Gaseous ions

Castleman A W and Mark T D 1986 Cluster ions their formation, properties, and role in eluoidating the properties of matter in the oondensed state Gaseous Ion Chemistry and Mass Spectrometry ed J FI Futrell (New York Wiley)... 

Element Ionisation energy (kj mof ) Metallic radius (nm) Ionic radius (nm) Heal oj laporibation at 298 K (kJ mol ) Hydration energy oj gaseous ion (kJ moI ) (V)... 

Thermodynamic. Thermodynamic properties of Pu metal, gaseous species, and the aqueous ions at 298 K are given in Table 8. Thermodynamic properties of elemental Pu (44), of alloys (68), and of the gaseous ions Pu", PuO", PuO" 27 PuO 2 (67) have been reviewed, as have those of aqueous ions (64), oxides (69), haUdes (70), hydrides (71), and most other compounds (65). 

The rates of these reactions bodr in the gas phase and on the condensed phase are usually increased as the temperature of die process is increased, but a substantially greater effect on the rate cati often be achieved when the reactants are adsorbed on die surface of a solid, or if intense beams of radiation of suitable wavelength and particles, such as electrons and gaseous ions with sufficient kinetic energies, can be used to bring about molecular decomposition. It follows drat the development of lasers and plasmas has considerably increased die scope and utility of drese thermochemical processes. These topics will be considered in the later chapters. 

Gaseous ion diffusion A method of charging particles in an electrostatic precipitator. 

The HC1 molecule is a stable one—it must be heated to a few thousand degrees before the atoms will separate. Even then, neutral atoms are obtained and still higher temperatures are needed before gaseous ions are obtained. 

Every mass spectrometer consists of four principal components (Fig 1) (1) the source, where a beam of gaseous ions are produced from the sample (2) the analyzer, where the ion beam is resolved into its characteristic mass species (3) the detector, where the ions are detected and their intensities measured (4) the sample introduction system to vaporize and admit the sample into the ion source. There is a wide variety in each of these components and only those types which are relevant to analytical and organic mass spectrometry will be emphasized in this survey. The instrumentation... 

The lattice enthalpy can be identified with the heat required to vaporize the solid at constant pressure. The greater the lattice enthalpy, the greater is the heat required. Heat equal to the lattice enthalpy is released when the solid forms from gaseous ions. In Section 2.4 we calculated the lattice energy and discussed how it depended on the attractions between the ions. The lattice enthalpy differs from the lattice energy by only a few kilojoules per mole and can be interpreted in a similar way. 

The lattice enthalpy of a solid cannot be measured directly. However, we can obtain it indirectly by combining other measurements in an application of Hess s law. This approach takes advantage of the first law of thermodynamics and, in particular, the fact that enthalpy is a state function. The procedure uses a Born-Haber cycle, a closed path of steps, one of which is the formation of a solid lattice from the gaseous ions. The enthalpy change for this step is the negative of the lattice enthalpy. Table 6.6 lists some lattice enthalpies found in this way. 

In a Born-Haber cycle, we imagine that we break apart the bulk elements into atoms, ionize the atoms, combine the gaseous ions to form the ionic solid, then form the elements again from the ionic solid (Fig. 6.32). Only the lattice enthalpy, the enthalpy of the step in which the ionic solid is formed from the gaseous ions, is unknown. The sum of the enthalpy changes for a complete Born-Haber cycle is zero, because the enthalpy of the system must be the same at the start and finish. 

In the second hypothetical step, we imagine the gaseous ions plunging into water and forming the final solution. The molar enthalpy of this step is called the enthalpy of hydration, AHhvd, of the compound (Table 8.7). Enthalpies of hydration are negative and comparable in value to the lattice enthalpies of the compounds. For sodium chloride, for instance, the enthalpy of hydration, the molar enthalpy change for the process... 

We are now led to introduce a second empirical correction into our calculations. The theoretical values for the rubidium, caesium, bromide, and iodide ions in Table III resulted from the assumption that SE is independent of Z, which is known not to be true for these structures, on account of the difference between SE<1 and SEw. The solution values of R, which we may assume to hold also for gaseous ions in these cases, also show that the screening constant for the negative ions should be larger and for the positive ions smaller than that used that is, as Z increases SE decreases, presumably approaching our theoretical values for Z large. We shall assume that SE is a linear function of Z in this region, and evaluate the parameters of the function with the use of the solution values for the bromide and iodide ions. If we write... 

In Table IV are given values of the mole refraction of gaseous ions calculated from equations (24) and (29) with the use of the values found above for SE and ASe. Values for hydrogen-like atoms and ions are also included these are, of course, accurate, since no screening constant is needed. Table IV is... 

The available experimental data, because of their paucity and their inaccuracy, do not permit the extensive testing of these figures. The directly determined susceptibilities for helium, neon, and argon are in gratifying agreement with the theoretical ones (Table YI). From the mole refraction results we may expect ions in solution to have values of % near those for gaseous ions. KoenigsbergerJ has made determinations of % for seven alkali halides in aqueous solution, in... 

In the lanthanide series, the equivalent values are much reduced by the retreat of the 4f electrons into the xenon core. This is so whether we consider processes that involve the condensation of gaseous ions, or conventional reactions. Table 1.3 includes data for the change... 

Na (g) + Cl (g) NaCK. ) A -calculated - - 769 kJ/mol This Is the energy released when the solid forms from separated gaseous ions. The reverse process, in which an ionic solid decomposes into gaseous ions, is termed the lattice energy (LE) and is a positive quantity ... 

The second stage is the salvation or hydration of these gaseous ions in water to provide solvated or hydrated ions in solution accompanied by the evolution of their heats of solvation or hydration as represented below ... 

AHs may be either positive or negative. That principally depends on the relative magnitudes of the terms that figure on the right-hand side of the equation. In some cases heat is evolved on the dissolution of a salt in water. It is mainly due to the fact that heat evolved when the gaseous ions are hydrated (AHX) is more than the heat absorbed in rupturing the crystal lattice. In the majority of cases, however, there is an absorption ofheat when a salt dissolves in water. 

Mass spectrometry involves the study of ions in the vapour phase. Mass spectrometers are analytical instruments that convert neutral molecules into gaseous ions and separate those ions according to the ratio of their mass-to-charge (m/z) The location of the mass lines provides a qualitative analysis, and their intensity, mostly measured relative to that of the matrix element or a suitable internal standard, gives a quantitative analysis. 

Casdeman, Jr., A. W. Mark, T. D. In Gaseous Ion Chemistry/Mass Spectrometry John Wiley and Sons, New York, 1986, Chapter 12, pp 259-303. 

Held, F. H. Franklin, J. L. Electron Impact Phenomena and the Properties of Gaseous Ions Academic Press New York, 1957. 

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