📚 Formula & Theorem Quick Reference Handbook | 公式定理速查手册
This handbook provides a concise summary of essential chemical formulas, theorems, and rules for Year 9 Cambridge Chemistry. Use it to quickly revise key concepts and improve your problem-solving skills.
这本速查手册为你总结了Year 9剑桥化学中的核心公式、定理和规则。利用它可以快速复习关键概念，提升解题能力。
1. Atomic Structure and Electron Configuration | 原子结构与电子排布
An atom contains a tiny central nucleus made of protons and neutrons, surrounded by electrons arranged in shells. The atomic number (Z) equals the number of protons, and the mass number (A) is the sum of protons and neutrons.
原子含有一个由质子和中子构成的微小中心原子核，外面有按壳层排布的电子。原子序数(Z)等于质子数，质量数(A)是质子数与中子数之和。
Electrons fill shells in a 2, 8, 8 pattern for the first 20 elements. The first shell holds up to 2 electrons, the second and third shells up to 8 each. This arrangement determines chemical properties.
前20号元素的电子按2, 8, 8规律填充。第一壳层最多容纳2个电子，第二和第三壳层最多各容纳8个电子。这种排布决定了化学性质。
No. of neutrons = Mass number (A) − Atomic number (Z)
中子数 = 质量数(A) − 原子序数(Z)
2. Valency and Chemical Formulae | 化合价与化学式
Valency is the combining power of an element. In ionic compounds, the total positive charge must balance the total negative charge. You can use the 'swap-and-drop' method to write correct formulae.
化合价是元素的结合能力。在离子化合物中，正电荷总数必须与负电荷总数平衡。你可以用“交叉相消”法书写正确的化学式。
Common valencies: Group 1 metals are +1, Group 2 are +2, aluminium is +3, oxygen is −2, chlorine is −1. Transition metals can have variable valency, e.g. iron(II) Fe²⁺ and iron(III) Fe³⁺.
常见化合价：第1族金属为+1，第2族为+2，铝为+3，氧为−2，氯为−1。过渡金属可以有可变化合价，如铁(II) Fe²⁺ 和铁(III) Fe³⁺。
Example: Magnesium chloride → Mg²⁺ and Cl⁻ → swap valencies → MgCl₂
示例：氯化镁 → Mg²⁺ 和 Cl⁻ → 交换化合价 → MgCl₂
3. Relative Atomic Mass and Relative Molecular Mass | 相对原子质量与相对分子质量
The relative atomic mass (Aᵣ) compares the average mass of an atom of an element to 1/12 the mass of a carbon-12 atom. It has no units. The relative molecular mass (Mᵣ) is the sum of the Aᵣ values of all atoms in a molecule.
相对原子质量(Aᵣ)是将一个元素原子的平均质量与一个碳-12原子质量的1/12比较得到的，没有单位。相对分子质量(Mᵣ)是分子中所有原子的Aᵣ值之和。
To calculate Mᵣ, multiply each element's Aᵣ by the number of its atoms in the formula and add the results. This is crucial for understanding reacting masses.
计算Mᵣ时，将每种元素的Aᵣ乘以其在化学式中的原子个数，然后相加。这对理解反应物质量至关重要。
Mᵣ of H₂SO₄ = (2 × 1) + (1 × 32) + (4 × 16) = 98
H₂SO₄ 的 Mᵣ = (2 × 1) + (1 × 32) + (4 × 16) = 98
4. Writing and Balancing Chemical Equations | 化学方程式的书写与配平
ght, separated by an arrow (→). State symbols (s), (l), (g), (aq) show the physical state.
化学方程式用符号和化学式描述化学反应。反应物写在左边，生成物写在右边，中间用箭头(→)隔开。状态符号(s)、(l)、(g)、(aq)表示物理状态。
Balancing ensures the number of atoms of each element is the same on both sides, following the law of conservation of mass. Only coefficients (big numbers in front) may be changed, never subscripts.
配平确保每种元素的原子总数在两边相等，这遵循质量守恒定律。只能改变化学式前的系数，绝对不能改动下标。
Unbalanced: H₂ + O₂ → H₂O
Balanced: 2H₂ + O₂ → 2H₂O
未配平：H₂ + O₂ → H₂O
已配平：2H₂ + O₂ → 2H₂O
5. Law of Conservation of Mass | 质量守恒定律
In a chemical reaction, the total mass of the reactants equals the total mass of the products. Matter is neither created nor destroyed, only rearranged. This is a fundamental theorem in chemistry.
在化学反应中，反应物的总质量等于生成物的总质量。物质既不能被创造也不能被消灭，只能重新组合。这是化学中的一个基本定理。
In a closed system, the mass stays constant. In an open system, a mass change may appear if a gas enters or escapes, but the overall mass of all substances involved is still conserved.
在封闭体系中，质量保持不变。在开放体系中，如果有气体进入或逸出，质量可能看似改变，但所有涉及物质的总质量仍然是守恒的。
mass(reactants) = mass(products)
反应物的质量 = 生成物的质量
6. Calculating Masses in Reactions | 反应中的质量计算
Using balanced equations and relative masses, you can calculate the mass of a reactant needed or a product formed. The ratio of reacting masses is fixed and is determined by the Mᵣ and coefficients.
利用配平的方程式和相对质量，你可以计算所需反应物的质量或生成的产物质量。反应物间的质量比是固定的，由Mᵣ和配平系数决定。
tio Mg : O₂ : MgO is (2×24) : 32 : (2×40) = 48 : 32 : 80. This ratio is always maintained.
