handbook of carbon, graphite, diamond and fullerenes

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The Element Carbon 15 The configuration of the carbon atom described above refers to the configuration in its ground state, that is, the state where its electrons are in their minimum orbits, as close to the nucleus as they can be, with their lowest energy level. K Shell Electrons 1S Nucleus 6 Protons 6 Neutrons (Carbon-12) 2s 11 K Shell L Shell L Shell Electrons 2Px 1 Tv 2F 2Py 1 IO half-fil orbitals ed 2p2 Note: Arrow indicates direction of electron spin Figure 2.1. Schematic of the electronic structure of the carbon atom in the ground state. Valence Electrons and lonization Potential. In any given atom, the electrons located in the outer orbital are the only ones available for bonding to other atoms. These electrons are called the valence electrons. In the
16 Carbon, Graphite, Diamond, and Fullerenes case of the carbon atom, the valence electrons are the two 2p orbitals. Carbon in this state would then be divalent, since only these two electrons are available for bonding. Divalent carbon does indeed exist and is found in some highly reactive transient-organic intermediates such as the carbenes (for instance methylene). However, the carbon allotropes and the stable carbon compounds are not divalent but tetravalent, which means that four valence electrons are present. 16 ' Howthis increase in valence electrons occurs is reviewed in Sec. 3.0. The carbon valence electrons are relatively easily removed from the carbon atom. This occurs when an electric potential is applied which accelerates the valence electron to a level of kinetic energy (and corresponding momentum) which is enough to offset the binding energy of this electron to the atom. When this happens, the carbon atom becomes ionized forming a positive ion (cation). The measure of this binding energy is the ionization potential, the first ionization potential being the energy necessary to remove the first outer electron, the second ionization potential, the second outer second electron, etc. The ionization energy is the product of the elementary charge (expressed in volts) and the ionization potential, expressed in electron volts, eV (one eV being the unit of energy accumulated by a particle with one unit of electrical charge while passing though a potential difference of one volt). The first ionization potentials of carbon and other atoms close to carbon in the Periodic Table are listed in Table 2.2. It should be noted that the ionization energy gradually (but not evenly) increases going from the first element of a given shell to the last. For instance, the value for lithium is 5.39 V and for neon, 21.56 V. It is difficult to ionize an atom with a complete shell such as neon, but easy to ionize one with a single-electron shell such as lithium. As shown in Table 2.2 above, carbon is located half-way between the two noble gases, helium and neon. When forming a compound, carbon can either lose electrons and move toward the helium configuration (which it does when reacting with oxygen to form CO2), or it can gain electrons and move toward the neon configuration (which it does when combining with other carbon atoms to form diamond). The six ionization potentials of the carbon atom are shown in Table 2.3.
Page 1 and 2: HANDBOOK OF CARBON, GRAPHITE, DIAMO
Page 3 and 4: Contents 1 Introduction and General
Page 5 and 6: xii Contents 5.0 ELECTRICAL PROPERT
Page 7 and 8: xiv Contents 2.0 THE CVD OF PYROLYT
Page 9 and 10: xvi Contents 6.0 CERAMIC-MATRIX, CA
Page 11 and 12: xviii Contents 4.0 NATURAL AND HIGH
Page 13 and 14: xx Contents 2.0 STRUCTURE OF THE FU
Page 15 and 16: Preface ix technology, processes, e
Page 17 and 18: 2 Carbon, Graphite, Diamond, and Fu
Page 25 and 26: 10 Carbon, Graphite, Diamond, and F
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66 Carbon, Graphite, Diamond, and F
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Synthetic Carbon and Graphite: Carb
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Vitreous Carbon 1.0 GENERAL CONSIDE
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8 Carbon Fibers 1.0 GENERAL CONSIDE
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Applications of Carbon Fibers 1.0 C
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10 Natural Graphite, Graphite Powde
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11 Structure and Properties of Diam
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12 Natural and High-Pressure Synthe
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13 CVD Diamond 1.0 INTRODUCTION The
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15 The Fullerene Molecules 1.0 GENE
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Glossary Ablation: The removal of m
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Index Ablation 38 Absorption bands
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Copyright © 1993 by Noyes Publicat
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vi Series HANDBOOK OF CHEMICAL VAPO
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