Polarization

The role of the proton in polarizing and deforming different ions

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This entry is made by Compilation and application of scientific encyclopedia entries of "Science Popularization China" to examine.

The action of an ion to polarize and deform a different ion is called the "polarization" of the ion; The ability of the ion electron cloud to deform due to the polarization of a different ion is called the "deformability" of the ion.

Chinese name: Polarization
Foreign name: Polarisation (UK)/polarisation (US)

Charge: The higher the cation charge, the stronger the polarization
Radius: Similar charge of cation shell is equal, and the radius is small
Cause: Mutual polarization and additional polarization

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seven Interpreting phenomena

definition

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Polarization refers to radiation in the direction of maximum radiation air waves Polarization, which is defined as the trajectory of the end point of the electric field vector in the maximum radiation direction. Due to the physical structure of the antenna itself far field In addition to the movement in the required direction, there are components in the orthogonal direction of the electric field vector of, which refers to the cross polarization of the antenna. Generally, cross polarization requires that the cross polarization gain radiated in the main direction should be more than 30dB less than the main polarization gain. Of course, the requirements will change in different situations. as for microstrip antenna I haven't noticed how to reduce cross polarization, but it seems that it is better to choose a substrate with lower h (reducing the excitation of surface waves), or use the slot coupling underfeed method.

classification

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Electronic polarization: under the action of external electric field, the electronic cloud will have a small displacement relative to the atomic nucleus, making the electrically neutral atoms form a small Electric dipole 。

Ionic polarization : Under the action of the external electric field, the positive and negative ions that make up the molecule move slightly, making the molecule form a very small electric dipole.

Orientational polarization : Under the action of external electric field, the originally disorderly arranged polar molecules are converted into orderly arrangement, forming synthesis Electric moment 。

Generally, there is only electronic polarization in monatomic media. All compounds have electronic polarization and ionic polarization. Some compounds have intrinsic electric moments and other three polarizations at the same time.

stay electric field Ionic Electronic cloud When the change occurs, the dipole will be generated or the original dipole will be increased. This phenomenon is called ion polarization. Inter ion removal Electrostatic attraction Besides, there are other forces. Cations generally have small radius and positive charge, which will affect adjacent anions Induction And deform it (polarization). Anions generally have a large radius and many negative charges on the periphery, so they are prone to electron cloud deformation (ion deformability) under the action of an electric field. In fact, each ion has the dual nature of polarization that deforms the opposite ion and deformation that is caused by other ions. Cations with large charge number and small radius have strong polarization effect. With 18 Electronic layer And the ions with irregular electron layers, their deformability is greater than that of the ions with similar radius Inert gas Type I ions are much larger. For example, Ag+>K+; Hg2+>Ca2+. 4. Ions with the same structure, positive charge The more cation Deformability The smaller the number of electron layers, the greater the deformability. Large anions and small charge cations (such as Ag+, pb2+, Hg2+) with 18 electron layers or irregular electron layers are most likely to deform. The inert gas cation with small radius and high charge (such as Be2+, Al3+, Si4+, etc.) is the most difficult to deform. Ionic polarization pair Chemical bond influential. Cations and anions polarize each other, causing extra attraction between them. Therefore, when two ions are closer together, it is possible to overlap the electron clouds of the two ions and tend to generate covalent bonds with less polarity. The change of bond type will certainly affect the properties of compounds. Generally, with the increase of polarization, the melting point and boiling point of the material decrease, the color gradually deepens, and the solubility in water decreases.^[1]

Ionic polarization theory

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Ionic polarization theory yes Ionic bond theory An important supplement to. The theory of ionic polarization holds that: Ionic compound In addition to the electrostatic attraction which plays a major role in the, the inductive force plays a very important role. The ions themselves are charged. When the anions and cations are close to each other, under the influence of the opposite electric field, the electron cloud will deform, and the gravity centers of the positive and negative charges will no longer coincide, resulting in an induced dipole, which will lead to ion polarization, resulting in corresponding changes in the structure and properties of the material.

Ionic deformation

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(1) Cations with the same structure, the higher the positive charge, the smaller the deformation, (Na+)>(Mg2+)>(Al3+)>(Si4+)

(2) For ions with the same shell structure, the more electronic layers, Deformability The bigger Li+<Na+<K+<Rb+<Cs+; F-<Cl-<Br-<I-

(3) When the charge and radius are similar; 18e-,18+2e-； 9~17e ->>8e - deformability: Ag+>K+; Hg2+>Ca2+, etc

(4) For ions with the same or similar structure, the larger the radius, the greater the deformability

(5) Complex anion Deformability Usually small, central ion Oxidation number The higher the deformation is, the smaller the deformability is. ClO4 -<F -<NO3 -<CN -<Cl -<Br -<I - Summary: The most easily deformed are large anions and small charges of 18e -, 18+2e -, 9~17e - cation , such as Ag+, Pb2+, Hg2+, etc; The most difficult deformation is small radius and high charge Noble gas Shell cation, such as Be2+ Al3+, Si4+, etc. 4. Mutual polarization (additional polarization). In fact, each ion, on the one hand, as a charged body, will deform other hetero ions; on the other hand, under the action of surrounding ions, it will also deform itself. This anion cation mutual polarization results in an increase in the induced dipole moment, which further strengthens their interaction, This is the additional polarization. Obviously, the total polarization of each ion should be the sum of its original polarization and additional polarization.^[1]

Polarization law

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(1) Charge: The higher the cation charge, the stronger the polarization.

(2) Radius: when the similar charges of the cationic shell are equal, the radius is small and the polarization force is strong. For example, Li+>Na+.

(3) Ion configuration (cation): 18e -, 2e -, 18+2e -, (Ag+, Li+, Pb2+, etc.)>9~17e - (Fe2+, Ni2+, Cr3+)>8e - (Na+, Mg2+, etc.).

(4) Complex anions with high charges also have certain polarization effects, such as SO42 -, PO43 -, etc.

Some laws of mutual polarization:

(1) The positive ions of 18 and (18+2) electronic configuration are easy to deform, which is easy to cause mutual polarization and additional polarization;

(2) In the same family of the periodic system, from top to bottom, the additional polarization of 18 electron ions increases, strengthening the total polarization of this ion with negative ions;

(3) In the positive case with 18 or (18+2) electronic configuration Ionic compound The greater the deformation of negative ions, the stronger the additional polarization effect.

In a word, the more d electrons and electron layers the positive ion contains, the greater this additional polarization effect is generally.^[1]