📚 Core Theory for CAIE IGCSE Chemistry 0620 | CAIE IGCSE 化学 0620 核心理论
This article summarises the essential theory topics in the CAIE IGCSE Chemistry 0620 syllabus. It is designed to help you revise key definitions, patterns and calculations before the examination, moving from atomic structure and bonding through quantitative chemistry, energetics, rates, acids and salts, electrolysis and organic chemistry.
本文总结 CAIE IGCSE 化学 0620 课程的核心理论主题，旨在帮助你复习关键定义、规律和计算，为考试做好准备。内容从原子结构与化学键出发，逐步覆盖定量化学、能量变化、反应速率、酸碱盐、电解以及有机化学。
Every examination question is built on a small number of underlying ideas: particles and their arrangement, the transfer or sharing of electrons, the conservation of mass and energy, and the relationship between structure and properties. If you can explain these ideas clearly and use the correct terminology and units, you can answer almost any structured or extended-response question.
每一道考题都建立在少数几个底层概念之上：粒子及其排列方式、电子的转移或共用、质量与能量的守恒，以及结构与性质之间的关系。如果你能清楚地解释这些概念，并使用正确的术语和单位，就几乎可以应对任何结构化题或论述题。
1. Atomic Structure and Isotopes | 原子结构与同位素
An atom consists of a central nucleus containing protons and neutrons, surrounded by electrons arranged in shells. Protons carry a positive charge, electrons carry a negative charge, and neutrons are neutral. The proton number (atomic number) determines the element, while the nucleon number (mass number) equals the total number of protons plus neutrons.
原子由含质子和中子的中心原子核以及按电子层排列的核外电子组成。质子带正电荷，电子带负电荷，中子不带电。质子数（原子序数）决定元素种类，而核子数（质量数）等于质子数与中子数之和。
Most of the mass of an atom is concentrated in the nucleus, but most of the volume is empty space occupied by the electron shells.
原子的质量几乎全部集中在原子核，但原子的大部分体积是电子层所占的空隙。
In a neutral atom, the number of electrons equals the number of protons, so the overall charge is zero.
在中性原子中，电子数等于质子数，因此整体电荷为零。
The number of neutrons is found from: neutrons = nucleon number − proton number.
中子数可由下式求出：中子数 = 核子数 − 质子数。
Isotopes are atoms of the same element with the same proton number but different nucleon numbers. They have identical chemical properties because they have the same number of outer-shell electrons, but different physical properties such as mass and density.
同位素是同一元素中质子数相同但核子数不同的原子。它们的化学性质相同，因为外层电子数相同，但质量、密度等物理性质不同。
Isotopes are used in medicine and industry, for example radioactive isotopes for cancer treatment and carbon-14 for dating archaeological remains. The relative atomic mass of an element is the weighted average of its isotopes.
同位素在医学和工业中有广泛用途，例如用放射性同位素治疗癌症，用碳-14 测定考古遗存年代。元素的相对原子质量是其各同位素质量的加权平均值。
Relative atomic mass Aᵣ = (Σ isotope mass × percentage abundance) ÷ 100
相对原子质量 Aᵣ = (Σ 同位素质量 × 百分丰度) ÷ 100
Electrons occupy shells with maximum capacities of 2, 8, 8 for the first three shells in IGCSE. The electronic configuration controls the element's group and period in the Periodic Table.
电子占据电子层，IGCSE 阶段前三层最多容纳 2、8、8 个电子。电子排布决定元素在周期表中的族和周期。
2. Electronic Configuration and the Periodic Table | 电子排布与周期表
The Periodic Table arranges elements in order of increasing proton number. Elements in the same group have the same number of outer-shell electrons, so they show similar chemical properties and form compounds with similar formulae.
周期表按质子数递增排列元素。同一族元素的外层电子数相同，因此化学性质相似，形成的化合物化学式也相似。
Group number = number of outer-shell electrons (for Groups I to VII).
