📚 Year 8 Cambridge Chemistry Formula & Theorem Quick Reference Handbook | 八年级剑桥化学公式定理速查手册
This handy quick reference handbook pulls together the essential formulas, definitions and key theorems for Year 8 Cambridge Chemistry. Mastering these building blocks will give you confidence when calculating relative masses, mass ratios, concentrations, and interpreting chemical equations. Keep this guide close for revision and homework help.
这本便捷的速查手册汇集了八年级剑桥化学的核心公式、定义和关键定理。掌握这些基础模块，你将能自信地计算相对质量、质量比、浓度，并理解化学方程式。在复习和做作业时，不妨随时查阅。
1. Atomic Structure and Symbols | 原子结构与符号
All matter is made of atoms. Each atom has a tiny, dense nucleus containing protons (positive charge) and neutrons (no charge), surrounded by electrons (negative charge) that move around the nucleus in shells.
所有物质都由原子构成。每个原子都有一个极小且致密的原子核，内含带正电的质子和不带电的中子，原子核外有带负电的电子，它们在电子层中运动。
The atomic number (Z) is the number of protons in the nucleus. In a neutral atom, the number of protons equals the number of electrons, so the atom has no overall charge.
原子序数（Z）是原子核内的质子数。在中性原子中，质子数等于电子数，因此原子整体不显电性。
The mass number (A) is the total number of protons and neutrons in the nucleus. It is always a whole number.
质量数（A）是原子核内质子数与中子数的总和，它总是整数。
Atomic number Z = number of protons = number of electrons (in a neutral atom)
原子序数 Z = 质子数 = 电子数（中性原子中）
Mass number A = number of protons + number of neutrons → A = Z + N
质量数 A = 质子数 + 中子数 → A = Z + N
An element's chemical symbol, such as O for oxygen or Na for sodium, represents one atom of that element. The full symbol notation often shows the mass number at the top left and the atomic number at the bottom left, e.g. ²³Na₁₁ (where 23 is A, 11 is Z).
元素的化学符号，例如 O 代表氧、Na 代表钠，表示该元素的一个原子。完整的符号标记通常将质量数写在左上角，原子序数写在左下角，如 ²³Na₁₁（其中 23 为 A，11 为 Z）。
2. Relative Atomic Mass and Relative Formula Mass | 相对原子质量与相对式量
The relative atomic mass (Ar) is the average mass of an atom of an element compared to 1/12 of the mass of a carbon‑12 atom. Ar has no units because it is a ratio.
相对原子质量（Ar）是一个元素原子的平均质量与一个碳‑12 原子质量的 1/12 的比值。Ar 是比值，因此没有单位。
For molecules and giant structures, we use the relative formula mass (Mr). It is the sum of the relative atomic masses of all the atoms shown in the chemical formula.
对于分子和巨型结构，我们使用相对式量（Mr）。它是化学式中所有原子的相对原子质量之和。
Mr = Σ Ar (sum of the Ar values for each atom in the formula)
Mr = Σ Ar （化学式中各原子 Ar 值的总和）
Example: Water, H₂O. Ar of H = 1, Ar of O = 16. Mr (H₂O) = (2 × 1) + 16 = 18.
示例：水 H₂O。Ar(H) = 1，Ar(O) = 16。Mr (H₂O) = (2 × 1) + 16 = 18。
atoms shown by the subscript. For calcium carbonate CaCO₃: Mr = 40 + 12 + (3 × 16) = 100.
需要根据下标所示的原子个数乘以 Ar 进行计算。如碳酸钙 CaCO₃：Mr = 40 + 12 + (3 × 16) = 100。
3. Mass Ratios and Percentage Composition in Compounds | 化合物中的质量比与百分比组成
From a chemical formula you can find the mass ratio in which elements are combined. Write the total mass of each element using Ar values, then simplify the ratio to whole numbers.
从化学式可以求出元素化合的质量比。利用 Ar 值计算每种元素的总质量，再将比例化简为最简整数比。
For magnesium oxide MgO: Mg (24) and O (16). The mass ratio Mg : O = 24 : 16 = 3 : 2.
氧化镁 MgO：Mg(24) 与 O(16)，质量比 Mg : O = 24 : 16 = 3 : 2。
The percentage by mass of an element in a compound is given by the formula below. This tells you what fraction of the total mass comes from that element.
