The allotropes of carbon

Until now, naturally, the carbon was known to all in two crystalline forms:

• Diamonds
• Graphite

Diamonds

Diamond, the hardest mineral is transparent that exists today, has been identified as a crystalline form of carbon and Taking Notes in the late 18th century.
From the viewpoint of its structure, each carbon atom bound to four neighboring atoms scattered on top of a tetrahedral structure, this geometry is due to the hybridization state of carbon (sp3) angles, which requires 109 '28. Each atom form four covalent bonds in space with a bond length of 0.136nm. Their tetrahedral symmetry sign of a strong dense and anisotropic with links cc very hard to break, and a melting temperature of about 3500 degrees.
The electrons are confined in the covalent bonds, they can not move and thus the diamond will be a very bad driver.


Diamond structure

Graphite    (Formerly "plumbago")

From the Greek graphein (write with a pencil or a mine), graphite consists of layers of planar benzene rings linked together like a "rabbit fence", where each carbon atom is connected to three of its neighbors by making connections 120degrés angles (this geometry is explained here by the sp2 hybridization of these atoms). It should be noted here that the flat connections are strong and characterized by distances between atoms 0.142nm, but conversely the connections between each level benzene are very low ... they are through Van der Waals forces which are and low electrical forces act at very short distances.
Here the electrons of these layers being relocated, (benzenoid structure) and given the strength of van der Waals interaction between layers (everything does have an attractive force at close range (1/x7)), electrons can here move and the driver is graphite.


Sheet structure of graphite
It is noted here by observing the pattern of the structure of graphite crystal that is very fragile because the sheets can slide over each other. (This is obviously due to the weak Van der Waals forces).

The third crystalline form of carbon: Fullerene

In 1985, an unexpected discovery as researchers had expected only exceptionally very far from imagining the future impact of their research.
The team consisting of H. Kroto, Smalley and R. Rfcurl sprayed graphite laser in a chamber filled with helium, and is analyzing the residue of the experience they have observed in a mass spectrometer that molecules with 60 carbon atoms were formed and after some research they have had to infer that these molecules have a closed cage structure.
This structure that mathematicians call an iso truncated octahedron made up of facets, these facets are they even hexagons or pentagons.
The name "Fullerene" comes from the name of a German architect (Buckminster Fuller) who built for the Universal Exhibition of Canada a geodesic dome made of hexagon and pentagon.


Structure of a fullerene
Geometry: Fullerenes have the shape of a polyhedron, which can be characterized for the number of polygons covering the surface. These, the number of F, total V vertices and A edges. There is a relationship between these three numbers called Euler relation.
S-A + F = 2 (G.1)
The number 2 will match the topology of a sphere. If you try to make a polyhedron with H and P pentagons pentagons we have:
F = P + H (G.2)
2A +5 P = 6H (G.3)
3S = 6H +5 P (G.4)
The factor 2 in (.3 G) comes from the fact that an edge is shared by two pentagons,. Similarly, the factor 3 in (G.4) from the summit is a common three polygons. Substituting these equations into (G.1) we obtain
P = 12
The value of H will depend on the conditions that we are given for S.
Fullerenes have remarkable properties in many respects, these properties are defined as the ratio between the number of pentagon and hexagon number, a percentage that will always respect the rule of Euler.
Fullerenes have the distinction of being hollow atomic assemblies, we can introduce foreign atoms, including metal (Ni, Na, K, Rb, Cs).
A room temperature, the C60 molecules can rotate freely independently of each other.
When the temperature decreases, a phase change to a simple cubic structure occurs around 250 ° K.
In crystal structure, we can also introduce foreign atoms (K, Br, ...) some compounds thus obtained will be low temperature superconducting
It is also important to note that in comparison with the graphite and diamond, the carbon atoms will be here in a state through hybridization between sp2 and sp3, this is due to the shape of a fullerene sphere.
In 1990, the molecule whose simplicity of implementation across the laboratory can produce them quickly, leads W. Kratschmer and DR Huffman to develop a method for synthesis of this molecule is therefore occurring in the world. Since this year the amounts necessary to study the properties of the molecule is no longer a problem.