📚 Year 12 WJEC Chemistry: Core Knowledge Recap | Year 12 WJEC 化学：核心知识点梳理
The Year 12 WJEC Chemistry specification builds the essential foundation for advanced study. Topics span atomic structure, bonding, mole calculations, energetics, kinetics, equilibria, organic reactions, and analytical techniques. A solid grasp of these core ideas is crucial for exam success and progression into Year 13 topics.
Year 12 WJEC 化学课程建立了进阶学习的必要基础。主题涵盖原子结构、化学键、摩尔计算、能量学、动力学、平衡、有机反应以及分析技术。扎实掌握这些核心概念对于考试成功和顺利进入 Year 13 的学习至关重要。
1. Atomic Structure and the Periodic Table | 原子结构及周期表
Atoms consist of a nucleus containing protons and neutrons, surrounded by electrons arranged in energy levels or shells.
原子由包含质子和中子的原子核，以及排布在能级或电子层中的电子组成。
The atomic number (Z) gives the number of protons, while the mass number (A) is the sum of protons and neutrons.
原子序数 (Z) 表示质子数，质量数 (A) 是质子数与中子数之和。
Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons; relative atomic mass is the weighted average of isotopic masses relative to 1/12th of ¹²C.
同位素是同一元素中质子数相同而中子数不同的原子；相对原子质量是各同位素质量以 ¹²C 的 1/12 为标准的加权平均值。
Electrons occupy orbitals in a specific order: 1s, 2s, 2p, 3s, 3p, 4s, 3d, following the Aufbau principle. Electron configurations determine chemical properties.
电子按照构造原理填充轨道，顺序为：1s, 2s, 2p, 3s, 3p, 4s, 3d。电子构型决定着化学性质。
The first ionisation energy is the energy required to remove one mole of electrons from one mole of gaseous atoms. It increases across a period due to greater nuclear charge, and decreases down a group because of increased shielding and atomic radius.
第一电离能是从一摩尔气态原子中移去一摩尔电子所需的能量。由于核电荷增加，它沿周期从左到右递增；由于屏蔽效应增强和原子半径增大，它沿族自上而下递减。
2. Bonding, Structure, and Intermolecular Forces | 化学键、结构与分子间作用力
Ionic bonding involves electrostatic attraction between oppositely charged ions, typically forming giant ionic lattices with high melting points and electrical conductivity when molten.
离子键是带相反电荷离子间的静电吸引力，通常形成巨型离子晶格，熔点高，熔融态可导电。
Covalent bonding is the sharing of electron pairs between atoms. It can lead to simple molecular structures (low melting points, no conductivity) or giant covalent networks such as diamond and silicon dioxide, which are very hard and have high melting points.
共价键是原子间共用电子对。可形成简单分子结构（熔点低，不导电）或巨型共价网络，如金刚石和二氧化硅，它们极硬且熔点极高。
Metallic bonding is the attraction between delocalised electrons and positive metal ions, giving metals their malleability, high conductivity, and lustre.
金属键是离域电子与正金属离子间的吸引作用，赋予了金属延展性、高导电性和光泽。
Electronegativity is the ability of an atom to attract the bonding pair of electrons. Unequal sharing leads to polar bonds and, when asymmetric, permanent molecular dipoles.
电负性是原子吸引成键电子对的能力。不均衡的共用导致极性键，分子不对称时还会产生永久偶极。
Intermolecular forces include London (dispersion) forces present in all molecules, permanent dipole–dipole interactions in polar molecules, and hydrogen bonding when H is attached to N, O, or F. Hydrogen bonds are the strongest of these and greatly influence physical properties like boiling points.
分子间作用力包括所有分子中都存在的伦敦力（色散力）、极性分子间的永久偶极–偶极作用，以及当 H 与 N、O 或 F 相连时形成的氢键。氢键是其中最强的，显著影响沸点等物理性质。
3. The Mole, Stoichiometry, and Titrations | 摩尔、化学计量与滴定
The mole is the unit of amount of substance; one mole contains 6.022 × 10²³ entities. The formula n = m / M relates mass (g), molar mass (g mol⁻¹), and amount (mol).
摩尔是物质的量的单位；一摩尔包含 6.022 × 10²³ 个实体。公式 n = m / M 将质量 (g)、摩尔质量 (g mol⁻¹) 和物质的量 (mol) 关联起来。
n = m / M
In solution, concentration c = n / V, where V is measured in dm³. Dilutions and titrations rely on accurate volumetric measurements using a pipette and burette.
在溶液中，浓度 c = n / V，其中 V 的单位为 dm³。稀释和滴定依赖于用移液管和滴定管进行的精确体积测量。
Titration calculations use the mole ratio from a balanced equation to determine unknown concentrations. Common indicators like phenolphthalein or methyl orange signal the end point.
滴定计算利用平衡方程式中的摩尔比来求出未知浓度。酚酞或甲基橙等常用指示剂指示终点。
Percentage yield compares actual yield to theoretical yield, while atom economy evaluates how efficiently reactant atoms are incorporated into the desired product.
百分产率将实际产量与理论产量相比较，而原子经济性则评估反应物原子被纳入目标产品的效率。
4. Acids and Bases: Bronsted–Lowry Theory and pH | 酸与碱：布朗斯特–劳里理论与 pH
A Bronsted–Lowry acid is a proton (H⁺) donor; a base is a proton acceptor. When an acid donates a proton, it forms its conjugate base.
