Ionic refraction, molar

The molar refractivity of a compound can be calculated from the contributions of each of the constituent ions. The molar refractivity for the compound A By, for example, is given by the sum of the ionic refractivities of the constituent ions, R , times their concentration in the compound, or, in this case ... 

Since a typical glass contains from 50 to 80 atomic percent of anions, the ionic refractivities of the anions are very important in controlling the molar refractivity. The polarizabilities of the common anions increase in the order F < OFl < Cl" < < S " < Se < Te. This... 

Fig. 4.1 The ionic surface tension decrement, dy/dci/mN m mol dm, plotted against the ionic excess molar refractivity, R lz —Rw in cm mol ( ) anions and (A) cations...

An alternative to improving atomic/ionic refractions was to express molecular refraction through bond increments. A system of bond refractions is definitely superior to the system of atomic refractions, as it allows to account for chemical interactions explicitly. The concept of bond refraction was introduced by Bachinskii [183] who suggested that the molar refraction (as well as volumes, heats of combustion, etc) of organic compounds can be calculated of bond increments. According to Bachinskii, Rc-c =l/4f c + l/4 c. = l/47Jc + etc. This method is not quite con-... 

The apparent molar volume of interfacial water in AOT-reversed micelles is lower and its refractive index is greater than that of pure water. These findings, together with other experimental evidence, emphasize that these water molecnles are destructured, immobilized, and polarized by the ionic head of AOT [2,84,89]. In particular, it has been reported that the... 

We are forced to reflect that the failure of so many attempts to improve on the DH theory can be attributed to a premature rejection of the DH approach, and a tendency to include extra parameters without proper theoretical foundation. It is surprising that although ionic polarization is emphasized in studies of solvation (36), molten salts (37), and chemistry in general (38), the phenomenon has received little attention in interionic theory. In particular, our attention is drawn to the early work of Fajans and co-workers (39), who first noted the effects of concentration on the ionic molar refractivities of solutions, which were interpreted in terms of a distorting effect on the ions. For various reasons the significance of this work has not been appreciated in the field of electrochemistry. 

In contrast to molar polarisation calculated from optical refractivities, that calculated from relative permittivities observed at lower frequencies is by no means always independent of temperature. Actually, materials tend to fall into one of two classes. Those in one class show a relatively constant molar polarisation in accord with the simple Clausius-Mosotti relation, whilst the members of the other class, which contains materials with high relative permittivities, show a molar polarisation that decreases with increase in temperature. Debye recognised that permanent molecular dipole moments were responsible for the anomalous behaviour. From theories of chemical bonding we know that certain molecules which combine atoms of different electronegativity are partially ionic and consequently have a permanent dipole moment. Thus chlorine is highly electronegative and the carbon-chlorine... 

The interaction between a glass and light is related to the susceptibility of displacement of electrical charge, which in turn is related to the polarizability. Ionic polarizability increases with the size of ions involved however, structural considerations are also important. Refractive index (see Table 1), dielectric constant, polarizability, and molar volume are related in the molar refractivity, Rm. 

Wasastjerna (1923) divided the interionic distances in the alkali halides and alkaline-earth oxides in the ratios of the molar refractivities of the ions, taking the molar refractivity of an ion to be roughly proportional to its volume. Goldschmidt adopted Wasastjerna s values for F (1-33 A) and (1-32 A) and extended the list of radii by using the observed interionic distances in many other essentially ionic crystals. 

A single homogeneous phase such as an aqueous salt (say NaCl) solution has a large number of properties, such as temperature, density, NaCl molality, refractive index, heat capacity, absorption spectra, vapor pressure, conductivity, partial molar entropy of water, partial molar enthalpy of NaCl, ionization constant, osmotic coefficient, ionic strength, and so on. We know however that these properties are not all independent of one another. Most chemists know instinctively that a solution of NaCl in water will have all its properties fixed if temperature, pressure, and salt concentration are fixed. In other words, there are apparently three independent variables for this two-component system, or three variables which must be fixed before all variables are fixed. Furthermore, there seems to be no fundamental reason for singling out temperature, pressure, and salt concentration from the dozens of properties available, it s just more convenient any three would do. In saying this we have made the usual assumption that properties means intensive variables, or that the size of the system is irrelevant. If extensive variables are included, one extra variable is needed to fix all variables. This could be the system volume, or any other extensive parameter. 

Effective ionic radius from crystallographic data (nm) Solvent radius in nm defined as rs = [(Vs x 10 )/(8Nav)] Molar refractivity of an ion... 

Vieillard P (1987) A new set of values for Pauling s ionic radii. Acta Cryst B43 513-517 Iwadate Y, Fukushima K (1995) Electronic polarizability of a fluoride ion estimated by refractive indexes and molar volumes of molten eutectic LiF-NaF-KF. 1 Chem Phys 103 6300-6302... 

Reddy RR, Goptil KR, Ahtunmed YN et ai (2(X)5) Correlation between optical electronegativity, molar refraction, ionicity and density of binary oxides, silicates and minerals. Solid Sate Ionics 176 401-407... 

Mobile-phase velocity, 772, 773, 775 Mobilities, ionic, 635 Modem, 9, 106 Modes, normal, 437-438 Modulation, 115-116 refractive-index, 179, 214 Molar absorptivity, 1.58,367,375 Molecular... 

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