Diamond
The
allotropes of carbon include diamond, graphite and
buckminsterfullerene. Diamond is the most hard, most dense and the
least reactive of all the allotropes, it also has no colour. Its
properties can be explained by the arrangement of bonds and atoms
(figure 1).
Figure 1. Diamond
There
are two types of diamond, the most rare has atoms which are very
close to one another in the form of a hexagon, and the classic
diamond, which has a cubic close packed structure, thus the atoms
are also close to one another. Each atom has a coordination number
of four so the atoms are arranged in a tetrahedral structure. The
carbon atoms are linked with single bonds.
The
difference between the two polymorphs is the structure of the
carbon. Carbon, when it exists in the form of a cyclic six membered
ring can change its geometry according to the energy of the molecule
and the other atoms around it. It can hold the position of a chair
or a boat (figure 2).
The
chair is the most stable because the position had the least energy,
all the atoms in cubic diamond have this structure. Sometimes,
however the conformation can change and some hexagons take the form
of the boat, thus the structure of diamond changes. Diamond is an
insulator because of the separation of energy (greater than three
electron volts) between the highest of filled bands and lowest of
unfilled bands in the band theory diagram. Diamond is used for the
tips of drills, other industrial appliances where such strength is
required, and of course jewellery.
Home ||
Diamond ||
Graphite ||
Buckyballs ||
Nanotubes ||
Fullerenes
Conclusion ||
Glossary ||
References ||
Links
Samantha Shanley, School of Chemistry, University of Bristol
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