族序数 = 最外层电子数（第 I 族至第 VII 族）。
Period number = number of occupied electron shells.
周期序数 = 已占据的电子层数。
Metals are found on the left and in the centre; non-metals are on the right and top-right.
金属位于左侧和中部；非金属位于右侧和右上角。
Moving down Group I, the alkali metals become more reactive because the outer electron is further from the nucleus and is lost more easily. Moving down Group VII, the halogens become less reactive for the same reason, and their melting and boiling points increase.
沿第 I 族向下，碱金属活泼性增强，因为最外层电子离核更远、更易失去。沿第 VII 族向下，卤素活泼性减弱，原因相同，而其熔点和沸点升高。
Group 0 contains the noble gases, which are unreactive because they have full outer shells. The transition metals in the centre are harder, denser and have higher melting points than Group I metals, and they often form coloured compounds and act as catalysts.
第 0 族为稀有气体，因其最外层已满而性质不活泼。中部的过渡金属比第 I 族金属更硬、密度更大、熔点更高，且常形成有色化合物并用作催化剂。
3. Ionic Bonding and Giant Ionic Lattices | 离子键与巨型离子晶格
Ionic bonding occurs when a metal atom transfers one or more electrons to a non-metal atom. The metal forms a positive cation, and the non-metal forms a negative anion. Oppositely charged ions attract each other strongly in a giant ionic lattice.
当金属原子将一个或多个电子转移给非金属原子时形成离子键。金属形成带正电的阳离子，非金属形成带负电的阴离子。带相反电荷的离子在巨型离子晶格中强烈相互吸引。
The charge on an ion can be predicted from its position in the Periodic Table. Group I metals form 1+ ions, Group II metals form 2+ ions, Group VI non-metals form 2− ions, and Group VII non-metals form 1− ions.
离子的电荷可由元素在周期表中的位置预测。第 I 族金属形成 1+ 离子，第 II 族金属形成 2+ 离子，第 VI 族非金属形成 2− 离子，第 VII 族非金属形成 1− 离子。
Example: Na → Na⁺ + e⁻ ; Cl + e⁻ → Cl⁻ ; Na⁺ + Cl⁻ → NaCl
示例：Na → Na⁺ + e⁻ ；Cl + e⁻ → Cl⁻ ；Na⁺ + Cl⁻ → NaCl
Because the electrostatic forces in a giant ionic lattice are strong in all directions, ionic compounds have high melting and boiling points. They do not conduct electricity when solid because the ions are fixed in position, but they do conduct when molten or dissolved in water because the ions become free to move.
由于巨型离子晶格中的静电引力在各个方向都很强，离子化合物具有高熔点和沸点。固态时不导电，因为离子被固定在晶格中；熔融或溶于水时导电，因为离子可以自由移动。
Most ionic compounds are soluble in water. When writing formulae, the total positive charge must balance the total negative charge, for example MgCl₂, Na₂O and Al₂O₃.
大多数离子化合物可溶于水。书写化学式时，正电荷总数必须与负电荷总数相等，例如 MgCl₂、Na₂O 和 Al₂O₃。
4. Covalent Bonding and Giant Covalent Structures | 共价键与巨型共价结构
A covalent bond is formed when two non-metal atoms share a pair of electrons, so that both atoms achieve a full outer shell. Each shared pair is one covalent bond, shown as a single line in a displayed formula.
共价键由两个非金属原子共用一对电子形成，使两个原子都达到满外层。每一对共用电子代表一个共价键，在展开式中用一条短线表示。
Simple molecular substances such as H₂, Cl₂, CH₄, CO₂ and H₂O have weak intermolecular forces between molecules. Only a small amount of energy is needed to overcome these forces, so they have low melting and boiling points and are usually gases or volatile liquids at room temperature.