化合物中某元素的质量百分数由以下公式给出，它告诉你该元素占总质量的比例。
Percentage of element = (total Ar of the element in the formula ÷ Mr) × 100%
元素的质量分数 = （化学式中该元素的 Ar 总和 ÷ Mr）× 100%
For water H₂O: % H = (2/18) × 100% = 11.1%; % O = (16/18) × 100% = 88.9%.
以水 H₂O 为例：H% = (2/18) × 100% = 11.1%；O% = (16/18) × 100% = 88.9%。
4. Conservation of Mass and Balancing Equations | 质量守恒与化学方程式配平
The law of conservation of mass states that the total mass of reactants equals the total mass of products in a chemical reaction. Atoms are rearranged, not created or destroyed.
质量守恒定律指出，化学反应中反应物的总质量等于生成物的总质量。原子只是重新排列，既未创生也未毁灭。
Therefore, a chemical equation must be balanced. The number of atoms of each element must be the same on both sides of the arrow.
因此，化学方程式必须配平。方程两侧每种元素的原子总数必须相等。
Steps to balance: Write the word equation. Replace words with correct formulas. Count atoms on each side. Add large coefficients (never change the small subscripts inside formulas) to balance the atoms one by one.
配平步骤：写出文字表达式。用正确的化学式代替物质名称。数出两侧每种原子个数。通过添加化学式前的大系数（切勿更改化学式内的小下标）逐个配平原子。
Example: H₂ + O₂ → H₂O. Balance: 2 H₂ + O₂ → 2 H₂O. Now 4 H and 2 O on each side.
示例：H₂ + O₂ → H₂O。配平后：2 H₂ + O₂ → 2 H₂O，两侧均为 4 个 H 和 2 个 O。
The physical state symbols (s), (l), (g) and (aq) are often added to balanced equations to show solid, liquid, gas or aqueous (dissolved in water).
配平的方程式常添加物态符号 (s) 固体、(l) 液体、(g) 气体和 (aq) 水溶液（溶于水）。
5. Density and States of Matter | 密度与物质状态
Density is a measure of how much mass is packed into a given volume. The formula links mass, volume and density, and is widely used in chemistry to identify substances or explain separation techniques.
密度衡量的是单位体积内所含质量的大小。该公式将质量、体积和密度联系起来，在化学中广泛用于物质鉴定或解释分离技术。
Density (g/cm³) = mass (g) ÷ volume (cm³) or d = m / V
密度（g/cm³）= 质量（g）÷ 体积（cm³） 或 d = m / V
Solids usually have high densities because particles are packed closely together. Liquids are often slightly less dense than their solids, while gases have very low densities due to large spaces between particles.
固体通常密度较高，因为粒子紧密堆积。液体的密度通常略低于其固体，而气体由于粒子间空隙很大，密度非常低。
During melting or boiling, the mass does not change but the volume alters, so density changes. This principle helps explain why ice floats on water (ice is less dense).
在熔化或沸腾过程中，质量不变但体积改变，因此密度发生变化。这一原理可以解释为何冰浮在水面上（冰的密度较小）。
6. Concentration of Solutions | 溶液浓度
ally expressed in grams per cubic decimetre (g/dm³). Note that 1 dm³ = 1000 cm³ = 1 litre.
浓度描述的是溶解在给定体积溶剂中的溶质含量。八年级通常用克每立方分米（g/dm³）表示浓度。注意 1 dm³ = 1000 cm³ = 1 升。
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）
g of sugar in water to make 0.5 dm³ of solution, the concentration is 10 ÷ 0.5 = 20 g/dm³.
若某同学将 10 g 糖溶于水并配成 0.5 dm³ 溶液，则浓度为 10 ÷ 0.5 = 20 g/dm³。
Remember that adding more solute increases concentration, while adding more solvent (diluting) decreases concentration. The mass of solute remains the same during dilution.
