Ionic Radii

ionic radii

[ī′än·ik ′rād·ē‚ī]
(physical chemistry)
Radii which can be assigned to ions because the rapid variation of their repulsive interaction with distance makes them repel like hard spheres; these radii determine the dimensions of ionic crystals.

Ionic Radii


arbitrary characteristics of ions used for an approximate estimation of the internuclear distances in ionic crystals. The values of ionic radii are related in a regular fashion to the positions of the elements in Mendeleev’s periodic system. Ionic radii are widely used in crystal chemistry, making it possible to reveal the structural relationships in crystals of various compounds, and in geochemistry, for studies of ion substitution phenomena in geochemical processes.

Several systems of values of ionic radii have been proposed. As a rule, they are based on the following observation: the difference in the internuclear distances A-X and B-X in ionic crystals of composition AX and BX, where A and B are metals and X is a nonmetal, is virtually constant when an analogous nonmetal is substituted for X (for example, substituting bromine for chlorine), provided that the coordination numbers of the analogous ions are identical in the salts being compared. From this it follows that ionic radii have the property of additivity—that is, the experimentally determined internuclear distances may be regarded as the sum of the corresponding ionic “radii.” The breakdown of the sum into components is always based on more or less arbitrary assumptions. The systems of ionic radii proposed by various authors differ mainly in the use of various initial assumptions.

Ionic radii are tabulated for various values of the oxidation number. When its value is different from +1, the oxidation number does not correspond to a real degree of ionization of atoms, and the corresponding ionic radii acquire an even more arbitrary meaning, since the bond may be covalent to a considerable degree. The values of some ionic radii (in angstroms) for some elements (according to N. V. Belov and G. B. Bokii) are as follows: F-, 1.33; Cl-, 1.81; Br,- 1.96; I-, 2.20; O21.36; Li+, 0.68; Na+, 0.98; K+, 1.33; Rb+, 1.49; Cs+, 1.65; Be2+, 0.34; Mg2+, 0.74;Ca2+, 1.04; Sr2+, 1.20; Ba2+, 1.38; Sc3+, 0.83; Y3+, 0.97; La3+, 1.04.


References in periodicals archive ?
There was an increment of the cell parameters with ionic radii of alkaline earth element as expected whereas the change of the a/c ratio can show that there was also redistribution of ions on the sites A1 and A2 depending on the kind of the alkaline earth element.
Because the ionic radii of Sr2+, Yb3+ and In3+ are larger than those of Ca2+ and Fe3+, there is lower activation energy required for oxygen ion conductivity than CaFe2O4 type materials.
This infers the crystalinity of ZnO particles might be distorted by the introduction of dopant and whose ionic radii are lesser than that of Zn.
The variation can be explained on the basis of ionic radii of the substituted ions.
Dopant owns physical properties like higher ionic radii mobility and preference occupancy were the reasons for generation impurity phases.
Adoption of this thesis and establishment of such an effect would not be possible without the new data on the Earth composition [4], the ionic radii in eightfold coordination [5] and, of course, determination of REE concentrations in rock fractions through the methods of mass spectrometry with an inductively coupled plasma (ICP MS) and their capabilities in geochemical studies [6].
2+] is established, which depends on the hydrated ionic radii as well as on the CEC values and the observed cation mobility.
10-50 [micro]mol/L) in the circulation are drastically different, but their respective ionic radii are very similar (0.
Using ionic radii and one of the two coordination types (for glassformer cations and for modifier cations), they found that the additive density method gives agreement with experimental results in both the borate and silicate systems to within a mole fraction of 5%.
Reverse osmosis affects separation of even smaller solutes, including salts with ionic radii in the angstrom range.
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15] which attributes to the increase of Si-O distance caused by substitution of the small ionic radii of silicon by the larger ionic radii of vanadium.