Enthalpy change group 18 elements

The reduction potentials of the Group 1 elements are calculated from equation (6.8) by dividing the enthalpy change by -F. The results are given in Table 6.6. 

The group 18 elements are the noble gases (see Chapter 17), and Table 5.1 lists selected physical data for these elements. Each element (with the exception of helium, see footnote in Table 5.1) solidifies only at low temperatures. The enthalpy changes accompanying the fusion processes are very small, consistent with the fact that only weak van der Waals forces operate between the atoms in the solid state. In the crystalline solid, ccp structures are adopted by each of solid Ne, Ar, Kr and Xe. 

Theoretically this kj -value is again given by an electronic matrix element and a Franck-Condon factor. Systems with the same free enthalpy change should have the similar Franck-Condon factors, since the latter is a function of the former. However, the yields are scattered, which should be reduced to the difference of the electronic matrix elements. Small yields were observed for the systems with a component molecule having carbonyl group or heteroatom. In these molecules, an n-Tr triplet level is placed between or near the initial electron transfer and the final triplet states, which may accelerate the intersystem crossing. The kj -values increase and the formation yield of ion radicals is reduced. This interpretation is consistent with the result that the yield is determined by the chemical properties of the component molecules. 

Typical elements in Groups V. VI and VII would be expected to achieve a noble gas configuration more easily by gaining electrons rather than losing them. Electron affinity is a measure of the energy change when an atom accepts an extra electron. It is difficult to measure directly and this has only been achieved in a few cases more often it is obtained from enthalpy cycle calculations (p. 74). 

The calculated Coulomb parts of the fi ee energy change of some hydrolysis and the complex formation reactions, Eqs. (33-35), are given in Table 13 [219]. The results have shown that the electronic structures, as well as formation enthalpies of the Rf complexes are very similar to those of the Hf and Zr complexes, thus explaining the similarity in the chemical behaviour between Zr and Hf on the one hand, and Rf on the other hand, observed in the first solvent extraction experiments with the group-4 elements including Rf [213]. 

Although there is no change of order in the values of the enthalpies of atomization of the Group 15 elements, the value for phosphorus seems unusually low. This is probably because of the inherent weakness of the bonding in the tetrahedra, associated with the very unusual 60 bond angles. 

Pershina, V., Fricke, B. Electronic structure and properties of the group 4, 5, and 6 highest chlorides including elements 104, 105, and 106. J. Phys. Chem. 98, 6468-6473 (1994) Ionova, G.V., Pershina, V.G., Suraeva, I.I., Suraeva, N.I. Estimation of change of thermodynamic properties of transactinoid series metals sublimation enthalpy. Radiokhimiya 37, 307-316 (1995)... 

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