Polarity | 极性

📚 Polarity | 极性

Polarity is a fundamental concept in Edexcel A-Level Chemistry that describes how electrons are distributed in bonds and molecules. It explains why some molecules have partially charged ends and how these charges influence physical properties such as boiling point and solubility. Mastering polarity requires combining electronegativity, molecular shape, and symmetry.

极性是 Edexcel A-Level 化学中的一个核心概念，描述电子在化学键和分子中的分布方式。它可以解释为什么一些分子具有部分带电的两端，以及这些电荷如何影响沸点、溶解度等物理性质。掌握极性需要结合电负性、分子形状和对称性进行判断。

1. What is Polarity? | 什么是极性？

Polarity arises when a bond or molecule has an uneven distribution of electron density. In a covalent bond, electrons are shared between two atoms, but this sharing is not always equal. If one atom attracts the bonding pair more strongly, one end becomes slightly negative (δ⁻) and the other slightly positive (δ⁺).

当化学键或分子中电子密度分布不均匀时，就会产生极性。在共价键中，两个原子共享电子，但这种共享并不总是均等。如果一个原子对成键电子对的吸引更强，一端就会带上部分负电荷（δ⁻），另一端带上部分正电荷（δ⁺）。

Polarity can occur at two levels: bond polarity and molecular polarity. A molecule may contain polar bonds but still be non-polar overall if the bond dipoles cancel by symmetry.

极性可以出现在两个层面：键的极性和分子的极性。一个分子可能含有极性键，但如果键的偶极因对称性而相互抵消，分子整体仍可能是非极性的。

2. Electronegativity and Bond Polarity | 电负性与键的极性

Electronegativity is the power of an atom to attract the bonding pair of electrons in a covalent bond. The Pauling scale gives fluorine the highest value of 4.0, while caesium has one of the lowest values. A difference in electronegativity (Δχ) between two bonded atoms creates bond polarity.

电负性是原子在共价键中吸引成键电子对的能力。鲍林标度中氟的电负性最高，为 4.0，而铯是最低值之一。两个成键原子之间的电负性差值（Δχ）会产生键的极性。

Typical Edexcel rules are: Δχ = 0 to 0.4 gives a non-polar covalent bond, Δχ = 0.4 to 1.7 gives a polar covalent bond, and Δχ

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