Diamond, Graphite, Graphene, Bucky Ball and Nanotube (Fun with Carbon) (original) (raw)

2011, Chemicals for Life and Living

Diamond is the hardest material, and that suggests sturdiness and long-lastingness. Yet amazingly, it is simply made of carbon atoms only. Coal is almost pure carbon. Graphite, an allotrope of carbon, is a better example in contrast to diamond because graphite is also pure carbon. Graphite is the material used in pencils among others. Diamond and graphite could not be more different. One is transparent, colorless and hard while the other is completely black and relatively soft. Diamond is much denser (density = 3.51 g/cm 3) than graphite (2.25 g/cm 3). Diamond is an electrical insulator, while graphite works like a metal, an electric conductor. Why are they so different, if made of the same carbon atoms and carbon atoms only? To understand this difference we have to start with some basic ideas about the chemical bonds involving carbon atoms. Carbon, C, is the sixth element in the periodic chart, and has six electrons (1s 2 2s 2 2p 2 electronic configuration). Four of these electrons (in 2s and 2p orbitals) are the so-called valence electrons and are involved in bonding. [The two electrons in 1s orbital are so tightly held by the positively charged nucleus that it is hard to move them around; they are called "core electrons" and are not involved in bonding and chemical reactions]. As we discuss in the appendix (Chap. 19), a bonding between two atoms is made by a pair of electrons which is shared by those two atoms. Let us suppose that the type of bonding we are dealing with here forms when two atoms each contribute one electron to their bonding; this type of bonding is called "covalent bonding." Now carbon can bind as many as four atoms about it, as it has four valence electrons available. One of the simplest such compounds is methane, CH 4 , the major component of natural gas. The carbon atom is bound with four hydrogen atoms as shown below (Fig. 11.2). This shape is called "tetrahedral," because it forms a tetrahedron if adjacent hydrogen atoms are connected by imaginary lines (not "bond"). The connection, i.e., the bond between C and H (we simply express it as C-H), is made of two 11 Diamond, Graphite, Graphene, Bucky Ball and Nanotube (Fun with Carbon)