Free ions definition

While related to its carbon analogs, the existence of the RsSi species as a free ion in condensed phases had been doubted for a long time. However, NMR characterization using bulky aryl substituents has provided evidence for the triply coordinated silicon cation. " However, definitive evidence was recently reported by the groups of Reed and Lambert with a silyl cation species bound to three mesityl groups and a carborane [HCBnMesBrg] counterion (Eig. 7.5). It was suggested that... 

The chemical behavior of ions, ion pairs, and polarizable molecules partakes of the same indistinctness as the definitions of these species. Any attempt to make a complete catalog of the reactions of ions will almost certainly include borderline reactions whose intermediates are in fact ion-pairs or even covalent molecules. For many purposes the identification of a reaction as carbonium ion-like, or what the Germans would call Krypto-ionenreaktion, is as useful as the certain knowledge that the intermediate is actually a carbonium ion. Many of the ionic reaction mechanisms in the literature do not represent actual free ions and were not so intended by their authors. The ionic representation is often merely a convenient simplification if it is an oversimplification it is one that is easily rectified when the pertinent data become available. The value of such approximate mechanisms is that... 

The first satisfactory definition of crystal radius was given by Tosi (1964) In an ideal ionic crystal where every valence electron is supposed to remain localised on its parent ion, to each ion it can be associated a limit at which the wave function vanishes. The radial extension of the ion along the connection with its first neighbour can be considered as a measure of its dimension in the crystal (crystal radius). This concept is clearly displayed in figure 1.7A, in which the radial electron density distribution curves are shown for Na and Cl ions in NaCl. The nucleus of Cl is located at the origin on the abscissa axis and the nucleus of Na is positioned at the interionic distance experimentally observed for neighboring ions in NaCl. The superimposed radial density functions define an electron density minimum that limits the dimensions or crystal radii of the two ions. We also note that the radial distribution functions for the two ions in the crystal (continuous lines) are not identical to the radial distribution functions for the free ions (dashed lines). 

The combining of two or more substances or molecular entities to yield a single substance or molecular entity, a process that involves either covalent or noncovalent bonding. Included in this definition is the formation of ion pairs from free ions, the noncovalent aggregation of monomers to form polymeric structures or complexes, as well as colligation. The opposite of association is dissociation. 

The probability of an ion remaining fixed is given by 1 — e where h is the Boltzmann gas constant == 1 372 x 10 erg/degree, T the absolute temperature. There will thus be at any definite temperature a number of free ions and ions bound to the double layer, the free ions will, as it were, form a second sheet in the double layer. 

If there is no pathway independent of the chloride, that is, if extrapolation to very low chloride concentration of chloride exchange reaction led to a zero intercept and no free ion pathway, then we would have a bimolecular reaction. This definition of bimolecularity only requires chloride to be a component of the second coordination sphere for chloride exchange to occur. 

With accumulation of the experimental data, the field effects on polymerization reactions have become more and more definite. As the causes of the effects, we have suggested two factors, namely the field-facilitated dissociation of the ion-pair growing chain ends and the desolvation of the free-ion growing ends. Further detailed study is certainly required to determine unequivocally which of the above-mentioned factors is more influential. If the true cause or causes are discovered, we can be hopeful of finding much larger upgrading effects on polymerization reactions, which are interesting from the academic and practical points of view. 

In principle, it would be logical to combine plots of the buffer index curves of each of the buffer components of milk and thus obtain a plot which could be compared with that actually found for milk. It is not difficult, of course, to conclude that the principal buffer components are phosphate, citrate, bicarbonate, and proteins, but quantitative assignment of the buffer capacity to these components proves to be rather difficult. This problem arises primarily from the presence of calcium and magnesium in the system. These alkaline earths are present as free ions as soluble, undissociated complexes with phosphates, citrate, and casein and as colloidal phosphates associated with casein. Thus precise definition of the ionic equilibria in milk becomes rather complicated. It is difficult to obtain ratios for the various physical states of some of the components, even in simple systems. Some concentrations must be calculated from the dissociation constants, whose... 

Fig. 47. Normal vibrational modes Qi and Qi compatible with Jahn-Teller splitting of the degenerate ground state of an octahedral-site 3d4 and 3d cation, (a) Definition of modes for a free ion complex. (See following pages for Figs. 47(b) and 47(c).)...

Association — The assembling of separate -> molecular entities into any aggregate, especially of oppositely charged free ions into - ion pairs or larger and not necessarily well-defined clusters of ions held together by electrostatic attraction. The term signifies the reverse of -> dissociation but is not commonly used for the formation of definite adducts by colligation or -> coordination. 

The ion pair concept, introduced by Bjerrum [14], was critically reviewed by Szwarc [15] and definitions were given based on the mutual geometry of ions and solvent. The existence of loose and tight ion pairs was suggested by Winstein [16] and Sadek [17] and it is now common to speak about free ions (FI) as well as of solvent-separated ion pairs (SSIP) or contact ion pairs (CIP), having in mind the oversimplified picture ... 

The new optical and spectroscopic methods are more discerning, more definite in what they reveal. For example, in solutions of AgNOjin water and in dimethylfor-mamide, one used to speak of ion-pair formation, Ag Oj. By now it is known that there are several kinds of ion pairs. For example, the ions may be in direct contact or they may be separated by a solvent molecule. The concentration of the free ions (if they give vibration spectra) can be followed. In general, an enormous increase in detail (corresponding to an increase in knowledge of the variety of particles present in the nonaqueous systems) has become available. 

Aqueous speciation. The distribution of dissolved components among free ions, ion pairs, and complexes. For example, dissolved iron in acid mine drainage (AMD) can be present as Fe( q) (free ferrous iron), FeS04(aq> (ion pair), Fef q) (free ferric iron), Fe(OH)(j q), and FeS04(aq) species. These species are present in a single phase, aqueous solution. Aqueous speciation is not uniquely defined but depends on the theoretical formulation of mass action equilibria and activity coefficients, i.e. it is model dependent. Some aqueous speciation can be determined analytically but operational definitions and assumptions are still unavoidable. 

For various purposes, the dissolved concentration (or even the free ion activity) in the pore water can be used to explain effects. In those cases available fraction and pore water concentration are equivalent. This is, however, only one of the definitions of bioavailability. Based on the pore water concentration (actual availability) it is possible to explain targets such as the... 

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