布朗斯特–劳里酸是质子 (H⁺) 的给体；碱是质子的受体。酸给出质子后形成其共轭碱。
Strong acids, such as HCl and H₂SO₄, dissociate completely in water, making [H⁺] equal to the initial acid concentration (for monoprotic acids).
强酸（如 HCl 和 H₂SO₄）在水中完全离解，因此（对于一元酸）[H⁺] 等于酸的初始浓度。
pH is defined as the negative logarithm of the hydrogen ion concentration: pH = –log[H⁺]. For strong monoprotic acids, pH can be calculated directly from concentration.
pH 定义为氢离子浓度的负对数：pH = –log[H⁺]。对于一元强酸，可以直接根据浓度计算 pH。
pH = –log₁₀[H⁺]
Titration curves show how pH changes as a base is added to an acid. The equivalence point for a strong acid–strong base titration occurs at pH 7; choice of indicator depends on the sharp pH change around the endpoint.
滴定曲线显示碱加入酸时 pH 如何变化。强酸–强碱滴定的等当点位于 pH 7；指示剂的选择取决于终点附近 pH 的突跃范围。
5. Redox Chemistry and Oxidation States | 氧化还原化学与氧化态
Oxidation is loss of electrons; reduction is gain of electrons. A redox reaction involves both processes occurring simultaneously.
氧化是失去电子，还原是获得电子。氧化还原反应中这两种过程同时发生。
Oxidation states (numbers) are assigned using rules: free elements are 0, monatomic ions have the charge as oxidation state, oxygen is usually –2, and hydrogen is +1. The sum of oxidation states in a compound equals the overall charge.
氧化态（氧化数）按照规则指定：游离元素为 0，单原子离子的氧化数等于其电荷数，氧通常为 –2，氢为 +1。化合物中氧化数的代数和等于总电荷。
In a redox equation, half-equations can be written to show the electron transfer separately. The species that is oxidised acts as a reducing agent, and the species reduced acts as an oxidising agent.
在氧化还原方程中，可以分别写出半反应式来展示电子转移。被氧化的物质充当还原剂，被还原的物质充当氧化剂。
Example: Mg + Cu²⁺ → Mg²⁺ + Cu. Mg is oxidised (oxidation state from 0 to +2), Cu²⁺ is reduced (from +2 to 0).
示例：Mg + Cu²⁺ → Mg²⁺ + Cu。Mg 被氧化（氧化数从 0 升至 +2），Cu²⁺ 被还原（从 +2 降至 0）。
6. Energetics: Enthalpy Changes and Hess’s Law | 能量学：焓变及赫斯定律
Enthalpy change (ΔH) is the heat energy change at constant pressure. Exothermic reactions release heat (ΔH negative); endothermic reactions absorb heat (ΔH positive).
焓变 (ΔH) 是恒压条件下的热量变化。放热反应释放热量（ΔH 为负）；吸热反应吸收热量（ΔH 为正）。
The heat change in solution can be measured using q = mcΔT, where m is mass, c is specific heat capacity, and ΔT is the temperature change. Then ΔH = –q / n to account for the number of moles.
溶液中的热量变化可用 q = mcΔT 来量度，其中 m 为质量，c 为比热容，ΔT 为温度变化。再通过 ΔH = –q / n 换算成每摩尔反应的热效应。
q = mcΔT
Hess’s Law states that the total enthalpy change for a reaction is independent of the route taken. Enthalpy cycles using standard enthalpies of combustion or formation are used to calculate unknown ΔH values.
赫斯定律指出，反应的总焓变与所取的路径无关。利用标准燃烧焓或标准生成焓构建的焓循环可用于计算未知的 ΔH 值。
Bond enthalpy calculations also estimate ΔH through Σ (bonds broken) – Σ (bonds formed).
通过键能计算，ΔH ≈ Σ (断裂的键能) – Σ (生成的键能)，也可估算反应热。
7. Kinetics: Collision Theory and Reaction Rates | 动力学：碰撞理论与反应速率
For a reaction to occur, particles must collide with sufficient energy (at least the activation energy, Ea) and with the correct orientation.
反应的发生要求粒子间发生碰撞，且碰撞能量至少达到活化能 (Ea)，同时碰撞取向要合适。
The rate of reaction increases when the concentration of reactants rises, because there are more frequent collisions per unit time.
反应物浓度升高会使反应速率加快，因为单位时间内的碰撞频率增加。
Increasing temperature gives particles greater kinetic energy, so a larger proportion of collisions exceed Ea, as shown by the Maxwell–Boltzmann distribution.
温度升高使粒子动能增大，因此超出 Ea 的碰撞比例上升，这可由麦克斯韦–玻尔兹曼分布解释。
A catalyst provides an alternative reaction pathway with a lower activation energy. It remains chemically unchanged at the end of the reaction and does not affect the equilibrium position.
催化剂提供一条活化能较低的反应途径。在反应结束时其化学性质保持不变，且不影响平衡位置。
8. Chemical Equilibria and Le Chatelier’s Principle | 化学平衡与勒夏特列原理
Many reactions are reversible, indicated by the symbol ⇌. At equilibrium, the rate of the forward reaction equals the rate of the backward reaction, and the concentrations of reactants and products remain constant.
许多反应是可逆的，用符号 ⇌ 表示。达到平衡时，正反应速率与逆反应速率相等，各物质浓度保持恒定。
The equilibrium constant Kc is expressed in terms of concentrations for a homogeneous system: for the reaction aA + bB ⇌ cC + dD,
平衡常数 Kc 用于均相体系，以浓度表示：对于反应 aA + bB ⇌ cC + dD，
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