📚 Ionic and Covalent Bonding | 离子键与共价键
In IGCSE Edexcel Science (Chemistry), the concepts of ionic and covalent bonding are fundamental to understanding how atoms join to form compounds with different properties. This revision guide breaks down the key ideas you need to master for your exams.
在IGCSE Edexcel科学（化学）中，离子键和共价键的概念是理解原子如何结合形成具有不同性质的化合物的基础。这份复习指南拆解了考试中必须掌握的核心要点。
1. Introduction to Bonding | 键合简介
Atoms of different elements can combine to form compounds through chemical bonding. The type of bonding depends on how the atoms achieve a more stable electronic arrangement, usually a full outer shell of electrons.
不同元素的原子可以通过化学键结合形成化合物。键合的类型取决于原子如何达到更稳定的电子排布，通常是填满最外层电子壳层。
Bonding occurs because unbonded atoms typically have higher energy; forming bonds lowers their overall energy and makes them more stable like the noble gases.
键合发生的原因是未成键的原子通常能量较高；形成键会降低其总能量，使它们像稀有气体一样更稳定。
2. Why Atoms Bond | 原子为何成键
Atoms bond to achieve a full outer shell of electrons, which for most atoms means 8 electrons (the octet rule). Hydrogen is an exception as it only needs 2 electrons to be stable.
原子成键是为了达到满电子外层，对大多数原子来说就是8个电子（八隅体规则）。氢是一个例外，它只需要2个电子就能稳定。
This electron arrangement resembles that of the nearest noble gas in the periodic table, providing chemical stability.
这种电子排布类似于周期表中最靠近的稀有气体，从而赋予化学稳定性。
Atoms can achieve a full outer shell by either transferring electrons or sharing electrons, leading to ionic or covalent bonding respectively.
原子可以通过转移电子或共享电子来达到满壳层，分别形成离子键或共价键。
3. Ionic Bonding: Electron Transfer | 离子键：电子转移
Ionic bonding takes place between a metal and a non-metal. Metal atoms lose electrons to form positive ions (cations), while non-metal atoms gain those electrons to form negative ions (anions).
离子键发生在金属与非金属之间。金属原子失去电子形成正离子（阳离子），而非金属原子获得这些电子形成负离子（阴离子）。
For example, in sodium chloride, each sodium atom (2,8,1) loses its one outer electron and becomes Na⁺ with an electronic configuration of 2,8. Chlorine atom (2,8,7) gains one electron to become Cl⁻ with a full outer shell of 2,8,8.
例如，在氯化钠中，每个钠原子（2,8,1）失去它的一个外层电子变成 Na⁺，电子排布为 2,8。氯原子（2,8,7）获得一个电子变成 Cl⁻，具有满壳层 2,8,8。
The oppositely charged ions are held together by strong electrostatic forces of attraction, known as ionic bonds.
带相反电荷的离子被强大的静电吸引力束缚在一起，这称为离子键。
Na → Na⁺ + e⁻ ; Cl + e⁻ → Cl⁻
4. Properties of Ionic Compounds | 离子化合物的性质
Ionic compounds have high melting and boiling points because of the strong electrostatic forces between ions in the giant lattice, which require a lot of energy to overcome.
离子化合物具有高熔点和沸点，因为巨型晶格中离子之间的静电作用力很强，需要大量能量才能克服。
They are often soluble in water but insoluble in non-polar solvents. When molten or dissolved in water, they conduct electricity because the ions are free to move and carry charge.
它们通常可溶于水，但不溶于非极性溶剂。在熔融状态或溶于水时，它们能导电，因为离子可以自由移动并携带电荷。
In the solid state, however, ionic compounds do not conduct electricity since the ions are fixed in the lattice and cannot move.
然而，固态时离子化合物不导电，因为离子被固定在晶格中无法移动。
5. Giant Ionic Lattices | 巨型离子晶格
Ionic compounds form a regular, repeating three-dimensional structure called a giant ionic lattice. This arrangement maximises the attractive forces between oppositely charged ions and minimises repulsion.
离子化合物形成规则、重复的三维结构，称为巨型离子晶格。这种排列方式使相反电荷离子间的吸引力最大化，同时尽量减少排斥力。
In sodium chloride, each Na⁺ ion is surrounded by six Cl⁻ ions, and each Cl⁻ is surrounded by six Na⁺ ions. The lattice is held together by ionic bonds extending throughout the whole crystal.
在氯化钠中，每个 Na⁺ 离子被六个 Cl⁻ 离子包围，每个 Cl⁻ 也被六个 Na⁺ 包围。整个晶体由贯穿整个结构的离子键结合。
The empirical formula of an ionic compound gives the simplest whole-number ratio of ions in the lattice, not discrete molecules.
离子化合物的化学式给出晶格中离子的最简整数比，而不是独立的分子。
6. Covalent Bonding: Electron Sharing | 共价键：电子共享
Covalent bonding occurs between non-metal atoms, where electrons are shared to achieve a full outer shell. Each shared pair of electrons forms one covalent bond.
共价键发生在非金属原子之间，通过共享电子来达到满壳层。每一对共用电子形成一个共价键。
The shared electrons are attracted to the nuclei of both atoms, holding the atoms together. In a single covalent bond, one pair of electrons is shared, as in H₂ or Cl₂.
共用电子同时被两个原子的原子核吸引，从而将原子结合在一起。在单共价键中，共用一对电子，例如 H₂ 或 Cl₂。
two or three pairs of electrons, respectively, found in molecules like O₂ (O=O) and N₂ (N≡N).
