All websites say the answer should be 3 , however shouldn't it be four ?
- Primitive
- BCC
- CCP
- End Centered
$\begingroup$
$\endgroup$
3
-
4$\begingroup$ What's end centered? If you mean base centered, then it is not cubic. $\endgroup$– Ivan NeretinCommented Jul 24, 2023 at 11:54
-
2$\begingroup$ Could you edit the question to give some context? The question asks about the number of atoms (or arrangements of atoms, not clear), but then then it asks to choose one of four different centering operations. It would be nice to see the original question or some more background. Googling I learned that polonium crystallizes in a primitive cubic structure, which is otherwise rare for simple structures. $\endgroup$– Karsten ♦Commented Jul 24, 2023 at 15:08
-
$\begingroup$ CS, FCC, BCC : en.wikipedia.org/wiki/Cubic_crystal_system $\endgroup$– M06-2xCommented Jul 24, 2023 at 15:21
Add a comment
|
2 Answers
$\begingroup$
$\endgroup$
2
End-centered or base-centered cubic actually defaults to face-centered cubic.
Start with a cubic arrangement having eight points at the vertices. To make the end-centered or base-centered cube you add two points at the centers of a pair of opposing faces. But then cubic symmetry, by definition, requires retaining a threefold symmetry axis around a body diagonal of the cube. With the additional pair of points on the faces you identified as bases, this is possible only if you also place points at the centers of the other two opposing face-pairs, and then your array has become face-centered cubic.
answered Jul 24, 2023 at 12:35
-
$\begingroup$ Or you could say it does not exist. Once you have centering on one face, you also have it on the others. $\endgroup$– Karsten ♦Commented Jul 24, 2023 at 15:39
-
1$\begingroup$ The idea behind my logic is to explain why a separare end-centered cubic lattice fails to hold up. $\endgroup$ Commented Jul 24, 2023 at 16:19
$\begingroup$
$\endgroup$
In cubic system how many atoms arrangement exist in nature?
There is no limit to the number of atoms. Below is an example of a plant protein (PDB 1eav) crystallizing in space group $\ce{P 2_1 3}$. It is a primitive setting, and there are lots of atoms (some are disordered water molecules, not shown) in a huge unit cell:
The image is a cross-eyed stereo diagram. If you look at it at a typical viewing distance and then focus on a object (like your index finger) about 10 cm - 15 cm away, the two pictures overlap. Some people are able to focus on the figure while keeping the eyes crossed, achieving a 3D effect. Others need special glasses and the images reversed (for wall-eyed viewing).
Stereo or not, you can see the 3-fold axis along the space-diagonal of the cube, demonstrating that the crystal is cubic. As there is no centering, it is primitive cubic, but centered cubic space groups exist as well.