H₂、Cl₂、CH₄、CO₂、H₂O 等简单分子物质，分子之间只有微弱的分子间作用力。克服这些力所需能量很小，因此它们的熔点和沸点低，常温下通常是气体或易挥发的液体。
Simple molecular substances do not conduct electricity, because their molecules are uncharged and there are no free ions or electrons. The covalent bonds within a molecule are strong, but it is the weak forces between molecules that break when the substance melts or boils.
简单分子物质不导电，因为分子不带电，也没有自由离子或电子。分子内的共价键很强，但熔化或沸腾时被破坏的是分子间的弱作用力。
Giant covalent structures have a network of strong covalent bonds throughout the whole substance. Diamond, graphite and silicon dioxide are typical examples and all have very high melting points.
巨型共价结构在整个物质中由强共价键构成网状结构，金刚石、石墨和二氧化硅是典型例子，它们都有很高的熔点。
Diamond: each carbon atom bonds to four others in a rigid tetrahedral network - very hard, used in cutting tools, does not conduct.
金刚石：每个碳原子与另外四个碳原子形成刚性四面体网络，非常坚硬，用于切割工具，不导电。
Graphite: each carbon atom bonds to three others in layers, with one delocalised electron per atom - soft, slippery, and a good conductor.
石墨：每个碳原子与另外三个碳原子成层状结构，每个原子有一个离域电子，因此质软、滑腻且导电性良好。
Silicon dioxide: a similar tetrahedral network to diamond, very high melting point, used in glass making.
二氧化硅：与金刚石类似的四面体网络，熔点很高，用于制造玻璃。
5. Metallic Bonding and Structure-Property Links | 金属键与结构与性质
Metallic bonding consists of a lattice of positive ions surrounded by a sea of delocalised electrons. The attraction between the positive ions and the delocalised electrons holds the structure together.
金属键由正离子晶格和包围其间的离域电子海组成。正离子与离域电子之间的吸引力把整个结构维系在一起。
Because the delocalised electrons are free to move, metals conduct electricity and heat well. Because the layers of positive ions can slide over one another without breaking the bonding, metals are malleable and ductile.
由于离域电子可以自由移动，金属具有良好的导电和导热性。由于正离子层之间可以相互滑动而不破坏金属键，金属具有延展性和可塑性。
Metals generally have high melting and boiling points because a large amount of energy is needed to overcome the strong metallic bonds. Melting points increase across a period and decrease down a group as the ions become larger and the bonding weaker.
金属通常具有高熔点和沸点，因为破坏强金属键需要大量能量。同周期从左到右熔点一般升高，同族向下离子半径增大、金属键减弱，熔点降低。
| Structure | Particles | Melting point | Conducts? |
| Giant ionic | Ions | High | Only molten or aqueous |
| Simple molecular | Molecules | Low | No |
| Giant covalent | Atoms | Very high | Only graphite |
| Giant metallic | Ions and electrons | High (varies) | Yes |
6. Chemical Formulae, Equations and the Mole | 化学式、方程式与摩尔
A chemical equation must be balanced so that the number of atoms of each element is the same on both sides. This follows from the law of conservation of mass: atoms are neither created nor destroyed in a chemical reaction.
化学方程式必须配平，使两边每种元素的原子数目相等。这是由质量守恒定律决定的：化学反应中原子既不会被创造，也不会被消灭。
State symbols are added to show the physical state of each substance: (s) for solid, (l) for liquid, (g) for gas and (aq) for aqueous solution.
方程式应加上状态符号以表示各物质的物理状态：(s) 表示固体，(l) 表示液体，(g) 表示气体，(aq) 表示水溶液。
Example: 2H₂ + O₂ → 2H₂O ; CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂
示例：2H₂ + O₂ → 2H₂O ；CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂
n as the Avogadro constant. The relative formula mass Mᵣ of a compound is the sum of the relative atomic masses of all the atoms shown in its formula.
