Valence energy diagram

To date there is no evidence that sodium forms any chloride other than NaCl indeed the electronic theory of valency predicts that Na" and CU, with their noble gas configurations, are likely to be the most stable ionic species. However, since some noble gas atoms can lose electrons to form cations (p. 354) we cannot rely fully on this theory. We therefore need to examine the evidence provided by energetic data. Let us consider the formation of a number of possible ionic compounds and first, the formation of sodium dichloride , NaCl2. The energy diagram for the formation of this hypothetical compound follows the pattern of that for NaCl but an additional endothermic step is added for the second ionisation energy of sodium. The lattice energy is calculated on the assumption that the compound is ionic and that Na is comparable in size with Mg ". The data are summarised below (standard enthalpies in kJ) ... 

Fig. 1. Band-edge energy diagram where the energy of electrons is higher in the conduction band than in the valence band (a) an undoped semiconductor having a thermally excited carrier (b) n-ty e doped semiconductor having shallow donors and (c) a -type doped semiconductor having shallow acceptors.

FIGURE 2.7. (a) Three active pz orbitals that are used in the quantum treatment of the X + CH3-Y— X-CH3 + Y Sw2 reaction, (b) Valence-bond diagrams for the six possible valence-bond states for four electrons in three active orbitals, (c) Relative approximate energy levels of the valence-bond states in the gas phase (see Table 2.4 for the estimation of these energies). 

Figure 3.28 A schematic energy diagram for valence MOs of homonuclear diatomic molecules (following Mulliken). The order of 02P and 7t2p MOs should be reversed for 14 or fewer electrons.

Figure 7.9 Potential energy diagram for electrons in and near a metal to which a high negative potential is applied. Electrons in the valence band of the metal see an attractive potential equal to -eFr (F is the applied field in V/cm) outside the metal behind a barrier formed by the applied field and the image potential.

The donor electron level, cd, which may be derived in the same way that the orbital electron level in atoms is derived, is usually located close to the conduction band edge level, ec, in the band gap (ec - Ed = 0.041 eV for P in Si). Similarly, the acceptor level, Ea, is located close to the valence band edge level, ev, in the band gap (ea - Ev = 0.057 eV for B in Si). Figure 2-15 shows the energy diagram for donor and acceptor levels in semiconductors. The localized electron levels dose to the band edge may be called shallow levels, while the localized electron levels away from the band edges, assodated for instance with lattice defects, are called deep levels. Since the donor and acceptor levels are localized at impurity atoms and lattice defects, electrons and holes captured in these levels are not allowed to move in the crystal unless they are freed from these initial levels into the conduction and valence bands. 

Fig. 10-3. Energy diagrams for an n-type semiconductor electrode (a) in the daik and (b) in a photoexdted state S = aqueous solution = conduction band edge level at an interface cy = valence band edge level at an interface = Fermi level of oxygen...

Fig. 14 (a) Equilibrium energy diagram for a pn junction in an inorganic semiconductor material with intrinsic Fermi energy Ep , conduction band energy E, valence band energy The quantity Vu... 

Fig. 118a. Schematic of the electron injection process at a highly porous H02 electrode surface (only a patchy and fractured pyrite layer can be expected on the highly porous Ti02 layer), b Surface TiOj/FeSj energy diagram at pH = 1, indicating the injection of electrons from the valence band of FeS2 into the conduction band of HO2, and the reaction of holes with the redox system [714]...

Fig. 34. Schematic valence band diagram of resonant tunneling diode structures, simplified diagram of energy versus wave vector parallel to the interface, and resulting /-V curve by spin-splitting of the valence band of...

Fig. 13.13 Poienual energy diagram for a photochemicaDy induced homonudeor electron transfer in a mixed valence complex (R = reactants ...

Figure 4.68 Energy diagram of the valence and conduction bands of a semiconductor-electrolyte interface. The bending of the bands corresponds to the effect of the electric field...

Isomerization of the retinal Schiff s base can occur when the molecule is excited with light, because the C-l 1-C-12 bond loses much of its double-bond character in the excited state. The valence bond diagrams of figure S2.7 illustrate this point. In the ground state of rhodopsin, the potential energy barrier to rotation about the C-l 1-C-l2 bond is on the order of 30 kcal/mol. This barrier essentially vanishes in the excited state. In fact, the energy of the excited molecule probably is minimal when the C-11 -C-l2 bond is twisted by about 90° (fig. S2.8). The excited molecule oscillates briefly about this intermediate conformation, and when it decays back to a ground state it usually settles into the ail-trans isomer, bathorhodopsin. 

In figure 11.1.8 you can see an energy diagram with in it a valence electron in the d-orbital of a random metal ion from one of... 

In a sodium atom, the 3s valence electrons of the atoms will collide. Due to this the valence electrons of the individual atoms will not all possess the same energy, yet at the same time differ little in energy. As a result various, closely spaced 3s levels will occur in the energy diagram, which together form the so-called valence band (fig. 11.4.3)... 

In an insulator the electrons are closely bound to the atoms or ions. They can only be persuaded to move, i.e. they will only move from the valence band to the conduction band, when relatively much energy is provided. The energy diagram of these materials is represented in figure 11.4.4. 

Figure 11.7 Potential energy diagrams for a two-component mixed valence device with (a) negligible, (b) weak and (c) strong electronic coupling. The dashed curves represent unperturbed zero-order states. The horizontal axis represents generalised nuclear coordinates, including contributions from both ligand atom positions and solvent sphere.

Figure 6. Potential energy diagram for[M /Mo(CN) y mixed-valence compounds. Mn+/Mo w Precursor complex M(n-l)/Mov Successor complex E0p Energy of the optical IT...

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