Ionic-dissociation theory

Nernst s point of entry into ionic and electronic theories in chemistry, then, was electrolysis and solution theory, in the mainstream of the "Ionist" dissociation theory. Indeed, van t Hoff similarly proposed an ionic theory of the polar molecule in 1895, speculating on the binding forces between 0+ and O- ions in the 02 molecule. 114... 

The energy dissipation of a system containing free charges subjected to electric fields Is well known but this Indicates a non-equilibrium situation and as a result a thermodyanmlc description of the FDE Is Impossible. Within the framework of interionic attraction theory Onsager was able to derive the effect of an electric field on the Ionic dissociation from the transport properties of the Ions In the combined coulomb and external fields (2). It is not improper to mention here the notorious mathematical difficulty of Onsager s paper on the second Wien effect. 

The first clear definition of acidity can be attributed to Arrhenius, who between 1880 and 1890 elaborated the theory of ionic dissociation in water to explain the variation in strength of different acids.3 Based on electrolytic experiments such as conductance measurements, he defined acids as substances that dissociate in water and yield the hydrogen ion whereas bases dissociate to yield hydroxide ions. In 1923, J. N. Brpnsted generalized this concept to other solvents.4 He defined an acid as a species that can donate a proton and defined a base as a species that can accept it. This... 

Valence bond (VB) theories or empirical valence bond (EVB) methods have been developed in order to solve this problem with bond potential functions that (i) allow the change of the valence bond network over time and (ii) are simple enough to be used efficiently in an otherwise classical MD simulation code. In an EVB scheme, the chemical bond in a dissociating molecule is described as the superposition of two states a less-polar bonded state and an ionic dissociated state. One of the descriptions is given by Walbran and Kornyshev in modeling of the water dissociation process.4,5 As... 

Solvent effects in electrochemistry are relevant to those solvents that permit at least some ionic dissociation of electrolytes, hence conductivities and electrode reactions. Certain electrolytes, such as tetraalkylammonium salts with large hydrophobic anions, can be dissolved in non-polar solvents, but they are hardly dissociated to ions in the solution. In solvents with relative permittivities (see Table 3.5) s < 10 little ionic dissociation takes place and ions tend to pair to neutral species, whereas in solvents with 8 > 30 little ion pairing occurs, and electrolytes, at least those with univalent cations and anions, are dissociated to a large or full extent. The Bjerrum theory of ion association, that considers the solvent surrounding an ion as a continuum characterized by its relative permittivity, can be invoked for this purpose. It considers ions to be paired and not contributing to conductivity and to effects of charges on thermodynamic properties even when separated by one or several solvent molecules, provided that the mutual electrostatic interaction energy is < 2 kBT. For ions with a diameter of a nm, the parameter b is of prime importance ... 

The identicalness of the ionization sites in a linear polyelectrolyte (Tanford, 1961) stimulated the interest of Walter and Jacon (1994) in a possible relationship between Kz and M of ionic polysaccharides displaying the characteristic titration curve of a weak, monobasic acid. Without any theoretical assumption, Eq. (S.4) was derived from simple algebra by combining elementary principles of the dissociation theory of weak acids with polymer segment theory ... 

For higher ionic strength, e g. highly saline waters the PITZER equation can be used (Pitzer 1973). This semi-empirical model is based also on the DEBYE-HUCKEL equation, but additionally integrates virial equations (vires = Latin for forces), that describe ion interactions (intermolecular forces). Compared with the ion dissociation theory the calculation is much more complicated and requires a... 

The most common approach used by geochemical modeling codes to describe the water-gas-rock-interaction in aquatic systems is the ion dissociation theory outlined briefly in chapter 1.1.2.6.1. However, reliable results can only be expected up to ionic strengths between 0.5 and 1 mol/L. If the ionic strength is exceeding this level, the ion interaction theory (e.g. PITZER equations, chapter 1.1.2.6.2) may solve the problem and computer codes have to be based on this theory. The species distribution can be calculated from thermodynamic data sets using two different approaches (chapter 2.1.4) ... 

Furthermore, compared to the PHREEQC version from 1995, it was already possible to model kinetically controlled reactions with EQ 3/6. An advantage of EQ 3/6 over the recent PHREEQC version is that it can use both the ion dissociation theory and the PITZER equations for solutions with higher ionic strengths. 