摩尔是含有 6.02 × 10²³ 个粒子的物质的量，该数值称为阿伏加德罗常数。化合物的相对式量 Mᵣ 等于其化学式中所有原子相对原子质量的总和。
moles n = mass m ÷ relative formula mass Mᵣ
物质的量 n = 质量 m ÷ 相对式量 Mᵣ
In calculations, always convert the given mass into moles first, use the mole ratio from the balanced equation, then convert back into the required mass, volume or concentration. Remember that percentage composition by mass can also be calculated from the formula.
计算时，先把已知质量换算成物质的量，再利用配平方程式的摩尔比，最后换算回所求的质量、体积或浓度。此外，还可以根据化学式计算质量百分组成。
7. Quantitative Chemistry: Concentration, Gas Volumes and Yield | 定量化学：浓度、气体体积与产率
The concentration of a solution is the amount of solute dissolved in a given volume of solution. It is usually expressed in mol/dm³ or g/dm³, and the volume must be converted from cm³ to dm³ by dividing by 1000.
溶液的浓度是溶质溶解在一定体积溶液中的量，通常用 mol/dm³ 或 g/dm³ 表示。计算时体积需由 cm³ 除以 1000 换算为 dm³。
concentration (mol/dm³) = moles of solute ÷ volume of solution (dm³)
浓度 (mol/dm³) = 溶质的物质的量 ÷ 溶液体积 (dm³)
For gases, one mole of any gas occupies 24 dm³ at room temperature and pressure. This allows the volume of gas produced or used in a reaction to be calculated directly from the moles.
对于气体，在室温常压下 1 摩尔任何气体都占据 24 dm³。由此可直接由物质的量计算反应中生成或消耗的气体体积。
moles of gas = volume of gas (dm³) ÷ 24 dm³
气体的物质的量 = 气体体积 (dm³) ÷ 24 dm³
The limiting reactant is the reactant that is used up first and therefore determines the amount of product formed. Percentage yield compares the actual mass of product obtained with the theoretical maximum, while atom economy compares the mass of the desired product with the total mass of all products.
限量试剂是最先被消耗完的反应物，它决定了生成物的量。产率把实际得到的产物质量与理论最大值进行比较，而原子经济性把目标产物的质量与所有产物的总质量进行比较。
percentage yield = (actual mass ÷ theoretical mass) × 100%
产率 = (实际质量 ÷ 理论质量) × 100%
8. Energetics: Energy Changes in Reactions | 能量变化：化学反应中的能量
Chemical reactions involve energy changes. An exothermic reaction releases energy to the surroundings, so the temperature rises, and the enthalpy change ΔH is negative. Combustion, neutralisation and respiration are exothermic.
化学反应伴随能量变化。放热反应向环境释放能量，温度升高，焓变 ΔH 为负值。燃烧、中和和呼吸作用都是放热反应。
An endothermic reaction takes in energy from the surroundings, so the temperature falls, and ΔH is positive. Thermal decomposition, photosynthesis and the dissolving of ammonium nitrate are endothermic.
吸热反应从环境吸收能量，温度下降，ΔH 为正值。热分解、光合作用以及硝酸铵的溶解都是吸热反应。
Energy changes can be explained using bond energies. Breaking bonds requires energy (endothermic), while forming bonds releases energy (exothermic). The overall energy change depends on the balance between the two.
能量变化可用键能解释。断键需要吸收能量（吸热），成键会释放能量（放热）。总能量变化取决于两者之间的差值。
ΔH = energy absorbed to break bonds − energy released when bonds form
ΔH = 断键吸收的能量 − 成键释放的能量
Energy level diagrams are used to show these changes: in an exothermic reaction the products are lower in energy than the reactants, and in an endothermic reaction the products are higher. The difference between the reactant level and the top of the curve is the activation energy.
能量图可用来表示这些变化：放热反应中生成物的能量低于反应物，吸热反应中生成物的能量高于反应物。反应物能量与曲线最高点之差即为活化能。
9. Rates of Reaction and Reversible Reactions | 反应速率与可逆反应
The rate of a reaction is the speed at which reactants are used up or products are formed. It can be measured by the loss in mass, the volume of gas produced, or the time taken for a colour change or precipitate to appear.
