Oxides lattice energies, table

Some properties of selected vanadium compounds are Hsted in Table 1. Detailed solubiUty data are available (3), as are physical constants of other vanadium compounds (4). Included are the lattice energy of several metavanadates and the magnetic susceptibiUty of vanadium bromides, chlorides, fluorides, oxides, and sulfides (5). 

The MEG model has been extensively used to determine lattice energies and interionic equilibrium distances in ionic solids (oxides, hydroxides, and fluorides Mackrodt and Stewart, 1979 Tossell, 1981) and defect formation energies (Mack-rodt and Stewart, 1979). Table 1.21 compares the lattice energies and cell edges of various oxides obtained by MEG treatment with experimental values. 

Table 1.21 MEG values of lattice energy and lattice parameter for varions oxides, compared with experimental values. Source of data Mackrod and Stewart (1979). C/ is expressed in kJ/mole (in A) corresponds to the cell edge for cnbic snbstances, whereas it is the lattice parameter in the a plane for AI2O3, Fe203, and Ga203 and it is the lattice parameter parallel to the sixfold axis of the hexagonal unit cell in mtiles CaTi03 and BaTi03.

Compounds of aluminium and magnesium in the lower oxidation states, A1(I) and Mg (I), do not exist under normal conditions. If we make an assumption that the radius of AF or Mg is the same as that of Na (same row of the Periodic Table), then we can also equate the lattice energies, MCI. Use this information in a Born-Haber cycle to calculate... 

Table 5.5 Experimental lattice energies for some oxides, comparing calculated (Kapustinskii) and experimental ratios for different oxidation states of elements (all lattice energies in kJ mol )...

Many elements exhibit several different oxidation states, and the relative stabilities of MX and MX are often more difficult to assess. Assuming the lattice energy to be inversely proportional to the shortest M-X distance in the structure, then, since halide ion radii increase from F to I (Table 1), fluorides generally have the largest values and iodides the smallest values for lattice energies. However, one has to consider the stabilities of fluorides or iodides with respect to each other, for example, a solid salt MX +i decomposing into another, MX , and 1/2X2. From the Bom-Haber cycle (with some approximations) one obtains for such a reaction... 

Table 3.12. Calculated lattice energies (WJ and lattice parameters ( ) obtained for a range of metal oxides using the modified electron-gas approach, compared with experimental values...

Table CL VI11. Lattice Energies of Aletallic Oxides in kcals...

Given that strontium oxide crystallizes with the same structure as calcium oxide, use data tables to estimate the minimum cation/anion distance and hence determine the lattice energy for SrO. 

There are four different ways in which non-stoichiometric compounds can form from a compound AB, as given in Table 6.1. These are oxidation and reduction of the metal cation, introduction of vacancies or introduction of interstitials. Most examples are in the category where the metal is oxidized and more anions are added. The formation of more bonds produces an increase in the lattice energy, which compensates for the energy required to form the defect... 

Table 6 Lattice energy, melting temperature, thermal expansion, and modulus for alkaline earth oxides with the rock salt structure...

TABLE 9.1 Lattice Energies and Melting Points of Some Alkali Metal and Alkaline Earth Metal Halides and Oxides... 

Table 3.05. Lattice energies of some oxides and sulphides Values are in kcal/mole...

Figure 11.5 shows the trend in melting points of the oxides MgO, CaO, SrO and BaO crystallize with an NaCl lattice and the decrease in melting point reflects the decrease in lattice energy as the cation size increases (Table 11.1). The high melting point of MgO makes it suitable as a refractory material (see Box 11.6). 

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