Allotropes of Carbon for edexcel 2008 onwards chemistry

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The Allotropes of Carbon
The allotropes of carbon are the different structural configurations that carbon can form in. Some
examples are graphite, diamond, fullerenes and carbon nanotubes. These all have different
applications and as nanotechnology improves as does the uses and efficiency.
Diamond is one of the most well known allotropes of carbon. It is formed under the Earth's surface
over many millions of years under extreme conditions. It is used industrially and for its `gleaming'
quality for jewellery. It is the hardest natural mineral on Earth and this is due to its carbon structure.
Each carbon atom covalently bonds to four other carbon atoms
which give it such a firm and rigid structure. It forms so strongly
that it cannot be scratched and so is used for drill bits, cutting
grinding and polishing. All of the bonds in diamonds are
directional, so stress can break the structure. This means that
diamonds are not very malleable and are in some respects
brittle. No electrons are free to move in the structure as all
valence electrons are used in the bonding. The electrons are
located between the nuclei being bonded together in each case.
Due to the formation of diamond it is also insoluble in water and
has a very high melting point, the many covalent bonds hold very
strongly requiring huge amounts of energy to break them.
Graphite is another common form of carbon arrangement. It is considered the basic arrangement for
carbon atoms to form in as other arrangements such as diamonds will very slowly decompose into
this structure (over millions of years). Graphite structure is that
each carbon atom only bonds to 3 other carbon atoms, this
forms layers as in the diagram and the layers are weakly
connected by Van der Waal forces. This layered quality makes
graphite soft and slippery and so powdered form is often used
as a lubricant. The bonds are directional across the layers
which mean that it is brittle and can break easily. As each
carbon atom is only joined to 3 others one electron is
delocalised and so in the area between layers. The many
covalent molecules mean that graphite also has a very high
melting point and is insoluble in water. However these can be useful as graphite is used in pencil
making, crucibles for melting and moulding other metals, moderators in atomic reactors and for
some brake linings.
Fullerenes are small molecules of carbon that are shaped into spheres. The smallest fullerene has 60
carbon atoms arranged in a pattern similar to a football in pentagon and hexagons This would be
known as a Buckminsterfullerene as shown on the left. The
molecule is totally symmetrical and all angles are equal as well as
bond lengths. As there are few covalent bonds holding the structure
together the molecule is soft and slippery, the weak Van der Waal
forces are all that attracts them together. Therefore it is also brittle as
the crystals are weak and easily separated. It is an electrical insulator
Tom Baker 12ST1

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To melt fullerenes the Van der
Waal forces must be broken which is relatively easy as they are only weak forces so it has a low
melting point. Carbon nanotubes are simply cylindrical fullerenes. These tubes are microscopic in
both width and length ranging from less than a single micrometer to a few millimetres in length. They
range in form whether it is a completely uniform shape to the ends thinning out and being open or
closed at the ends.…read more


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