How many bravais lattices are present in total of seven crystal systems?
Answer & explanation
Correct answer: option 2
There are four types of unit cell
(i) Primitive (Simple): Lattice points are at corners.
(ii) Face-centred: Lattice points are at corners and at face-centres.
(iii) Body-centred: Lattice points are at corners and at body-centres.
(iv) End-face centred: Lattice points are at corners and at end-faces.
Seven types of crystal systems exist.
Total number of arrangements = 7 x 4 = 28
But only 14 of these arrangements exist, because for these arrangement of atoms, force of attraction > force of repulsion.
In rest of fourteen, repulsion > attraction.
Hence, only 14 Bravais lattices are present in 7 crystal systems.