Polar bond

Covalent bond formed by different atoms

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In a compound molecule, different atoms form covalent bond , due to two atom The ability to attract electrons is different. The shared electrons must be biased towards the atom with stronger electron attraction ability, so the atom with weaker electron attraction ability is relatively obviously positive. Such covalent bonds are called Polar covalent bond , referred to as polar bond.

Chinese name: Polar bond
Foreign name: polar bond
Alias: Polar covalent bond

Interpretation: Atomic covalent bond
Features: The shift of shared electrons towards highly oxidizing particles
Definition: Covalent bond with dipole moment μ ≠ 0^[1]

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principle

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according to Front track Theoretically, the formation of polar bonds can be explained as follows: molecular orbital By the atomic frontier orbitals linear combination And become. If the electronegativity of atom A is greater than that of atom B, its frontier orbital energy level is lower than that of atom B. In the formation of covalent bond Low energy Bonding orbital The energy level of is closer to the previous frontier orbital energy level of A atom, so the bonding orbital is mainly composed of the frontier orbital of A atom; The higher energy Antibonding orbit The energy level is closer to the original frontier orbital energy level of B atom, so it is mainly composed of the frontier orbital of B atom. Since the electrons are preferentially distributed in the bonding orbital, the A atom with greater electronegativity occupies more electrons, and the polarity of covalent bond is thus generated.

Forming conditions

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Not only Nonmetallic element It is possible to form Polar covalent bond , polar covalent bonds can also be formed between metals and nonmetals (such as AlCl three ，BeCl two In general, as long as the Electronegativity If the difference is less than 1.7, a polar bond will be formed; if the difference is greater than 1.7, a polar bond will be formed Ionic bond 。

Polar key between Ionic bond and Nonpolar bond between.

Polar molecule

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If Molecular configuration Asymmetric, the molecule is Polar molecule 。

Distinguish between polar molecules and Nonpolar molecule Method: criterion for non-polar molecules: Central atom Valence Method and force analysis method.

Molecules containing polar bonds are not necessarily Polar molecule The standard to measure polar molecules is the size of the dipole distance. Only when the dipole distance is not zero, the molecules have polarity.

In the molecule,

Central atom

Composed of AB n Type compound, if the valence of central atom A absolute value Is equal to the ordinal number of the family, then the compound is a nonpolar molecule, such as CH four ，CCl four ，SO three ，PCl five 。

The absolute value of the valence of the central atom is not equal to the atom Number of outermost electrons Is polar molecule, such as HX (X is Halogen group element ）， CO ， NO ，H two O，H two S，NO two ，SO two ，SCl two ，NH three ，H two O two ，CH three Cl，CH two Cl two ，CHCl three ，CH three CH two OH。

force analysis

If known Bond angle (or space structure ）, available force analysis , where the resultant force is 0, it is a non-polar molecule, such as CO two ，C two H four ，BF three 。

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