Cation ionic potential

Cation Ionic potential ) Species Acidity-basicity... 

Exchangeable cation Ionic potential, nm Misono softness, nm Water activity nh , mol kg mol ... 

Fig. 2.65 Influence of some minor eomponents on viscosity of clinker melt (after [39]) cation ionic potential (z/r) (i), bond energy (2)...

The data given should serve only as reference values following the rule, the higher the ionic potential, the thicker the hydration layer of the water molecules around the ion, and the slower the ionic diffusion. Cations generally diffuse more rapidly than anions. 

Standard ionic potentials Ajy can be calculated from the ionic distribution coefficients or transfer energies see Eq. (30). In order to perform such calculations, an appropriate nonthermodynamic assumption that allows division of the E> mx) or electrolyte function into ionic constituents has to be made. At the present time, the assumption about the equality of the transfer energies of tetraphenylarsonium cations (TPhAs ) and tetra-phenylborate anions (TPhB ) is considered as most appropriate [2,36]. It can be presented in the following form ... 

Table 2.3 gives the self-diffusion coefficients of some important ions in submerged soils and Figure 2.2 shows the values for the elemental ions plotted against ionic potential ( z /r where z is the absolute ionic charge and r the crystal ionic radius). As the ionic potential increases the hydration layer of water molecules around the ion increases, and therefore the mobility tends to decrease. Also, at the same ionic potential, cations diffuse faster than anions. The mobilities... 

Beryllium is normally divalent in its compounds and, because of its high ionic potential, has a tendency to form covalent bonds. In free BeX2 molecules, the Be atom is promoted to a state in which the valence electrons occupy two equivalent sp hybrid orbitals and so a linear X—Be—X system is found. However, such a system is coordinatively unsaturated and there is a strong tendency for the Be to attain its maximum coordination of four. This may be done through polymerization, as in solid BeCk, via bridging chloride ligands, or by the Be acting as an acceptor for suitable donor molecules. The concept of coordinative saturation can be applied to the other M"+ cations, and attempts to achieve it have led to attempts to deliberately synthesize new compounds. 

Various parameters such as the heat of oxide formation, ionic potential, electronegativity, and the extent of cation exchange have been proposed to control the redox properties. However, a full understanding is lacking. Nonetheless, the following trends are evident ... 

Figure 15.10 Enthalpies of formation of orthosilicates versus the ionic potential (z/r) of , alkaline earth, and O, transition metal cations.

The actinide ions in 5+ and 6+ oxidation states are prone to severe hydrolysis as compared to lower oxidation states in view of their high ionic potentials. Consequently, these oxidation states exist as the actinyl ions MOt and MO + even under acidic conditions, which can further hydrolyze under high pH conditions. The oxygen atoms of these ions do not possess any basic property and thus do not interact with protons. The tetravalent ions do not exist as the oxy-cations and can be readily hydrolyzed at low to moderate pH solutions. The degree of hydrolysis for actinide ions decreases in the order M4 > MOT > M3 > MOt, which is similar to their complex formation properties (4). In general, the hydrolysis of the actinides ions can be represented as follows ... 

As silicate minerals decompose, trace elements are released and enter the soil solution. Thereafter their fate depends on a number of factors. Immediately, they may precipitate or remain in solution and the likelihood of this happening can be predicted by considering the ion s charge/radius (in nm) ratio, which is often called the ionic potential (IP). Values of IP > 95 refer to soluble anions of the elements B, Cr(VI), Mo(VI), Si and W. Soluble cations are found in a group where IP < 30, namely Cd, Co, Cu, Fe(II), Pb, Mn(II), Hg, Ni, Ag, Sr, Sn and Zn. 

Thus the partial ionic model of Pearson and Gray (13), and very similar models of greater sophistication (14, 15) show that a very major consideration in causing deviations from the ionic model is the size of the ionization potential of the exposed orbitals of the cations, as compared with the ionic potential of a negative charge placed distance re from the... 

Besides the functional groups, the properties of cations also affect the interactions. Similar to electrostatic interactions with the layer charge, the ionic potential (the ratio of charge to ionic radius), that is, the hard and soft character of the ions (Pearson 1963, 1968 Buffle and Stumm 1994) is important. 

The hydration of hemihydrate or anhydrite shows interesting similarities to and differences from that of C3S (G49). Many foreign ions accelerate or retard hydration, but the sequences of effectiveness differ markedly from those found for C3S. Excess SO4, but not excess of Ca, is a particularly strong accelerator. Murat el al. (MI07) found that, for anhydrite, the effectiveness of an added cation decreased with its ionic potential, z/r. and considered that the cations mainly affected the rate of nucleation. The relation to z/r is almost the reverse of what is found with C3S hydration. 

In IPC, the potential difference between the stationary phase and the bulk eluent develops because of the different adsorbophilicities of the anion and cation of the IPR. The potential determining ion is the ionic species of the IPR that experiences the strongest tendency toward adsorption onto the stationary phase it may be either the anion or the cation. The potential determining ion is the actual ionpairing reagent. 

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