Carbon diatomic molecule, orbitals

Of these three diatomic moiecuies, only N2 exists under normal conditions. Boron and carbon form soiid networks rather than isolated diatomic molecules. However, molecular orbital theory predicts that B2 and C2 are stable molecules under the right conditions, and in fact both molecules can be generated in the gas phase by vaporizing solid boron or soiid carbon in the form of graphite. 

The bond orbitals for graphite can accommodate three electrons per carbon atom. The remaining electrons go into p states oriented perpendicular to the plane in Fig. 3-10 and are analogous to the a states of diatomic molecules, as discussed in Chapter 1. The tc states are coupled by small matrix elements and broaden into a rather narrow band. There are enough electrons to half-fill this band (because of the two spin states). By filling only the lower half of the band these electrons... 

In many cases the molecular orbitals for a heteronuclear diatomic molecule may be worked out in a straightforward manner as for hydrogen chloride. In others, however, certain difficulties arise and we shall take as an example the case of carbon monoxide, the structure of which has been the subject of much controversy. In carbon monoxide, as in the nitrogen molecule, there are fourteen valency electrons and Mullikan has formulated the structure of both molecules as... 

Carbon monoxide. Carbon monoxide is one of the most commonly used probe molecules in the study of the chemical properties of metal surfaces. CO represents a step in the direction of complexity compared to atomic adsorbates and diatomic molecules. On one hand, the bonding involves molecular orbitals and it is sensitive to the detailed electronic structure of the metal surface. This allows one to use the CO bonding properties as a probe of changes in surface electronic structure. Yet at the same time, in many cases CO retains aspects of the simplicity that atomic adsorbates have. 

The molecular orbital model as a linear combination of atomic orbitals introduced in Chapter 4 was extended in Chapter 6 to diatomic molecules and in Chapter 7 to small polyatomic molecules where advantage was taken of symmetry considerations. At the end of Chapter 7, a brief outline was presented of how to proceed quantitatively to apply the theory to any molecule, based on the variational principle and the solution of a secular determinant. In Chapter 9, this basic procedure was applied to molecules whose geometries allow their classification as conjugated tt systems. We now proceed to three additional types of systems, briefly developing firm qualitative or semiquantitative conclusions, once more strongly related to geometric considerations. They are the recently discovered spheroidal carbon cluster molecule, Cgo (ref. 137), the octahedral complexes of transition metals, and the broad class of metals and semi-metals. 

When carbon vaporizes at extremely high temperatures, among the species present in the vapor is the diatomic molecule C2. Write a Lewis formula for C2. Does your Lewis formula of C2 obey the octet rule (C2 does not contain a quadruple bond.) Does C2 contain a single, a double, or a triple bond Is it paramagnetic or diamagnetic Show how molecular orbital theory can be used to predict the answers to questions left unanswered by valence bond theory. 

Your molecular orbital diagram should look like figure 2.18 which shows the MO diagram for Period 2 homonuclear diatomic molecules from Li2 to N2. Each carbon atom has four valence electrons, thus a total of 8 electrons has to be placed in the molecular orbitals on the diagram. Keep in mind that you still follow the Hund s rule and the Pauling exclusion principle when filling molecular orbitals with electrons. See the solution for E2.22... 

A key question is whether the diatomic molecule in its interaction with metal surfaces remains molecular or dissociates into carbon and oxygen. Broden et al. (3) predicted, by the perturbation of molecular orbitals for CO adsorbed, that only iron could dissociate CO. However, other metals in Group VIII such as nickel (A) ruthenium (5) and rhodium (6) can dissociate CO. Recently Ichikawa et al.(7) observed that disproportionation of CO to CO2 and carbon occurs on small particles of silica-supported palladium. These results show that carbon deposition phenomena may occur via either dissociation of CO on the metals used or disproportionation of CO to CO and carbon on small platinum particles. Cant and Angove (8) studied the apparent deactivation of Pt/Si02 catalyst for the oxidation of carbon monoxide and they suggested that adsorbed CO forms patches and that oxygen atoms are gradually consumed. 

LDOS of carbon orbitals in gas phase C, in Rh-C diatomic molecule and carbon adsorbed onefold and twofold on -w / , Rh(lll). 

D) Interactions of carbon with metal d, (group) orbitals in Rh-C diatomic molecule (1) C adsorbed onefold (2) C adsorbed twofold (3)... 

The second-row elements including carbon, oxygen and nitrogen involve p atomic orbitals as well as 2s orbitals. An example of a heteronuclear diatomic molecule involving these elements is carbon monoxide, C=0. The carbon monoxide molecule has 14 electrons, and the orbitals for each atom are Is, 2s, 2p, and... 

Figure 3.6 shows the LCAO method for generating molecular orbitals of diatomic molecules such as H2. In real molecules, the atomic orbitals of elemental carbon are not really transformed into the molecular orbitals found in methane (CH4). Figure 3.6 represents a mathematical model that mixes atomic orbitals to predict molecular orbitals. Molecular orbitals exist in real molecules and the LCAO model attempts to use known atomic orbitals for atoms to predict the orbitals in the molecule. Molecular orbitals and atomic orbitals are very different in shape and energy, so it is not surprising that the model used for diatomic hydrogen fails for molecules containing other than s-orbitals. 

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