Metal sublimation enthalpies

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)... 

On descending the sub-group the colour generally becomes lighter, indicating an increased separation between the frontier orbitals, which are believed to be predominantly associated with the metal frame, and therefore a decrease of the metallic character. The overall constancy of the values of the enthalpies of formation of these compounds, and the use of an estimated sublimation enthalpy of ca. 

The relative difference between the dissociation enthalpy of two-atomic elemental molecules given by Gurevic [64] and the sublimation enthalpy of these elements [65] from Method 1 can be used to estimate the metallic character (m) of elements (Method 10) [28], see Figure 9 ... 

The net adsorption enthalpies and the predicted sublimation enthalpies (see Method 1) were used to calculate the adsorption enthalpies of transactinides on selected metal surfaces (Method 11). The metals, which are presented in Table 4, can be used as stationary phase in gas adsorption chromatographic experiments for selective gas chemical separations or, in the case of high adsorption interaction, as strong fixation materials for the sample preparation in the measurement of transactinides. 

The stabilities of the Eu2+, Yb2+, and Sm2+ ions correlate with the third ionization enthalpies of the atoms and the sublimation enthalpies of the metals. The Eu2+(aq) ion is readily obtained by reducing Eu3+(aq) with Zn or Mg, while preparation of the others requires use of Na/Hg or electrolysis. The aqueous Eu2+ solutions are easily handled, but those of Sm2+ and Yb2+ are rapidly oxidized by air and by water itself. The Ln2+ ions show many resemblences to Ba2+, giving insoluble sulfates, for example, but soluble hydroxides. Europium can be easily separated from other lanthanides by Zn reduction followed by precipitation of the other Ln3+ hydroxides. 

With a typical value of the sublimation enthalpy of metals, Asubff = 150 kj mol the detachment enthalpy (work of separation) per atom in a kink position is calculated to be ink = 250 X 10 J and the binding energy of two next neighbor atoms to be y/i = 41.7 X 10 J per atom. With that value of y/ every 75th atom on a step would be in a kink position at room temperatures. 

The first step is to sublimate the lithium metal into lithium gas. The sublimation enthalpy is 161 kJ/mole. Thus 161 kJ are required. 

Anomalous structures (e.g. bcc gold, fee lithium) have sometimes been found these seem to occur most frequently with metals of low sublimation enthalpy, and less often with palladium and platinum. Their formation may be linked to an epitaxial effect of the support on which they are formed and grow. Clearly developed crystal planes were only shown by particles larger than about 2 nm ° Mdssbauer spectroscopy showed a platinum particle with 309 atoms to have the normal fee structure,but palladium-platinum particles suffered electron-beam-induced change from fee to cph. ... 

Values of the sublimation enthalpy of main group and transition metals are shown in Table 2.3 2... 

Sublimation enthalpies, energies of atoms in ideal kink positions and bond energies between the two nearest atoms, main group and transition metals ... 

The values given by Miedema are the formation enthalpies of solid solutions of A in B or vice versa. The solved metal is embedded into the matrix of the solvent. Using a Haber-Born cycle as shown in Figure 2.39 the sublimation enthalpy of the solved metal embedded in the matrix of the solvent can be calculated. Results of sublimation enthalpies of the solved metal embedded in the matrix of the solvent are shown in Table 2.4b. 

Sublimation enthalpies calculated with the Bom-Haber cycle in Figure 2.39 for transition metals A in B... 

Bond energies calculated from the sublimation enthalpies for alloys of transition metals... 

The experimentally determined Afla° values, measured with trace amounts (at zero surface coverage), can be correlated with their macroscopic sublimation enthalpies AH (Turler et al. 1999). From an empirically derived linear correlation between AH and AH, the sublimation enthalpy of Sg02Cl2 can be estimated as 127 kJ/moL This is an important quantity to estimate the sublimation enthalpy of Sg metal. Seaborgium is estimated to have an equal or even higher sublimation enthalpy than W, the least volatile element in the periodic table (Turler et al. 1999). 

