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STRUCTURE OF DIAMOND,GRAPHITE AND FULLERENE WITH EXPLANATION<br />MADE BY:-<br /> RAFIYA SIRIN<br /> XI-B<br />
ALLOTROPES<br />The phenomenon of existence of an element in two or more forms which have different physical properties but identical chemical properties is called allotropy and the different forms are called allotropes.<br />
DIAMOND<br />A diamond is a transparent crystal of tetrahedrally bonded carbon atoms (sp3) that crystallizes into the diamondlattice which is a variation of the facecentered cubic structure.<br />Each carbon atom joins four other carbon atoms in regular tetrahedrons (triangular prisms). Based on the cubic form and its highly symmetrical arrangement of atoms, diamond crystals can develop into several different shapes, known as 'crystal habits'.<br />
STRUCTURE OF DIAMOND<br />Atomic carbon has an atomic number of 6 and a 122 electronic ground state configuration. The carbon atom's electronic configuration is believed to change from its ground state in diamond as follow: <br />Each carbon atom is covalently bonded with four other carbon atoms. These four atoms are again strongly bonded with other four carbon atoms. All the bonds are sp3 hybridized. The sigma ( ) bonds formed, have maximum electronic overlap with each other. The bond angles are at 109o28’ with each other. The structure formed is therefore very rigid. This makes diamond one of the hardest substances that are found naturally. <br />
The SP3 hybridized orbital has a tetrahedral symmetry <br />HYBRIDISATION IN DIAMOND..<br />
GRAPHITE<br />In graphite, carbon is sp2 hybridized. Each carbon is thus linked to three other carbon atoms forming hexagonal rings. Thus it has a two-dimensional sheet like structure consisting of a number of benzene rings fused together. The various sheets are held together by weak van der waals’ forces of attraction.<br />
STRUCTURE OF GRAPHITE<br />In going from its ground state to the graphite structure, a carbon atom's electronic configuration is believed to change as follows: <br />Three of the two 2s and two 2p electrons in carbon's ground state redistribute into three hybrid 2 sp2 orbitals which are a mathematical mixing of the orbitals with two of the three orbitals. The angular probabilities for these 2 sp2 orbitals can be represented by three coplanar lobes at 120 to each other. The fourth electron of the original two 2s and two 2p electrons fills that p orbital which does not participate in the 2sp2 hybrid, the lobe for this orbital being perpendicular to the plane defined by the three 2sp2 orbitals. <br />
STRUCTURE OF GRAPHITE<br />These sheets are held together by weak van der waals force of attraction..<br />
FULLERENES<br />A fullerene is any molecule composed entirely of carbon, in the form of a hollow sphere, ellipsoid, or tube. Spherical fullerenes are also called buckyballs, and cylindrical ones are called carbonnanotubes or buckytubes. Fullerenes are similar in structure to graphite, which is composed of stacked graphene sheets of linked hexagonal rings; but they may also contain pentagonal (or sometimes heptagonal) rings.<br />
STRUCTURE OF FULLERENES<br /> Each carbon is part of one pentagon and two hexagons, each has two single bonds and one double bond for the traditional carbon valence of four. Heeding the principles of the VSEPR theory, we would say that each carbon has Sp2 hybridization with the remaining p-orbital available for pi-bonding with one of the adjacent carbon atoms. To summarize, each carbon forms three sigma-bonds with its Sp2 hybrid orbitals and one pi-bond with the remaining p orbital. <br />