Hybrid covalent energy table

Consider hexagonal boron nitride, shown in Fig. 3-10. Define a hybrid covalent and hybrid polar energy for this structure, in analogy with the corresponding definitions for tetrahedral solids in Eqs. (3-4) and (3-6). Compare the polarity obtained from these values with that of tetrahedral BN, listed in Table 7-2. Take d = 1.42 A as in graphite. Notice that many values arc modified by having sp hybrids rather than sp hybrids. 

Bond orbitals are constructed from sp hybrids for the simple covalent tetrahedral structure energies are written in terms of a covalent energy V2 and a polar energy V3. There are matrix elements between bond orbitals that broaden the electron levels into bands. In a preliminary study of the bands for perfeet crystals, the energies for all bands at k = 0 are written in terms of matrix elements from the Solid State Table. For calculation of other properties, a Bond Orbital Approximation eliminates the need to find the bands themselves and permits the description of bonds in imperfect and noncrystalline solids. Frrors in the Bond Orbital Approximation can be corrected by using perturbation theory to construet extended bond orbitals. Two major trends in covalent bonds over the periodic table, polarity and metallicity, are both defined in terms of parameters from the Solid State Table. This representation of the electronic structure extends to covalent planar and filamentary structures. 

In making a covalent bond between carbon and chlorine from the 2px orbital on carbon and the 3px orbital on chlorine, we have an interaction (Fig. 1.45) between orbitals of unequal energy (-10.7 eV for C and -13.7 eV for Cl, from Table 1.1). The interaction diagram could equally have been drawn using sp3 hybrids on... 

The formation of the same iron-oxygen covalent bonds from either (1) oxidized iron plus oxy anions via electron-transfer (redox) reactions or (2) radical-radical coupling reactions is summarized in Table 3-11. The valence-electron hybridization for the iron center is included as well as the spin state and estimated covalent bond-formation free energy (AGbf)- A similar set of reactions and data for iron-porphyrin compounds is presented in Table 3-12. Section a emphasizes that, just as the combination of a proton with a hydroxide ion yields a covalent H-OH bond (Table 3-11), (1) the combination of protons and porphyrin dianion (Por -) yields covalent porphine (H2Por), and (2) the addition of Lewis acids (Zn2+ or Fe2+) to porphine (H Por) oxidatively displaces protons to give covalent-bonded ZnilPor and Fe iPor. 

Studies of the spectra of Group I metal vapors at about the boiling points of the metals show the presence of 1 % of diatomic molecules whose dissociation energies decrease with increasing atomic number (Table 6.1). These molecules provide the most unambiguous cases of covalent bonding of the alkalis some s-p hybridization is considered to be involved. 

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