The difficulty in explaining the effects of inorganic solutes on the physical properties of solutions led in 1884 to Arrhenius theory of incomplete and complete dissociation of ionic solutes (electrolytes, ionophores) into cations and anions in solution, which was only very reluctantly accepted by his contemporaries. Arrhenius derived his dissociation theory from comparison of the results obtained by measurements of electroconductivity and osmotic pressure of dilute electrolyte solutions [6]. 

What is the significance of these results on dimer and trimer formation for ionic solution theory In the post-Debye and HUckel world, particularly between about 1950 and 1980 (applications of the Mayer theory), some theorists made calculations in which it was assumed that aU electrolytes were completely dissociated at least up to 3 mol dm. The present work shows that the degree of association, even for 1 1 salts, is -10% at only 0.1 mol dm . One sees that these results are higher than those of the primitive Bjerrum theory. 

Certain thermal properties of electrolytes are in harmony with the theory of ionic dissociation for example, the heat of neutralization of a strong acid by an equivalent amount of a strong base in dilute solution is about 13.7 kcal. at 20 irrespective of the exact nature of the acid or base. If the acid is hydrochloric acid and the base is sodium hydroxide, then according to the ionic theory the neutralization reaction should be written... 

The nature of esters or ethereal salts has been fully discussed already in connection with the esters of inorganic acids and alcohols (p. 102). The name salts applies because they are formed by neutralizing an alcohol, acting as a base, with an acid. It must be emphasized, however, that in so terming these compounds salts we do not mean this to apply in a physical chemical sense as describing their properties in solution in accordance with the electrolytic theory of ionic dissociation. We are dealing here with questions of composition and constitution. Ethereal salts differ from metal salts, at least as to the degree of their dissociation into ions when in solution. 

Subsequent research has entirely confirmed the theory of Arrhenius. The chemical and electrochemical behaviour of solutions is closely connected with their ionic dissociation, and would be quite inexplicable without this theory. Rarely in the history of science has an idea proved so fruitful and suggestive, and led to the discovery of so many hitherto unsuspected relationships as this hypothesis of Arrhenius. 

Faraday s ions, Arrhenius proposed, were simply atoms (or groups of atoms) carrying either a positive or a negative electric charge. The ions were either the atoms of electricity or they carried those atoms of electricity. (ITie latter alternative eventually proved correct.) Arrheniuis used his theory of ionic dissociation to account for many facts of electrochemistry. 

It seemed quite clear, however, that the independence could not be complete. Arrhenius, in the 1880s, had advanced his theory of ionic dissociation (see page 161). He had explained the behavior of ions by assuming them to be electrically charged atoms or groups of atoms. At the time this had seemed nonsense to most chemists, but it seemed nonsense no longer. 

Svante August Arrhenius (1859-1927), Swedish physical chemist, astrophysicist, professor at the Stockholm University, and originator of the electrolytic theory of ionic dissociation, measurements of the temperature of planets and of the solar corona, and also of the theory deriving life on Earth from outer space. In 1903, he received the Nobel Prize in chemistry for the services he has rendered to the advancement of chemistry by tis e/ec-trolytic theory of dissociation ... 

The dissociation of an electrolyte molecule in solution into oppositely charged ions, however, is by no means a simple matter. The ionic association theory, first developed by Bjerrum in 1926, indicates that some kind of association will still exist between oppositely charged ions even when they are several molecular diameters apart. The rates of dissociation and reformation, of molecules or other complexes, are extremely fast and it is doubtful if the ions can... 

Arrhenius developed his theory on acido-basic reactions and on ionic dissociation. 

Over 100 years have passed since Arrhenius published his Dissociation Theory of Electrolytes in 1887. Prior to this it was believed that electrolytes did not dissociate into ions in water until current was passed, and Arrhenius work was not well received. It was some decades after this that Born s theory of ionic solvation, and then, Debye and Huckel s theory of ionic activities in... 

The above description of acids and bases, in which H (aq) and OH (aq) ions are viewed as responsible for acidic and basic properties, respectively, and different acidic (or electrolytic) strengths are attributed to varying degrees of ionic dissociation, was developed by the Swedish chemist S. Arrhenius between 1880 and 1890. While very useful, this theory has some problems. The first problem has to do with the nature of the positive-charge carrier in aqueous solutions the second problem is that some substances can act as bases, even though they do not release OH (aq) ions. We will now consider both of these problems. 

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