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Asked by to Daren, Lynne, Phillip, Simon on 17 Jun 2014. This question was also asked by .
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anon answered on 17 Jun 2014:
Carbon comes in many different forms – when it’s just single atoms of carbon, it looks like soot, but a carbon atom can also join together with three others to form hexagonal sheets, which is graphene. Lots of these sheets on top of each other make graphite, which is in your pencils. Then there’s something called buckminsterfullerene, which is like a football made of carbon atoms.
Diamond is made when four carbon atoms join together. Under pressure it’s the most stable form of carbon so all the carbon atoms rush together to form this structure. Once you take the pressure off the diamond won’t change back because it’s so stable.See the different forms of carbon here: http://rimg.geoscienceworld.org/content/75/1/47/F1.large.jpg
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Phillip Manning answered on 17 Jun 2014:
When the carbon atoms are heated under immense pressure, the very atoms of carbon rearrange into the most stable/resistant from of carbon for that particular environment. Once dug-up, they do not revert to the former atomic arrangement, leaving us with a rather tough mineral.
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Lynne Thomas answered on 17 Jun 2014:
When something is put under extreme pressure, its volume is much smaller. This means that the atoms have to rearrange themselves to fit together in a more efficient way. When this happens with carbon, it changes from strong bonds (called covalent bonds) in two dimensions to strong bonds in three dimensions as all the atoms are forced to be closer together. Because these are strong bonds, when you take the pressure off, the diamond stays as it is and is incredibly strong because of the three-dimensional strong bonds. Think about the triangle – this is an incredibly strong shape!
It is quite amazing that even though diamond and graphite are both made of just carbon atoms, that the way the look and how strong they are is so different! A pencil made out of diamond would just rip holes in your paper and leave no writing behind! This is because of how the atoms are connected in the solid.
If you take some graphite from something like your pencil and stick some sellotape on it and then pull it off quickly, the stuff on the sellotape is called graphene and it is a single layer of graphite carbon. It is potentially a very useful material as it is very good at conducting electricity and there is a lot of research going on now to find out how we can use it.
We can also make things called carbon nanotubes that can act as very small electronic wires. All of these things are just made of one element, carbon!
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Daren Fearon answered on 17 Jun 2014:
Carbon can take many different forms, the most stable being diamond but others being graphite or soot. Apply enough energy to something (like by applying pressure) and you can get it to it’s most stable form from which it won’t change back easily.
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Simon Redfern answered on 17 Jun 2014:
carbon turns into diamond at high pressure because the most stable structure on increasing pressure is the one that takes up least space per atom. That also means it is the densest. Carbon can exist as graphite (which you find in your pencil lead), as soot, or as graphene. All of these forms of carbon are quite low density (the volume per atom is relatively large). Diamond has a much higher density than all of the other forms of carbon, and this is why it is the structure of carbon that exists at high pressure. Diamond is the hardest known material, and probably occurs quite commonly in parts of the deep Earth.
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