CBSE Class 12-science Answered
What is three fold axis in case of ABCABC……. or CCP (cubic close packing) in 3 dimentions?
What is six fold axis incase of ABAB…..or hexagonal close packing (hcp) in three dimention?
What is meaning of statement given below-“In hexagonal unit cell three unit cells are shown to give hexagon.”
What is difference between BBC and HCP since both are of ABAB…. Type
Explain in detail with diagram
Asked by shubham.padamwar.3 | 21 Dec, 2014, 12:38: PM
Expert Answer
Dear shubham.padamwar.3@facebook.com
Thanks for asking us a question in Ask the Expert section of TopperLearning.com.
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Answer 1: In case of ABC ABC ABC……arrangement of CCP structure 3-fold axis of symmetry is observed which means the crystal has same appearance on rotation through an angle of 120°. This axis passes through the diagonal of the cube.
Answer 2: In case of AB AB AB....arrangement of HCP structure 6-fold axis of symmetry is observed which menas the crystal has same appearance on rotation through an angle of 60°. This axis passes through the centre of the structure.
Answer 3: In hexagonal unit cell three unit cells are shown to give hexagon because cell of an HCP lattice is visualized as a top and bottom plane of 7 atoms, forming a regular hexagon around a central atom. In between these planes is a half hexagon of 3 atoms.
Answer 4: Coordination number and atoms in unit cell for BCC is 8 and 2 while for HCP it 12 and 6. This is the main difference inbetween BCC and HCP.
Regards
Topperlearning Team.
Answered by Arvind Diwale | 25 Dec, 2014, 09:27: PM
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