Diatomic molecules, atomization metals

The terms AHAm and AHAy are the enthalpies of atomization of the metal and the nonmetal, respectively. For gaseous diatomic nonmetals, AHA is the enthalpy of dissociation (bond energy plus RT) of the diatomic molecule. For metals which vaporize to form monatomic gases, AHA is identical to the enthalpy of sublimation. If sublimation occurs to a diatomic molecule, M2> then the dissociation enthalpy of the reaction must also he included ... 

The formulae apply to the (111) surface of an f.c.c. metal. E M — M) and E A — A) are the bond strengths of diatomic molecules of metal atoms and adsorbing atoms respectively and X f and their respective chemical affinities. i/ is the metal atomic valency. Since t/ < I2y according to both formulae the chemisorptive bond strength is smaller than that of the corresponding free surface molecule. It is revealing to understand the physical basis of Eqs.(3.6). Equation (3.6a) is valid in the surface molecule limit. It ignores Equation (3.6b) applies in the weak... 

Aromatics, alkylation of, 10, 165 Atomization, of diatomic molecules, by metals, 15, I... 

In contrast to molecular adsorption, the interaction energy of atoms as C, O, or N with a metal surface is a strong function of coordination number. Adsorbed atoms almost always prefer bonding in sites of threefold or fourfold coordination. Molecules can also adsorb on top or bridge sites. As will be seen, this has major consequences for the dissociation paths of diatomic molecules on metal surfaces. 

It is this resonance energy that would be in the main responsible for the difference in energy of the crystal and the gas of diatomic molecules Li2. But the heat of formation of Li2 molecules from atoms is only 6-6 kcal./g.-atom, whereas that of the metal is 39kcal./g.-atom. It seems unlikely, by comparison for example with the analogous case of Kekule-like resonance in aromatic molecules, that the great difference, 32-4 kcal./g.-atom, could result from the synchronized resonance, of type f Li—Li Li Li)... 

To describe the band structure of metals, we use the approach employed above to describe the bonding in molecules. First, we consider a chain of two atoms. The result is the same as that obtained for a homonuclear diatomic molecule we find two energy levels, the lower one bonding and the upper one antibonding. Upon adding additional atoms, we obtain an additional energy level per added electron, until a continuous band arises (Fig. 6.9). To describe the electron band of a metal in a... 

The experiments with a beam of silver particles were conducted at room temperature. The energy of dissociation of diatomic molecules of silver is 1.78 eV, the heat of evaporation of silver molecules is 95 kcal/mol [46], and the heat of evaporation of an uniatomic silver is 64 kcal/mol. Mass-spectrometric studies [46] of silver vapour above a metallic silver showed that the ratio of number densities of ions Ag /Ag2 is equal to two. In other studies [47], a considerably larger value of this ratio was found. At 1037 - 1147 C molecular mass of silver particles in vapours was found to be 278 90 [46], i.e., an average number of atoms in a molecule of silver is 2.56. 

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