Predictions using lattice energy

Thallium has two stable oxidation states, + f and +3. Use the Kapustmskii equation to predict the lattice energies of TIF and TIF. Predict the enthalpies of formation of these compounds. Discuss. 

The use of Eq. 4.13 to predict the lattice energy of an ionic compound may be illustrated as follows. For sodium chloride the various factors are... 

Even though ionic model calculations do not always give accurate predictions of lattice energies (and especially when the approximate Kapustinskii equation is used) the trends predicted are usually reliable and can be used to rationalize many observations in inorganic chemistry. 

Models have also been developed which predict periodic structures by using lattice energy minimization and vibrational spectra using lattice dynamics. In this case the proper determination of potential functions used to describe the interactions between atoms is critical for canying out adequate predictions. Very recently a very powerful shell model ion-pair potential for aluminosilicates has been derived by fitting its parameters to data obtained from quantum-chemical calculations on molecular models that represent typical subunits of zeolites [8j. The correct use of such potential describes accurately the long-range... 

It is also interesting to note that metal ions having low polarizability (Al3+ Be2+ etc.) are those that are acidic (as shown in Eq. (9.17)). Also, in Chapter 7 we discussed how the polarization of ions leads to a lattice energy that is higher than that predicted on the basis of electrostatic interactions alone. The polarizability data shown in the table make it easy to see that certain ions are much more polarizable than others. Although we will not visit again all of the ramifications of electronic polarizability, it is a very useful and important property of molecules and ions that relates to both chemical and physical behavior. 

The extent of the ionization produced by a Lewis acid is dependent on the nature of the more inert solvent component as well as on the Lewis acid. A trityl bromide-stannic bromide complex of one to one stoichiometry exists in the form of orange-red crystals, obviously ionic. But as is. always the case with crystalline substances, lattice energy is a very important factor in determining the stability and no quantitative predictions can be made about the behaviour of the same substance in solution. Thus the trityl bromide-stannic bromide system dilute in benzene solution seems to consist largely of free trityl bromide, free stannic bromide, and only a small amount of ion pairs.187 There is not even any very considerable fraction of covalent tfityl bromide-stannic bromide complex in solution. The extent of ion pair and ion formation roughly parallels the dielectric constant of the solvents used (Table V). The more polar solvent either provides a... 

Mass spectrometric measurements coupled with solution thermochemical results are the sources of solvation enthalpy values for anions and cations. These data are related to the lattice energy, which is a parameter used to assess the ionic character of solids and predict their standard enthalpies of formation. An introduction to that... 

Most ot the enthalpies associated with steps in the cycle can be estimated, to a greater or less accuracy, by experimental methods. The lattice energy, however, is almost always obtained theoretically rather than from experimental measurement. It might be supposed that the "enthalpy of dissociation of a lattice coukl be measured in the same way as the enthalpy of atomization of the metal and nonmctal, that is, by heating the crystal and determining how much energy is necessary to dissociate it into ions. Unfortunately, this is experimentally very difficult When a crystal sublimes (AHj), the result is not isolated gaseous ions but ion pairs and other clusters. For this reason it is necessary to use Eq. 4.13 or some more accurate version of It. Wc can then use the Bom-Haber cycle to check the accuracy of our predictions if we can obtain accurate data on every other step in the cycle Values computed from the Bom-Haber cycle are compared with those predicted by Eq. 4.13 and its modifications in Table 4.3. 

The enthalpy of formation of an ionic compound can be calculated with an accuracy of a few percent by means of the Born-Land6 equation (Eq. 4.13) and the Bcrn-Haber cycle. Consider NaCI. for example. We have seen that by using the predicted internuclear distance of 283 pm (or the experimental value of 281.4 pm), the Madelung constant of 1.748, the Rorn exponent, n, and various constants, a value of — 755 kJ mol-1 could be calculated for the lattice energy. The heat capacity correction is 2.1 kJ mol-1, which yields U 9i = —757 kJ mol-1. The Bom-Haber summation is then... 

Using any necessary data from appropriate sources, predict the enthalpy of formation of KCI by means of a Bom-Haber cycle. You can check your lattice energy against Table 4.3. 

Computer simulation using lattice models and energy landscape theory using abstract models predict that the fastest folding of small proteins should occur without intermediates and by an extended nucleation process. Stable intermediates slow... 

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