Allotropes of Carbon: Diamond and Graphite

Transport Phenomenon (Electrical and Thermal) in two allotropic forms of Carbon (Diamond and Graphite) Graphite and Diamond both are formed from carbon (two allotropic forms of carbon). Though they have similar constituent element, they differ a lot in their properties. Diamond is a good thermal conductor but a bad electrical conductor, while graphite is a bad thermal conductor but a good electrical conductor. This is one example of their property difference. The difference in their properties arises because of different arrangement of carbon atoms present in them. Basic physical and chemical properties of graphite and diamond to highlight their differences are as follows: Differences between Graphite and Diamond Physical Appearance: Graphite is opaque and metallic- to earthy-looking while diamonds are transparent and brilliant. Another important physical difference is their hardness. The hardness of minerals is compared using the Moh's Hardness Scale, a relative scale numbered 1 (softest) to 10 (hardest). Graphite is very soft and has a hardness of 1 to 2 on this scale. Diamonds are the hardest known natural substance and have a hardness of 10. Diamond is used as an abrasive because of its great hardness, whereas graphite is used as a lubricant. Structural Differences: Diamond Space Group Fd3m face-centered cubic Atoms/unit cell 8 Cell volume 45.385 x 10-24cm3 X-ray density 3.5155 g/cm3 {draw:frame} Graphite Space Group C6/mmc; C-centered hexagonal Lattice parameters a = 2.4612 Å c = 6.7079 Å Atoms/unit cell 4 Cell volume 35.189 x 10-24cm3 X-ray density 2.2670 g/cm3 Electronic Configuration: Diamond The carbon atom's electronic configuration is believed to change from its ground state in diamond as follow: {draw:frame} Quantum-mechanical calculations indicate that greater overlap between orbitals results in a stronger covalent bond. The diamond structure represents a three-dimensional