📚 Year 8 Cambridge Chemistry: Formulas & Theorems Quick Reference | 剑桥八年级化学公式定理速查手册
This quick reference handbook covers the essential formulas, key theorems, and fundamental principles you need to master in Year 8 Cambridge Chemistry. Keep it handy for revision and rapid recall.
本速查手册涵盖了剑桥八年级化学中必须掌握的核心公式、关键定理和基本原理。随身携带，方便复习与快速回忆。
1. Particle Theory and States of Matter | 粒子理论与物质状态
All matter is made of tiny particles. The arrangement and movement of these particles determine the state of matter.
所有物质都由微小粒子构成。粒子的排列方式和运动状态决定了物质的三态。
In solids, particles are closely packed in a regular pattern and vibrate in fixed positions. In liquids, particles are close together but can move past each other. In gases, particles are far apart and move rapidly in all directions.
固体中，粒子紧密排列成规则结构，只能在固定位置振动。液体中，粒子仍紧密但可相互滑动。气体中，粒子间距很大，向各个方向快速运动。
The energy of particles increases from solid to liquid to gas. Changes of state (melting, boiling, condensation, freezing) occur at specific temperatures without a change in particle identity.
粒子能量从固体到液体再到气体依次增大。物态变化（熔化、沸腾、凝结、凝固）发生在特定温度，粒子本身不改变。
2. Atomic Structure: Protons, Neutrons, Electrons | 原子结构：质子、中子、电子
Atoms consist of a nucleus containing protons and neutrons, surrounded by electrons in shells. The atomic number (Z) is the number of protons; the mass number (A) is the total number of protons and neutrons.
原子由包含质子和中子的原子核以及核外分层排布的电子构成。原子序数 (Z) 等于质子数；质量数 (A) 等于质子数与中子数之和。
s = Z Number of electrons = Z (in a neutral atom) Number of neutrons = A − Z
In a neutral atom, the number of electrons equals the number of protons. Ions form when electrons are lost or gained.
中性原子中，电子数等于质子数。原子得到或失去电子后形成离子。
3. Electron Arrangement Rules | 电子排布规则
Electrons occupy shells around the nucleus. The first shell holds up to 2 electrons, the second up to 8, and the third up to 8 (for the first 20 elements).
电子占据原子核外的电子层。第一层最多容纳 2 个电子，第二层最多 8 个，第三层最多 8 个（适用于前 20 号元素）。
. Chlorine (Cl, Z=17) → 2,8,7. The arrangement determines chemical reactivity and valency.
例如：钠 (Na, Z=11) 的电子排布为 2,8,1。氯 (Cl, Z=17) 为 2,8,7。电子排布决定了元素的化学反应活性和化合价。
4. Writing Chemical Formulae with Valency | 化学式书写与化合价
The chemical formula of a compound shows the ratio of atoms. Use the valency (combining power) of each element or ion and swap the numbers to get the simplest ratio.
化合物的化学式表示原子个数比。利用元素或离子的化合价（结合能力），交叉价数并化简为最简整数比。
Example: Al³⁺ and O²⁻ → Al₂O₃
reat the whole ion as a unit: sulfate SO₄²⁻, nitrate NO₃⁻, carbonate CO₃²⁻, hydroxide OH⁻.
常见化合价：第 I 族为 1，第 II 族为 2，第 III 族为 3，氧为 2，氯为 1。对于多原子离子，将整个离子团作为一个整体处理：硫酸根 SO₄²⁻、硝酸根 NO₃⁻、碳酸根 CO₃²⁻、氢氧根 OH⁻。
For ionic compounds, the total positive charge must balance the total negative charge.
离子化合物中，正负电荷总数必须相互抵消。
5. Relative Atomic Mass (Aᵣ) | 相对原子质量
The relative atomic mass (Aᵣ) of an element is the average mass of its atoms compared to 1/12 of the mass of a carbon‑12 atom. It has no units.
元素的相对原子质量 (Aᵣ) 是其原子的平均质量与一个碳‑12 原子质量的 1/12 相比较的比值，无单位。
e the integer or one-decimal-place value: e.g., H = 1, C = 12, O = 16, Na = 23, Cl = 35.5.
Aᵣ 值可从元素周期表中获取。计算时常取整数或一位小数：例如 H = 1、C = 12、O = 16、Na = 23、Cl = 35.5。
Aᵣ is used to work out how many atoms of different elements are present in a given sample and in formula mass calculations.
Aᵣ 用于计算给定样品中不同元素的原子数目以及化学式量。
6. Relative Molecular Mass (Mᵣ) | 相对分子质量
The relative molecular mass (Mᵣ) is the sum of the relative atomic masses of all the atoms in a chemical formula. It is used for both molecular compounds and giant covalent structures, and it has no units.
相对分子质量 (Mᵣ) 是一个化学式中所有原子的相对原子质量之和。适用于分子化合物和巨型共价结构，无单位。
Mᵣ = Σ Aᵣ of every atom in the formula
de CO₂ → Mᵣ = 12 + (2 × 16) = 44. Calcium carbonate CaCO₃ → Mᵣ = 40 + 12 + (3 × 16) = 100.
例如：水 H₂O → Mᵣ = (2 × 1) + (1 × 16) = 18。二氧化碳 CO₂ → Mᵣ = 12 + (2 × 16) = 44。碳酸钙 CaCO₃ → Mᵣ = 40 + 12 + (3 × 16) = 100。
Mᵣ is essential for understanding reacting masses and conservation of mass in equations.
Mᵣ 对于理解反应质量以及方程式中的质量守恒至关重要。
7. Balancing Chemical Equations | 配平化学方程式
A balanced chemical equation has the same number of each type of atom on both sides of the arrow. This reflects the law of conservation of mass.
