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Ion polarization is the phenomenon in which ions deform under the influence of external factors (electric fields or temperature), resulting in the formation of (induced) dipole moments. In ionic compounds, ion polarization includes both the attraction of one ion to another ion, causing it to become polarized, and the deformation of an ion itself due to the attraction by another ion. It is commonly expressed in terms of the polarizing power and deformability of the ions. The polarizing power of an ion is its ability to deform other ions, that is, the electric field force exerted by an ion on other ions, and it is proportional to its ionic potential φ (n/ρn, where n is the charge number of the ion and ρn is its radius). Deformability is commonly measured by polarizability. Polarizability (α) is the induced dipole moment that arises when an ion deforms under the action of a unit effective electric field strength generated by other ions; that is, α = μ/F, where μ is the induced dipole moment and F is the effective electric field strength produced by the other ions. Generally speaking, the greater the charge of a cation, the smaller its radius; that is, the larger φ is, the greater its polarizing power will be, while its deformability or polarizability will be smaller. Conversely, the greater the charge of an anion, the larger its radius; that is, the smaller φ is, the lesser its polarizing power will be, and its deformability or polarizability will be greater. The electron shell configuration of an ion also has a significant impact on its polarizing ability. When ions have the same charge and similar radii, their deformability or polarizability increases as the number of d electrons in their outer shell increases. Therefore, the order of polarization strength is: (18+2)e-type ions > 18e-type ions > (9–17)e-type ions > 8e or 2e-type ions. As can be seen from the above, although both cations and anions possess properties related to polarizing power and deformability, when discussing polarization between cations and anions, emphasis is often placed on the polarizing power of cations and the deformability (polarizability) of anions. Only when the electron configuration of the ion is that of a non-noble gas atom does it become necessary to take both into account, that is, to consider the mutual polarization effect between the cation and the anion (also known as additional polarization). Furthermore, as the temperature increases, ionic polarization strengthens. The result of ionic polarization is the deformation of cations and anions, the overlap of their electron clouds, a decrease in bond length, and an increase in the binding energy of the crystal. The polarity of the bond is reduced due to the generation of an induced dipole moment in the opposite direction, and the coordination number of the ion is also decreased as a result of the deviation from a spherical shape. This is reflected in the properties of the crystal; for example, as polarization increases, solubility decreases and the melting point drops, among other things. In extreme cases with a very high degree of polarization. If a change in the type of bond occurs, then what is being discussed is no longer a crystal bonded by ionic bonds, but one bonded by covalent bonds. In AB-type compounds, as the valences of A and B increase, the degree of polarization becomes more pronounced; therefore, high-valence AB-type compounds are mostly covalent crystal structures. The ionic polarization theory modifies the \"rigid sphere ionic bond theory.\" As an important supplement to the ionic bond theory, it has various applications in inorganic chemistry. However, ionic compounds are only a part of inorganic compounds; therefore, it is important to be aware of the limitations of this perspective when applying it.