Living reference work entry
Definition and Assumptions
An ion is an atom with an electrical charge, achieved either by gaining or losing one or more electrons. The ionic radius of the ion (r ion ) of an atom (either a cation or anion) is a measure of the size of a spherical ion. The ionic radius is similar to but different from the atomic radius for the ionic size is dependent on the distribution of its outermost electrons and is inversely proportional to the effective nuclear charge experienced by ions. It is calculated from the internuclear distance between a cation and a neighboring anion in a lattice. Ionic radii are typically reported in picometers (pm, 1 × 10 −12 m) or in the older literature as Angstroms (Å), where 1 Å = 100 pm. A typical range of ionic radii is 25–170 pm for four to eightfold coordination (see Table 1).
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