Do all solids have a crystalline organized structure?

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  • Thread starter fog37
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  • #1
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Dear Forum,

I know that in a solid molecules have a more compact organization. Are molecules arranged in a periodic structure, i.e. a crystal, in all solids? Do all solid have a crystalline organized structure?

Polymers exhibit crystal organization of the same type only over small finite regions.

thanks,
fog37
 

Answers and Replies

  • #2
marcusl
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No, a large class of solids are amorphous, which means that they lack a regular long-range structure. Glass is a common example.
 
  • #3
Dear Forum,

I know that in a solid molecules have a more compact organization. Are molecules arranged in a periodic structure, i.e. a crystal, in all solids? Do all solid have a crystalline organized structure?

Polymers exhibit crystal organization of the same type only over small finite regions.

thanks,
fog37
No, all solids don't have a 'crystalline structure'. Such solids are called amorphous solids for example, glass, cellophane. Amorphous solids don't have any sort of order or pattern in the arrangement of the molecules, though there might occasionally be a small region( crystallites) of 'regular packing'.
http://chemwiki.ucdavis.edu/?title=...olids/12.1:_Crystalline_and_Amorphous_Solids/
 
  • #4
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Glass, which is an amorphous solids, is often described as a liquid with a huge viscosity.

What about solid metals like iron, aluminum, etc.? Is their internal structure highly organized and repetitive, i.e. crystalline ?
 
  • #5
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From Brittanica.com:

  1. "Metals are usually crystalline solids. In most cases, they have a relatively simple crystal structure distinguished by a close packing of atoms and a high degree of symmetry."
But a chunk of metal consists of many grains (within which there is crystalline order). Across the grain boundary the crystallinity is broken.
 
  • #6
Vanadium 50
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Trying to shoehorn a college-level understanding of matter into the 3rd grade categories of solid, liquid and gas is unlikely to be successful.
 
  • #7
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From Brittanica.com:

  1. "Metals are usually crystalline solids. In most cases, they have a relatively simple crystal structure distinguished by a close packing of atoms and a high degree of symmetry."
But a chunk of metal consists of many grains (within which there is crystalline order). Across the grain boundary the crystallinity is broken.
Hi Espen-4. I see what you are saying. But why a chunk of metal is made of many neighboring grains where we find crystallinity and not throughout the entire chuck? Does it have to do with the way real metals are made?
 
  • #9
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According to this site (nice figures there): https://www.nde-ed.org/EducationResources/CommunityCollege/Materials/Structure/solidification.htm
grains form for the following reason: When the material goes from a liquid to a solid there are many nucleation points each forming a grain. They then grow in size until they come into contact with another grain. You end up with a material with grains.
You can make single crystals, but you need much more control of the solidification process in order to have nucleation starting only once, resulting in only one grain that cover the entire material. Semiconductors are often single crystals because the devices made from semiconductors (often) become inferior if the semiconductor isn't single crystal.
 
  • #10
DrDu
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Yes, that true. Nevertheless it is quite easy to grow nice macroscopic metal cyrstals yourself. You can grow nice crystal-trees electrolytically.
 
  • #11
ogg
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Feynman's Lectures famously claims (as wrong as wrong can be!) that solids are crystalline. The solid state ranges from highly ordered crystals to quasi-crystalline materials as well as semi-crystalline (polymer) solids to amorphous (glasses). It is possible to grow large crystals of most metals, but the expense can be excessive. You need special ovens with specially lined surfaces able to very slowly cool down the molten metal (which often needs to be very pure). But, "order" is not a well defined term. Quasi-crystals exist because we observed patterns in x-ray data which could only come from "impossible" crystals, so we had to make the concept of "order" more general. When I was in H.S., my chemistry lab project (w/2 lab partners) was to grow a CuSO4 crystal. It took several months but we ended up with one ~~ 4.5 x 0.8 x 2.5 inches. (Since CuSO4 is toxic, you probably wouldn't be allowed do that now days) Anyway, it was deep blue and quite pretty.
 
  • #12
ogg
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OTOH, imagine a very large (all sides 1 mile) box filled with rigid plastic figures (dolls). The question is, even if they were randomly tossed into the box, would there be any order or arrangement? Answer is: there might be. If some configurations repeated often enough, then even if not all of the dolls were in that "pattern", we'd say that it had a statistical arrangement (or order). So, the question becomes whether we have a large enough sample to "see" the arrangement, and whether the solid is sufficiently cold so that the arrangements aren't changing. It's a tricky thing when you dig into the details...
 

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