配平的化学方程式在箭头两侧各种原子的数目相等。这体现了质量守恒定律。
To balance an equation, place whole number coefficients (the big numbers in front of formulas) until the atom count matches. Never change the small subscript numbers inside a formula.
配平方程时，在化学式前添加整数系数（大数字），直到各种原子数目一致。切勿改变化学式内部的下角标数字。
H₂O (unbalanced). Balanced: 2H₂ + O₂ → 2H₂O. Check: 4 H atoms and 2 O atoms on each side.
例如：H₂ + O₂ → H₂O（未配平）。配平后：2H₂ + O₂ → 2H₂O。检查：每侧各 4 个 H 原子和 2 个 O 原子。
- Start with elements that appear in only one reactant and one product.
- Save oxygen and hydrogen (if present) for last.
- Always give the final equation in the simplest whole-number ratio.
- 先从只出现在一种反应物和一种生成物中的元素开始。
- 将氧和氢（如果存在）留到最后配平。
- 最终方程式中的系数应为最简整数比。
8. Law of Conservation of Mass | 质量守恒定律
During a chemical reaction, no atoms are created or destroyed. Therefore, the total mass of reactants equals the total mass of products.
化学反应过程中，没有原子被创造或毁灭。因此，反应物的总质量等于生成物的总质量。
This means you can predict the mass of a product or reactant if all other masses are known, using the balanced equation and Mᵣ.
这意味着如果已知其他物质的质量，可以利用配平的化学方程式和 Mᵣ 来预测某种生成物或反应物的质量。
In an open system, mass may appear to change if a gas enters or escapes, but the total mass of the closed system remains constant.
在开放系统中，如果有气体进入或逸出，质量可能看似改变，但在封闭系统中总质量保持不变。
Total mass of reactants = Total mass of products
9. The pH Scale and Acids & Bases | pH 标度与酸碱
The pH scale measures how acidic or alkaline a solution is. It ranges from 0 to 14.
pH 标度用于衡量溶液的酸碱程度，范围从 0 到 14。
| pH < 7 | Acidic – contains excess H⁺(aq) ions |
| pH = 7 | Neutral – equal H⁺ and OH⁻, e.g. pure water |
| pH > 7 | Alkaline – contains excess OH⁻(aq) ions |
or gives a range of colours: red (strong acid) → green (neutral) → violet (strong alkali).
指示剂如石蕊、通用指示剂或酚酞会根据 pH 改变颜色。通用指示剂呈现一系列颜色：红色（强酸）→ 绿色（中性）→ 紫色（强碱）。
10. General Equation for Neutralisation | 中和反应通式
Neutralisation is the reaction between an acid and a base (or alkali) to produce a salt and water. The essential ionic process is:
中和反应是酸与碱（或可溶性碱）反应生成盐和水的过程。其本质离子反应为：
H⁺(aq) + OH⁻(aq) → H₂O(l)
In terms of compounds:
以化合物形式表示：
Acid + Base → Salt + Water
Sulfuric acid + copper(II) oxide → copper(II) sulfate + water (H₂SO₄ + CuO → CuSO₄ + H₂O).
例如：盐酸 + 氢氧化钠 → 氯化钠 + 水 (HCl + NaOH → NaCl + H₂O)。硫酸 + 氧化铜 → 硫酸铜 + 水 (H₂SO₄ + CuO → CuSO₄ + H₂O)。
e acid used: hydrochloric acid → chloride, sulfuric acid → sulfate, nitric acid → nitrate.
盐的名称由金属（或铵根）和所用的酸决定：盐酸 → 氯化物，硫酸 → 硫酸盐，硝酸 → 硝酸盐。
11. Reaction of Metals with Acids | 金属与酸反应
Many metals react with dilute acids to produce a salt and hydrogen gas. The general equation is:
许多金属与稀酸反应生成盐和氢气。通式为：
Metal + Acid → Salt + Hydrogen
: Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g). The test for hydrogen is a lighted splint giving a 'squeaky pop' sound.
例如：Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g)。检验氢气的方法是用燃着的木条点燃，会发出“噗”的一声爆鸣。
Not all metals react with acids; metals below hydrogen in the reactivity series (e.g., copper, silver, gold) do not produce hydrogen with dilute acids.
并非所有金属都能与酸反应；在金属活动性顺序中排在氢之后的金属（如铜、银、金）与稀酸反应不产生氢气。
12. The Reactivity Series | 反应性序列
The reactivity series lists metals in order of how vigorously they react, mainly with water and acids. A common mnemonic order (most reactive first) is:
反应性序列根据金属与水和酸反应的剧烈程度排列。常见的记忆顺序（由强到弱）为：
Potassium > Sodium > Calcium > Magnesium > Aluminium > Zinc > Iron > Lead > (Hydrogen) > Copper > Silver > Gold
Potassium, sodium and lithium react violently with water, producing metal hydroxide and hydrogen gas. Magnesium reacts very slowly with cold water but vigorously with steam. Copper does not react with dilute acids; silver and gold are very unreactive.
钾、钠、锂与水剧烈反应，生成金属氢氧化物和氢气。镁与冷水反应极缓慢，但在高温水蒸气中剧烈反应。铜不与稀酸反应；银和金非常不活泼。
from their compounds. For example, iron + copper(II) sulfate → iron(II) sulfate + copper.
活泼性较强的金属能把活泼性较弱的金属从其化合物中置换出来。例如，铁 + 硫酸铜 → 硫酸亚铁 + 铜。
The reactivity series helps predict whether a displacement reaction will occur and choose suitable metal extraction methods.
反应性序列有助于预测置换反应能否发生，并选择合适的金属提炼方法。
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