Explanation

The average distance from an atomic nucleus to its outermost electron reflects the average result of the attraction of electrons outside the nucleus and the repulsion between electrons outside the nucleus. According to quantum mechanics, the probability of the electron appearing at a certain point in space is proportional to the mode square of the wave function at that point, that is, the ion has no definite radius, so the ionic radius is a simplified concept. The distance between two adjacent ions can be calculated by measuring the lattice constant (X-ray or electron diffraction) of a known crystal; Assuming that the same ion has the same ionic radius in different crystal, the positive and negative ionic radius can be obtained. After measuring the lattice constant of ionic crystal, there are three methods to calculate the radius of positive and negative ions. ① Goldschmidt radius: compare the spacing between the same positive ion (usually metal ion) and anion (generally oxygen ion or halogen ion) in different crystal, and calculate the radius of positive and negative ions. More than 80 ion radius values have been calculated using this method; ② Pauling method: the ionic radius is not only related to the distribution of the outermost electrons, but also inversely proportional to the effective charge Z-S acting on the isoelectronic ions. ③ Zachariasen method: By compiling radius data of closed shell configuration ions.

Classification