Fig. 1. Enthalpies of sublimation of rare earth and actinide metals and enthalpies of formation of their 3 + aquo-ions. Values of As bi/f for Md-Lr and A,// [Es " (aq)-Lr (aq)] are estimates.

Atomic Number Atomic Mass Density (g cm ) Melting Point Boiling Point Metallic Radius Enthalpy of Sublimation at 25°C... 

The dissociation energies of the homonuclear diatomic molecules, D (R2), were calculated from the mass spectrometrically measured ion currents and the thermal functions evaluated for the gaseous species. The error limits shown in table 1 are upper limits and include those due to experimental uncertainties and also those due to the uncertainties in calculated thermal functions. The Do(R2) values (last column, table 1) also show the double periodicity exhibited by the sublimation enthalpies. This double periodicity comes about because (1) in the thermodynamic calculations the of th rare-earth metals is needed,... 

The highest correlation coefficient (0.98) is for enthalpy of vaporization and standard enthalpy of atomization. For metals, the latter one is actually the standard sublimation enthalpy and is given, according to Hess law, by the sum of the standard enthalpies of fusion and vaporization. The enthalpies of vaporization are those at the boiling temperature and, therefore, lower than the standard ones. Other very close correlations are those between the boiling... 

The above-mentioned procedure is also useful with respect to the description of new relationships for series of similar compoimds. Some special features of changes in the sublimation enthalpy over series of such compoimds are well seen in the dependence of Asub °(298) on the position of the 4f metal in the lanthanide series. A decrease in the coordination number (CN) of a 4f metal in the crystal lattice of the corresponding compound leads to a lower Asubff°29s value. This is observed in going from P-YF3- to LaF3-t) e structures of the trifluorides. A similar phenomenon is characteristic for the lanthanide trichlorides and dichlorides. Moreover, the absolute value of the sublimation enthalpy reflects the stability of the compound and its resistance to thermal actions. As expected, such correlations are t) ical for other series of similar 4f compounds. 

One general rule of trends in the Periodic Table is that the metallic character of all elements increases with increasing atomic number Z along the groups of s-ele-ments and of p-elements. The relative difference between the dissociation enthalpy of two-atomic molecules, and the sublimation enthalpy, of these... 

Figure 39 depicts the trend of sublimation enthalpies within elements of group 12. The experimental result of Cn nicely supports the classical expectation, already predicted in 1976 by Eichler [125]. Hence, from the experimental study it follows that Cn is a very volatile noble metal which still exhibits a metallic character. 

Chemistry of the Heaviest Elements ) sufficiently accurate, predict —A// (F1) = 68 kJ mol somewhat less volatile than Cn [146]. It was argued, that on transition metal surfaces FI should adsorb stronger than Cn, due to chemical forces since the 7pi/2(Fl) atomic orbital is less stabilized than the 7i(Cn) atomic orbital. On the other hand, relativistic solid-state calculation yield cohesive energies (equivalent to sublimation enthalpies) which are higher for Cn (1.1 eV [138]) compared to FI (0.5 eV [147]). This prediction is at variance with the calculation from [146] under the assumption that sublimation enthalpies correlate with the adsorption enthalpies on Au surfaces see Fig. 38. 

From these measured properties, thermodynamic state functions (enthalpies of sublimation, entropies, and free-energy functions) have been derived. For several actinides, these properties have been critically reviewed by Hultgren et al. [24] and more recently by Getting, Rand, and Ackermann [14]. The latter compilation includes properties for the metallic state and for ideal gas to 5(XX) K for the elements Th through Cm. Sublimation enthalpies (determined from measured vaporization behavior for Th through Es) and standard entropies (determined from measured heat capacities for Th through Am) of the actinide metals are compiled in Table 17.1. Sublimation enthalpies have been correlated with metal structures and electronic energy levels [27,28]. 

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