Carbon Allotropes and Compounds

The primary objective of this book is the study of the element carbon itself and its polymorphs, i.e., graphite, diamond, fullerenes, and other less common forms. These allotropes (or polymorphs) have the same building block, the carbon atom, but their physical form, i.e., the way the building blocks are put together, is different. In other words, they have distinct molecular or crystalline forms. 

The capability of an element to combine its atoms to form such allotropes is not unique to carbon. Other elements in the fourth column of the periodic table, silicon, germcinium, and tin, also have that characteristic. However carbon is unique in the number and the variety of its allotropes. 

The properties of the various carbon allotropes can vary widely. For instance, diamond is by far the hardest-known material, while graphite can be one of the softest. Diamond is transparent to the visible spectrum, while graphite is opaque diamond is an electrical insulator while graphite is a conductor, and the fullerenes are different from either one. Yet these materials are made of the Scime Ceirbon atoms the disparity is the result of different arrangements of their atomic structure. 

Just as carbon unites easily with iteelf to form polymorphs, it can also combine with hydrogen and other elements to give rise to ein extraordinary number of compounds and isomers (i.e., compounds with the same composition but with different structures). The compounds of carbon and hydrogen and their derivatives form the extremely large and complex branch of chemistry known as organic chemistry. More than half-a-million organic compounds are identified and new ones are continuously discovered. In fact, far more carbon compounds exist than the compounds of all other elements put together.  

While organic chemistry is not a subject of this book, it cannot be overlooked since organic compounds play a major part in the processing of carbon polymorphs. Some examples of organic precursors are shown in Table 2.1.PI 

---

In addition to the sp -tetragonal hybrid orbital reviewed in Sec. 3 above, two other orbitals complete the series of electronic building blocks of all carbon allotropes and compounds the sp and the sp orbitals. 

---