记住，增加溶质会提高浓度，而增加溶剂（稀释）会降低浓度。稀释过程中溶质的质量保持不变。
7. The pH Scale and Acid‑Base Indicators | pH标度与酸碱指示剂
The pH scale measures how acidic or alkaline a solution is. It ranges from 0 to 14, with 7 being neutral. Values below 7 indicate an acid, and values above 7 indicate an alkali (soluble base).
pH 标度用来衡量溶液的酸碱性强弱，范围通常为 0 到 14，7 为中性。小于 7 为酸性，大于 7 为碱性（可溶性碱）。
Acidic: pH < 7 Neutral: pH = 7 Alkaline: pH > 7
酸性：pH < 7 中性：pH = 7 碱性：pH > 7
Universal indicator turns a range of colours from red (strong acid) through green (neutral) to purple (strong alkali). Litmus turns red in acid and blue in alkali.
通用指示剂会呈现从红（强酸）、绿（中性）到紫（强碱）的一系列颜色。石蕊在酸中变红，在碱中变蓝。
lisation occurs when an acid and an alkali react to form a salt and water: H⁺ + OH⁻ → H₂O.
酸在水中产生氢离子（H⁺），碱产生氢氧根离子（OH⁻）。酸碱中和时生成盐和水：H⁺ + OH⁻ → H₂O。
8. Factors Affecting the Rate of Reaction | 影响反应速率的因素
The rate of a chemical reaction tells us how quickly reactants are used up or products are made. Several factors can change the rate.
化学反应速率表示反应物消耗或生成物产生的快慢。有几种因素可以改变反应速率。
Increasing the temperature gives particles more kinetic energy, so they move faster and collide more frequently and with greater energy. This increases the rate.
升高温度使粒子获得更多动能，运动更快，碰撞更频繁且能量更大，因此速率加快。
Increasing the concentration of reactants in a solution (or the pressure of gases) means more particles in the same volume, leading to more frequent collisions and a faster rate.
增加溶液中反应物的浓度（或气体的压强）意味着同一体积内有更多粒子，碰撞更加频繁，速率随之增大。
Using smaller pieces of a solid (larger surface area) exposes more particles to react, so collisions happen more often and the rate rises. A catalyst speeds up a reaction without being used up itself.
将固体研成更小的颗粒（增大表面积）将使更多粒子接触反应物，碰撞机会增多，速率提升。催化剂能加快反应，而自身在反应中不被消耗。
9. Diffusion and Particle Theory | 扩散与粒子理论
Diffusion is the movement of particles from an area of high concentration to an area of low concentration. It happens because particles are in constant, random motion.
扩散是粒子从高浓度区域向低浓度区域运动的过程，其根本原因是粒子处于不停的无规则运动中。
The rate of diffusion is faster in gases than in liquids, because gas particles move more quickly and have more space between them.
气体中的扩散速率比液体中更快，因为气体粒子的运动速度更快，且粒子间距离更大。
Lighter gas particles diffuse faster than heavier ones. This follows Graham' . For example, ammonia (NH₃, Mr=17) diffuses faster than hydrogen chloride (HCl, Mr=36.5).
较轻的气体粒子比较重的扩散得更快。这一定性规律符合格雷姆定律：扩散速率与相对分子质量的平方根成反比。例如氨气（NH₃，Mr=17）比氯化氢（HCl，Mr=36.5）扩散更快。
Diffusion provides evidence for the particle model of matter and explains how smells spread or how a coloured solution slowly disperses in water.
扩散是物质粒子模型的证据之一，也能解释气味如何传播，以及有色溶液如何在水中缓慢扩散。
10. Reactivity Series of Metals | 金属活动性顺序
The reactivity series is a list of common metals arranged from most reactive to least reactive. A more reactive metal can displace a less reactive metal from its compound.
金属活动性顺序是将常见金属按活泼性由强到弱排列的顺序。较活泼的金属能将较不活泼的金属从其化合物中置换出来。
| Metal (symbol) | Metal (Chinese) | Reaction with water / acid |
|---|---|---|
| Potassium (K) | 钾 | Reacts violently with cold water |
| Sodium (Na) | 钠 | Reacts very vigorously with cold water |
| Calcium (Ca) | 钙 | Reacts slowly with cold water |
| Magnesium (Mg) | 镁 | Reacts very slowly with water; reacts vigorously with acids |
| Aluminium (Al) | 铝 | Reacts with acids; protected by oxide layer |
| Zinc (Zn) | 锌 | Reacts with acids |
| Iron (Fe) | 铁 | Reacts slowly with acids |
| Copper (Cu) | 铜 | Does not react with water or dilute acids |
