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Carbon (Latin word: carbo “coal”) is a chemical element with symbol C belongs to group 14 of the periodic table. Its atomic number is 6 and has the electronic structure of 1s²2s²2p². The valence of carbon will depend upon the arrangement of electrons in 2s and 2p orbitals. 2s orbitals are supposed to house maximum of 2 electrons and 2p can possess a maximum of 6 electrons. The energy of electrons in 2s and 2p orbitals is not much different from each other. Therefore, depending upon the condition of the electronic arrangement, carbon atom can show valence of 2 due to hybridization of 2s¹ 2p¹ orbitals. The 2s2p orbital can also be hybridized as 2s¹2p² showing a valence of 3. Likewise, 2s2p orbital can be hybridized to show 2s¹2p³ configuration making a carbon valence of 4. Carbon compound with 2s¹2p¹, i.e., with valence of 2, is rarely seen, and if some carbon compounds are made with such configuration, they are not stable. Most common compounds with configuration of 2s¹2p² (like graphite) and 2s¹2p³ (like diamond) are found in nature. Angles between each carbon for 2s¹2p¹, 2s¹2p² and 2s¹2p³ are shown in Figure 1.1.

Figure 1.1 The formation angle between the carbon for sp, sp² and sp³ configuration.

In this chapter we shall restrict our discussions to carbon with configuration of sp² and sp³. In addition, we shall also restrict our discussions especially regarding carbon fiber (discussed in detail in later on), though we may touch upon carbon nanotube.

It will not be the scope of this chapter to discuss diamond or graphite, mainly because information about these materials are available in almost all textbooks dealing with carbon. Our discussion will be confined to materials like carbon fiber, carbon nanofibers and to some extent carbon nanotubes for making a clear distinction between these materials.