Polar covalent bond

Chemical bond

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Atomic passage Shared electron pair The interaction formed is called covalent bond It can be attractive or repulsive. In compound molecules, when different atoms form covalent bonds, because the ability of atoms to attract electrons is different, sharing electron pairs will tend to the side with strong ability to attract electrons, the side with strong ability to attract electrons will be negative, and the side with weak ability to attract electrons will be positive. such Electron pair The offset covalent bond is called polar covalent bond Polar bond 。 In the polar key, Nonmetallic Relatively strong, Metallicity The relatively weak element atoms are negatively charged at one end; The atoms of elements with relatively weak nonmetallic properties and relatively strong metallicity are positively charged at one end.

Chinese name: Polarity covalent bond
Foreign name: polar covalent bond

Applicable fields: Chemistry
Applied discipline: Chemistry（ First level discipline ）
Definition: Covalent bond with dipole moment μ ≠ 0

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brief introduction

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In polar bonds, the greater the non-metallic difference of bonding elements, covalent bond The more obvious (stronger) the polarity of; The smaller the non-metallic difference of bonding elements, the less obvious (weaker) the polarity of covalent bonds.

Polar covalent bond

according to frontier orbital To understand, Polar bond This can be explained as follows. because molecular orbital By the atomic frontier orbitals linear combination And become. If A atomic Electronegativity If it is larger than B atom, its frontier orbital energy level is lower than that of B atom. In the formation of covalent bond Low energy Bonding orbital The energy level of (Bonding Orbital) 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 (Anti Bonding Orbital) energy level is closer to the original frontier orbital energy level of B atom, so it is mainly composed of Front track Composition. Since electrons are preferentially distributed in bonding orbitals, Electronegativity The larger A atom occupies more electrons, and the polarity of the covalent bond is thus generated.

Covalent The polarity of a molecule is equal to all covalent bonds in the molecule dipole moment So the molecule composed of polar covalent bond can be Polar molecule （ Hydrogen chloride ）It can also be Nonpolar molecule （ carbon dioxide ）。 and nonpolar covalent bond It exists in simple substances and also in some compounds Nonpolar bond The molecules formed must be nonpolar molecules (but some nonpolar molecules contain polar bonds).

example

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HCl molecule, Cl has a stronger ability to attract electrons than H, and the shared electron pair is biased towards Cl, Cl is relatively negatively charged, The H side is relatively positive.

Forming conditions

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Not only Nonmetallic element It is possible to form polarity between covalent bond , polar covalent bonds can also be formed between metals and nonmetals (such as AlCl3 ）In general, as long as the electronegativity between two non-metallic atoms is different and the difference is less than 1.7, a polar bond is formed; when the difference is greater than 1.7, a polar bond is formed Ionic bond 。

Some values of electronegativity difference are attached below for your convenience:

Electronegativity of common elements（ Pauling scale ）

Hydrogen 2.2 Lithium 0.98 Beryllium 1.57 Boron 2.04 Carbon 2.55 Nitrogen 3.04 Oxygen 3.44 Fluorine 3.98

Sodium 0.93 Magnesium 1.31 Aluminum 1.61 Silicon 1.90 Phosphorus 2.19 Sulfur 2.58 Chlorine 3.16

Potassium 0.82 calcium 1.00 manganese 1.55 iron 1.83 nickel 1.91 copper 1.9 zinc 1.65 gallium 1.81 germanium 2.01 arsenic 2.18 selenium 2.48 bromine 2.96

Rubidium 0.82 Strontium 0.95 Silver 1.93 Iodine 2.66 Barium 0.89 Gold 2.54 Lead 2.33

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