When the atoms are present at the centre of the body of the crystal, it is called Body-centred.
Face-centred:
When atoms are present at the centre of the face of the crystal, it is called face-centred.
End-centered:
When the atoms are present at the centre of the opposite faces of the crystal, it is known as End-centred.
Additional information:
There are seven crystal systems and 14 Bravais lattices in this crystal system.
Crystal system | Bravais lattices | Cell dimensions | Interfacial angles |
Cubic | Primitive, Face-centered, Body-centered=3 | \[a=b=c\] | \[\alpha =\beta =\gamma =90{}^\circ \] |
Tetragonal | Primitive, Body-centered=2 | \[a=b\ne c\] | \[\alpha =\beta =\gamma =90{}^\circ \] |
Orthorhombic | Primitive, Face-centered, Body-centered, End-centered=4 | \[a\ne b\ne c\] | \[\alpha =\beta =\gamma =90{}^\circ \] |
Monoclinic | Primitive, End-centered=2 | \[a\ne b\ne c\] | \[\alpha =\gamma =90{}^\circ ,\beta \ne 90{}^\circ \] |
Triclinic | Primitive=1 | \[a\ne b\ne c\] | \[\alpha \ne \beta \ne \gamma \ne 90{}^\circ \] |
Hexagonal | Primitive=1 | \[a=b\ne c\] | \[\alpha =\beta =90{}^\circ ,\gamma =120{}^\circ \] |
Trigonal or Rhombohedral | Primitive=1 | \[a=b=c\] | \[\alpha =\beta =\gamma \ne 90{}^\circ \] |
Note: - The arrangement of atoms in the crystal can sometimes cause some defects, these defects are of two types: stoichiometric and non-stoichiometric defects.
- Examples of stoichiometric defects are Frenkel and Schottky defects.
- Examples of non-stoichiometric defects are metal excess and metal deficiency defects.
Recently Updated Pages
Master Class 12 Business Studies: Engaging Questions & Answers for Success

Master Class 12 Economics: Engaging Questions & Answers for Success

Master Class 12 Social Science: Engaging Questions & Answers for Success

Master Class 12 English: Engaging Questions & Answers for Success

Master Class 12 Maths: Engaging Questions & Answers for Success

Master Class 12 Physics: Engaging Questions & Answers for Success

Trending doubts
Draw a labelled sketch of the human eye class 12 physics CBSE

a Tabulate the differences in the characteristics of class 12 chemistry CBSE

Which one of the following is a true fish A Jellyfish class 12 biology CBSE

Why is the cell called the structural and functional class 12 biology CBSE

Differentiate between homogeneous and heterogeneous class 12 chemistry CBSE

Write the difference between solid liquid and gas class 12 chemistry CBSE
