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Siddharth Srivastava posted an Question
May 23, 2021 • 18:15 pm
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30 points
30 points
- IIT JAM
- Chemistry (CY)
Can you explain elements of symmetry in cubic lattice ?
can you explain elements of symmetry in cubic lattice ? how do we know tha pos( plane of symmetry) and cos ( centre of symmetry ) have been arranged ?
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Priyanshu kumar![best-answer]()
Plane of symmetry: It is an imaginary plane which passes through the molecule and divides it into two equal portions which are exactly the superimposable mirror images of each other. There are 9 plane of symmetry in cubic crystal as you can see in attached image. An axis of symmetry can only passes through (1) mid-points of two opposite edges. (As a cube has 12 edges, there are 12÷2=6 axes of this type.) (2) two opposite vertices. (As a cube has 8 vertices, there are 8÷2=4 axes of this type.) (3) the centres of two opposite faces. (As a cube has 6 faces, there are 6÷2=3 axes of this type.) So it has 13 axes of symmetry. Centre of symmetry: It is an imaginary point in the crystal that any line drawn through it intersects the surface of the crystal at equal distance on either side. A cubic crystal possesses total 23 elements of symmetry. Plane of symmetry (3 + 6) = 9 Axes of symmetry (3 + 4 + 6) = 13 Centre of symmetry (1) = 1 Total symmetry = 23