反应速率是反应物被消耗或生成物生成的快慢。可通过质量减少、生成气体体积，或出现颜色变化、沉淀所需时间来测定。
According to collision theory, particles must collide with sufficient energy for a reaction to occur. The minimum energy required is the activation energy, and only collisions that exceed this energy are successful.
根据碰撞理论，粒子必须以足够的能量碰撞才能发生反应。所需的最低能量称为活化能，只有能量超过活化能的碰撞才有效。
Increasing concentration or pressure increases the frequency of collisions.
增大浓度或压强会增加碰撞频率。
Increasing temperature increases both the frequency and the energy of collisions.
升高温度同时增加碰撞频率和碰撞能量。
Increasing surface area of a solid exposes more particles to collision.
增大固体的表面积可让更多粒子参与碰撞。
A catalyst provides an alternative pathway with a lower activation energy.
催化剂提供一条活化能更低的替代反应路径。
Some reactions are reversible, shown by the symbol ⇌. When the rate of the forward reaction equals the rate of the backward reaction and the concentrations remain constant, the system is in dynamic equilibrium.
有些反应是可逆的，用符号 ⇌ 表示。当正反应速率等于逆反应速率且各物质浓度保持不变时，体系处于动态平衡。
Changing conditions shifts the position of equilibrium. Increasing temperature favours the endothermic direction, increasing pressure favours the side with fewer gas molecules, and adding a catalyst only speeds up the attainment of equilibrium without changing its position.
改变条件会使平衡移动。升高温度有利于吸热方向，增大压强有利于气体分子数较少的一侧，而加入催化剂只加快达到平衡的速率，不改变平衡位置。
10. Acids, Bases, Salts and Chemical Tests | 酸、碱、盐与化学检验
An acid is a proton donor that produces H⁺ ions in water, and a base is a proton acceptor. An alkali is a soluble base that produces OH⁻ ions in water. The pH scale runs from 0 to 14, with values below 7 acidic, 7 neutral and above 7 alkaline.
酸是在水中产生 H⁺ 离子的质子给予体，碱是质子接受体。可溶性碱称为碱，在水中产生 OH⁻ 离子。pH 范围由 0 到 14，小于 7 为酸性，等于 7 为中性，大于 7 为碱性。
Neutralisation is the reaction between an acid and a base to form a salt and water. The ionic equation is always the same for strong acids and alkalis in solution.
中和反应是酸与碱反应生成盐和水。对于溶液中的强酸和强碱，其离子方程式总是相同的。
H⁺ + OH⁻ → H₂O ; acid + metal → salt + hydrogen ; acid + carbonate → salt + water + CO₂
H⁺ + OH⁻ → H₂O ；酸 + 金属 → 盐 + 氢气 ；酸 + 碳酸盐 → 盐 + 水 + 二氧化碳
Soluble salts can be prepared by titration using an indicator to find the exact volume needed for neutralisation.
可溶性盐可用滴定法制备，用指示剂确定恰好中和所需的体积。
Insoluble salts are prepared by precipitation, mixing two solutions so that the insoluble salt forms and is filtered off.
难溶性盐可用沉淀法制备，将两种溶液混合使难溶盐析出后过滤。
Excess metal oxide or carbonate is added to acid, then filtered off and the solution crystallised.
也可向酸中加入过量的金属氧化物或碳酸盐，过滤后蒸发结晶。
Common tests include: hydrogen gives a squeaky pop with a lighted splint, oxygen relights a glowing splint, carbon dioxide turns limewater milky, chlorine bleaches damp litmus paper, and ammonia turns damp red litmus paper blue. Flame tests identify metal ions such as Li⁺ (red), Na⁺ (yellow), K⁺ (lilac), Ca²⁺ (orange-red) and Cu²⁺ (blue-green).
常见气体检验：氢气遇点燃的木条发出爆鸣声，
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