对于反应 2Mg + O₂ → 2MgO，质量比 Mg : O₂ : MgO 是 (2×24) : 32 : (2×40) = 48 : 32 : 80。这一比例始终保持不变。
mass of A / mass of B = (nA × Mᵣ_A) / (nB × Mᵣ_B)
A的质量 / B的质量 = (nA × Mᵣ_A) / (nB × Mᵣ_B)
7. Concentration of Solutions | 溶液浓度
The concentration of a solution tells you how much solute is dissolved in a given volume of solvent. It is commonly expressed in g/dm³. A more concentrated solution contains more solute per unit volume.
溶液浓度表示在一定体积的溶剂中溶解了多少溶质，常用单位是 g/dm³。浓度越高的溶液，单位体积内含有的溶质越多。
ion. When diluting a solution, the amount of solute stays the same, so mass = c₁V₁ = c₂V₂.
这个公式将溶质质量与溶液体积联系起来。稀释溶液时，溶质的总量不变，因此质量 = c₁V₁ = c₂V₂。
concentration (g/dm³) = mass of solute (g) / volume of solution (dm³)
浓度 (g/dm³) = 溶质质量 (g) / 溶液体积 (dm³)
8. pH Scale and Indicators | pH标度与指示剂
The pH scale measures the acidity or alkalinity of a solution. It ranges from 0 (strongly acidic) to 14 (strongly alkaline), with 7 being neutral. Each unit change in pH represents a ten‑fold change in H⁺ concentration.
pH标度用于衡量溶液的酸性或碱性，范围从0（强酸性）到14（强碱性），7为中性。pH每改变一个单位，H⁺浓度变化十倍。
Indicators change colour at different pH levels. Universal indicator shows a range of colours: red (pH 1-3), orange (4-5), green (6-7), blue (8-11), violet (12-14). Litmus turns red in acid and blue in alkali.
指示剂在不同pH下会变色。通用指示剂显示多种颜色：红(pH 1-3)，橙(4-5)，绿(6-7)，蓝(8-11)，紫(12-14)。石蕊试纸遇酸变红，遇碱变蓝。
pH = −log₁₀[H⁺] (advanced perspective)
pH = −log₁₀[H⁺] （进阶概念）
9. Rates of Reaction and Collision Theory | 反应速率与碰撞理论
For a reaction to occur, particles must collide with sufficient energy (activation energy) and correct orientation. The rate of reaction depends on the frequency of successful collisions.
发生化学反应需要粒子碰撞，且碰撞必须具有足够的能量（活化能）和正确的取向。反应速率取决于有效碰撞的频率。
Factors that increase the rate include: higher temperature, higher concentration of solutions, larger surface area of solids, and the use of a catalyst. A catalyst provides an alternative pathway with lower activation energy.
提高反应速率的因素包括：升高温度、增大溶液浓度、增大固体表面积和使用催化剂。催化剂能提供一条活化能更低的替代路径。
Rate ∝ collision frequency × fraction of successful collisions
速率 ∝ 碰撞频率 × 有效碰撞比例
10. States of Matter and Changes of State | 物质状态与状态变化
Matter exists as solid, liquid, or gas, depending on the arrangement and movement of particles. Melting and boiling are endothermic (energy absorbed), while freezing and condensing are exothermic (energy released).
物质以固态、液态或气态存在，取决于粒子的排列和运动。熔化和沸腾是吸热过程（吸收能量），而凝固和冷凝是放热过程（释放能量）。
During a state change, the temperature remains constant even though heating continues. The energy supplied overcomes the forces between particles rather than raising the kinetic energy.
在状态变化过程中，即使持续加热温度也保持不变。此时提供的能量用于克服粒子间的吸引力，而不是增加动能。
energy = mass × specific latent heat (advanced)
能量 = 质量 × 比潜热 （进阶）
11. Periodic Table and Group Trends | 元素周期表与族趋势
Elements are arranged in order of increasing atomic number. The vertical columns are called groups; elements in the same group have similar chemical properties because they have the same number of outer electrons.
元素按原子序数递增的顺序排列。纵列称为族；同族元素化学性质相似，因为它们的最外层电子数相同。
Group 1 (alkali metals) are soft, reactive metals that form +1 ions. Group 7 (halogens) are diatomic non‑metals that form −1 ions. Group 8 (noble gases) are unreactive monatomic gases with full outer shells.
第1族（碱金属）是质软、活泼的金属，形成+1价离子。第7族（卤素）是双原子非金属，形成−1价离子。第8族（稀有气体）是具有稳定最外层的单原子气体，很不活泼。
Reactivity increases down Group 1 but decreases down Group 7.
第1族自上而下活泼性增强，第7族自上而下活泼性减弱。
12. Energy Changes in Reactions | 反应中的能量变化
Chemical reactions either release energy to the surroundings (exothermic, ΔH negative) or absorb energy (endothermic, ΔH positive). Bond breaking is endothermic, bond making is exothermic.
化学反应要么向环境释放能量（放热反应，ΔH为负），要么吸收能量（吸热反应，ΔH为正）。断键吸热，成键放热。
In an exothermic reaction, the energy released by forming new bonds is greater than the energy needed to break old bonds, resulting in a temperature rise. Combustion and neutralisation are exothermic.
在放热反应中，形成新键释放的能量大于断裂旧键所需的能量，导致温度升高。燃烧和中和反应都是放热反应。
Overall energy change = energy in (bond breaking) − energy out (bond making)
总能量变化 = 吸收能量（断键）− 放出能量（成键）
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