Chemical Bonding Explained | 化学键详解

📚 Chemical Bonding Explained | 化学键详解

In Edexcel IGCSE Science, chemical bonding is a core topic that appears in multiple choice, short answer and extended response questions. This revision guide explains the three main types of bonding, how to draw electron diagrams, and how bonding affects the properties of substances. By the end, you will be able to compare different structures and avoid common mistakes in the exam.

在 Edexcel IGCSE 科学中，化学键是核心考点，常见于选择题、简答题和扩展作答。本复习指南讲解三类主要化学键、如何画电子示意图，以及化学键如何影响物质性质。学完后，你将能比较不同结构并避开考试中的常见错误。

---

1. Why Atoms Bond | 原子为什么成键

Atoms bond to become more stable by achieving a full outer shell of electrons. For most atoms, this means having eight electrons in the outermost shell, known as the octet rule.

原子通过获得满外层电子来变得更稳定。对大多数原子而言，这意味着最外层拥有八个电子，即八隅体规则。

Atoms are made of protons, neutrons and electrons, but only the electrons in the outer shell take part in bonding. These are called valence electrons.

原子由质子、中子和电子构成，但只有最外层电子参与成键，这些电子称为价电子。

Chemical bonding is a natural process because the combined substance has lower energy and is more stable than the separate atoms.

化学键的形成是自然过程，因为结合后的物质能量更低，比孤立的原子更稳定。

Noble gases such as neon and argon already have a full outer shell, so they rarely react or form bonds.

稀有气体如氖、氩已经具有满电子外壳，因此很少发生反应或形成化学键。

---

2. The Octet Rule | 八隅体规则

The octet rule states that atoms tend to gain, lose or share electrons in order to achieve eight electrons in their outermost shell, which is a stable electronic arrangement.

八隅体规则指出，原子倾向于获得、失去或共享电子，以使最外层达到八个电子，这是一种稳定的电子排布。

For example, sodium has the electronic configuration 2.8.1. It is easier for sodium to lose one electron than to gain seven, so it forms a sodium ion with charge +1.

例如，钠的电子排布为 2.8.1。对钠来说，失去一个电子比获得七个更容易，因此它形成带 +1 电荷的钠离子。

Chlorine has the configuration 2.8.7. It gains one electron to fill its outer shell, forming a chloride ion with charge -1.

氯的排布为 2.8.7。它获得一个电子来填满外壳，形成带 -1 电荷的氯离子。

Hydrogen is an exception: it only needs two electrons to be stable because its first shell can hold a maximum of two electrons.

氢是例外：它只需要两个电子即可稳定，因为其第一层最多只能容纳两个电子。

---

3. Ionic Bonding | 离子键

Ionic bonding occurs between a metal and a non-metal. The metal atom transfers one or more electrons to the non-metal atom, creating positive and negative ions.

离子键发生在金属和非金属之间。金属原子将一个或多个电子转移给非金属原子，产生正离子和负离子。

The ionic bond is the strong electrostatic force of attraction between these oppositely charged ions.

离子键就是这些带相反电荷离子之间的强静电吸引力。

Example: sodium loses one electron to form Na⁺; chlorine gains one electron to form Cl⁻. The electron transfer can be shown as:

例子：钠失去一个电子形成 Na⁺；氯获得一个电子形成 Cl⁻。电子转移可表示为：

Na → Na⁺ + e⁻

Cl + e⁻ → Cl⁻

Overall, the formula of sodium chloride is NaCl, not Na₂Cl, because the charges balance: one Na⁺ pairs with one Cl⁻.

因此，氯化钠的化学式是 NaCl，而不是 Na₂Cl，因为正负电荷平衡：一个 Na⁺ 与一个 Cl⁻ 配对。

In the solid state, the ions are arranged in a giant ionic lattice structure, where each positive ion is surrounded by negative ions and vice versa.

在固态下，离子排列成巨型离子晶格结构，每个正离子周围被负离子包围，反之亦然。

---

4. Properties of Ionic Compounds | 离子化合物的性质

Ionic compounds have high melting and boiling points because the strong electrostatic forces between ions require a large amount of energy to overcome.

离子化合物具有较高的熔沸点，因为克服离子间强烈的静电作用力需要大量能量。

They do not conduct electricity when solid because the ions are fixed in the lattice and cannot move.

固态时不导电，因为离子固定在晶格中无法移动。

When molten or dissolved in water, the ions are free to move, so the substance conducts electricity.

当熔融或溶于水时，离子可以自由移动，因此能够导电。

Ionic solids are hard but brittle: a sudden impact can shift layers of ions, causing repulsion between like charges and making the crystal shatter.

离子固体质地坚硬但性脆：突然的撞击会使离子层错位，导致同种电荷相互排斥，使晶体碎裂。

---

5. Covalent Bonding | 共价键

Covalent bonding occurs between non-metal atoms. Instead of transferring electrons, the atoms share pairs of electrons so that

Published by TutorHao | IGCSE Science Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）