In HCP, the [2D] Hexagonal packed layers are arranged in ABAB form. The same happens in Primitive Hexagonal Unit Cell. So does that mean they are the same? If not what differentiates one from the other?

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    $\begingroup$ Hi and welcome to SE. It's unclear what you are trying to ask. Please edit your post to explain clearly what your question is. $\endgroup$ – Aniruddha Deb May 23 '20 at 8:13
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    $\begingroup$ This is a homework question. We have a policy which states that ‎you should show your thoughts and/or efforts into solving the problem. It'll make us certain that ‎we aren't doing your homework for you. Otherwise, this question may get closed.‎ Please edit in your full reasoning or thoughts on this. $\endgroup$ – Zenix May 23 '20 at 8:20
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    $\begingroup$ Where is the difference between a crocodile and a dolphin? $\endgroup$ – Ivan Neretin May 23 '20 at 8:57
  • $\begingroup$ @IvanNeretin I made changes to the question. I hope now it's okay. $\endgroup$ – Priyanuj Bora May 23 '20 at 12:39
  • $\begingroup$ @Zenix NO! it's not a homework question, edited the question just now. Could you answer the question now?? $\endgroup$ – Priyanuj Bora May 23 '20 at 12:40

the same happens in primitive hexagonal unit cell

Herein lies the gap in your concept: The same does not happen in primitive hexagonal unit cell. Here's an image to clear things up

enter image description hereenter image description here

The left one is a primitive hexagonal unit cell whereas the right one is a HCP lattice. To use your terminology, a simple primitive cell has packing of the type AAAA.. whereas a HCP cell has packing of the type ABAB..

I highly recommend reading your textbook or referring to some more material on solid state chemistry, such as this SlideShare presentation on basic crystallography.

  • $\begingroup$ So from 2d hexagonal packed layers we can make 1) HCP and 2)CCP but not Primitive Hexagonal Unit Cell?? $\endgroup$ – Priyanuj Bora May 23 '20 at 12:56
  • $\begingroup$ Yes you can. How to do so is an exercise left for the reader. $\endgroup$ – Aniruddha Deb May 23 '20 at 13:00
  • $\begingroup$ the second part of the question, can Primitive Hexagonal Unit Cell be made in the same way by arranging the 2D hexagonal layers in AAA type?? $\endgroup$ – Priyanuj Bora May 23 '20 at 13:01
  • $\begingroup$ The answer to this last question of yours is already here on this page, a few lines above. $\endgroup$ – Ivan Neretin May 23 '20 at 13:39
  • $\begingroup$ There is no such thing as an HCP lattice in terms of classifying symmetry. HCP is a primitive hexagonal structure with two atoms in the primitive cell (one per asymmetric unit). See chemistry.stackexchange.com/a/134572 $\endgroup$ – Karsten Theis Jun 3 '20 at 21:49

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