双键和三键分别涉及共享两对或三对电子，可见于 O₂（O=O）和 N₂（N≡N）等分子中。
7. Simple Molecular Substances | 简单分子物质
Many covalently bonded substances exist as simple molecules with a fixed number of atoms, such as H₂O, CO₂, and NH₃. Within the molecule, atoms are held together by strong covalent bonds.
许多共价键物质以具有固定原子数目的简单分子形式存在，例如 H₂O、CO₂ 和 NH₃。在分子内部，原子通过强共价键结合。
However, the forces between molecules (intermolecular forces) are weak, so simple molecular substances usually have low melting and boiling points.
然而，分子之间的作用力（分子间力）很弱，因此简单分子物质通常具有低熔点和沸点。
They do not conduct electricity because there are no free ions or delocalised electrons in any state.
它们不导电，因为无论处于何种状态都没有自由离子或离域电子。
8. Giant Covalent Structures | 巨型共价结构
Some covalent substances form giant covalent structures (macromolecules), where atoms are linked by covalent bonds throughout the entire structure. Examples include diamond, graphite, and silicon dioxide (SiO₂).
一些共价物质形成巨型共价结构（大分子），原子通过共价键贯穿整个结构连接。例子有金刚石、石墨和二氧化硅（SiO₂）。
Diamond has each carbon atom bonded to four other carbon atoms in a tetrahedral arrangement, making it extremely hard and giving it a very high melting point.
金刚石中每个碳原子与另外四个碳原子以四面体排列方式结合，这使它极其坚硬，熔点非常高。
In graphite, each carbon atom is bonded to three others in layers of hexagons. The fourth outer electron is delocalised, allowing graphite to conduct electricity and act as a lubricant because layers slide over each other.
石墨中，每个碳原子与另外三个碳原子结合形成六边形层。第四个外层电子离域，使石墨能够导电，并因层间滑动而起到润滑作用。
9. Comparison: Ionic vs Covalent | 比较：离子键与共价键
Ionic bonding involves electron transfer and the formation of oppositely charged ions, while covalent bonding involves electron sharing between atoms.
离子键涉及电子转移并形成带相反电荷的离子，而共价键涉及原子间的电子共享。
Ionic compounds consist of giant ionic lattices with high melting points, while simple covalent compounds have low melting points. Giant covalent substances can also have very high melting points.
离子化合物由具有高熔点的巨型离子晶格构成，而简单共价化合物熔点较低。巨型共价物质熔点也可能非常高。
Ionic substances can conduct electricity when molten or in solution, whereas most covalent substances do not conduct electricity (graphite is a notable exception).
离子物质在熔融或溶液中可以导电，而大多数共价物质不导电（石墨是一个显著的例外）。
10. Bonding and Physical Properties | 键合类型与物理性质
The type of bonding directly influences melting point, boiling point, solubility, and electrical conductivity. Understanding these property-bonding relationships is an essential skill for IGCSE exams.
键合类型直接影响熔点、沸点、溶解度和导电性。理解这些性质与键合的关系是IGCSE考试的一项核心技能。
For example, ionic compounds like MgO have very high melting points (over 2800 °C) because of strong ionic bonds, while a simple molecular substance like CH₄ melts at –182 °C due to weak intermolecular forces.
例如，像 MgO 这样的离子化合物因强离子键而熔点极高（超过2800 °C），而像 CH₄ 这样的简单分子物质因分子间力弱，熔点为 –182 °C。
Giant covalent structures such as SiO₂ have exceptionally high melting points because many covalent bonds must be broken across the entire lattice.
巨型共价结构如 SiO₂ 的熔点异常高，因为必须破坏整个晶格中的大量共价键。
11. Drawing Dot-and-Cross Diagrams | 绘制点叉图
Edexcel IGCSE exams frequently ask you to draw dot-and-cross diagrams to represent the outer shell electrons of atoms and ions. Use different symbols (dots and crosses) for electrons from different atoms.
Edexcel IGCSE 考试经常要求绘制点叉图来表示原子和离子的外层电子。用不同的符号（点和叉）表示来自不同原子的电子。
For ionic compounds, show the transfer of electrons and the resulting charges on ions. The brackets and charges are essential: [Na]⁺ and [Cl]⁻ with complete outer shells drawn.
对于离子化合物，要画出电子的转移以及离子上的电荷。括号和电荷很重要：画出[Na]⁺ 和 [Cl]⁻，并展示完整的满壳层。
For covalent molecules, show only the outer shell electrons, with shared pairs clearly marked. Example: H₂O – oxygen shares electrons with two hydrogen atoms to complete its octet.
对于共价分子，只画出外层电子，清楚地标出共用电子对。例如：H₂O – 氧与两个氢原子共享电子以完成其八隅体。
12. Summary Table | 总结表
| Property | Ionic Compounds | Simple Covalent Molecules | Giant Covalent Structures |
| Types of atoms | Metal + non-metal | Non-metal + non-metal | Non-metal atoms (C, Si) |
| Particles present | Ions | Molecules | Atoms linked by covalent bonds |
| Melting/boiling point | High | Low | Very high |
| Electrical conductivity | Only when molten or in aqueous solution | None | Graphite conducts; diamond does not |
| Structural unit | Giant ionic lattice | Small discrete molecules | Giant covalent lattice |
Published by TutorHao | IGCSE Chemistry Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图