Year 8 CAIE Chemistry: Quick Reference Handbook of Formulas and Theorems | Year 8 CAIE 化学：公式定理速查手册

📚 Year 8 CAIE Chemistry: Quick Reference Handbook of Formulas and Theorems | Year 8 CAIE 化学：公式定理速查手册

Mastering the fundamental formulas and theorems in Year 8 Chemistry is the cornerstone for building a solid scientific foundation. This handbook compiles the key equations, definitions, and conceptual relationships required by the CAIE Lower Secondary Science curriculum. Use it as your go-to revision companion to memorise essential facts and apply them confidently in problem-solving scenarios.

掌握八年级化学的基础公式和定理是构建稳固科学基础的基石。这份手册汇编了 CAIE 初中科学课程所要求的关键方程式、定义和概念关系。把它当作你首选的复习伙伴，用来记忆基本事实，并在解题情境中自信地应用它们。

1. States of Matter and Particle Theory | 物质状态与粒子理论

All matter is made up of tiny particles (atoms or molecules) that are in constant, random motion. The energy of these particles and the strength of the forces between them determine whether a substance is a solid, liquid, or gas. During changes of state, the temperature remains constant while the existing bonds are being overcome; this is called the latent heat principle.

所有物质都由不断进行无规则运动的微小粒子（原子或分子）构成。这些粒子的能量以及它们之间作用力的强弱，决定了物质是固态、液态还是气态。在状态变化期间，当原有联结被克服时温度保持恒定；这被称为潜热原理。

Solids: Particles are closely packed in a regular arrangement, vibrating in fixed positions.
固体：粒子紧密排列成规则结构，在固定位置上振动。
Liquids: Particles are close together but can move past each other, taking the shape of the container.
液体：粒子彼此靠近但能相互滑动，呈现容器的形状。
Gases: Particles are far apart, moving rapidly and randomly in all directions.
气体：粒子相距很远，向各个方向快速而无规则地运动。

The kinetic particle theory explains diffusion, where particles of a gas or dissolved substance spread from an area of high concentration to low concentration until evenly distributed. A heavier gas diffuses more slowly than a lighter gas at the same temperature.

运动粒子理论能解释扩散现象，即气体或溶解物质的粒子从高浓度区域向低浓度区域扩散，直到均匀分布。在相同温度下，较重的气体比轻的气体扩散得更慢。

Rate of Diffusion ∝ 1 / √(Molar Mass)

2. Atomic Structure and the Periodic Table | 原子结构与元素周期表

Atoms are the smallest particles of an element that can take part in a chemical reaction. Each atom contains a central nucleus made of protons (positive charge) and neutrons (no charge), surrounded by electrons (negative charge) arranged in shells. The atomic number (Z) equals the number of protons, which defines the element’s identity. The mass number (A) is the total number of protons plus neutrons.

原子是能参与化学反应的元素的最小粒子。每个原子包含一个由质子（带正电）和中子（不带电）构成的中心原子核，核外是分层排布的电子（带负电）。原子序数 (Z) 等于质子数，决定了元素的身份。质量数 (A) 是质子数与中子数的总和。

Mass Number (A) = Number of Protons + Number of Neutrons

An atom is electrically neutral overall, so the number of protons equals the number of electrons. Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons; they have identical chemical properties but different physical properties such as density.

原子整体呈电中性，因此质子数与电子数相等。同位素是质子数相同但中子数不同的同一种元素的原子；它们的化学性质完全相同，但物理性质（如密度）不同。

Particle	Charge	Mass (relative)
Proton	+1	1
Neutron	0	1
Electron	-1	1/1836

3. Electron Configuration and Valency | 电子排布与化合价

Electrons occupy shells around the nucleus. The first shell holds a maximum of 2 electrons, the second shell holds up to 8, and the third shell also holds up to 8 for the first 20 elements. The arrangement of electrons, or electron configuration, determines how an atom bonds with others. Atoms strive to achieve a full outer shell, following the noble gas configuration (usually 8 electrons, or 2 for helium).

电子占据原子核周围的电子层。第一层最多容纳 2 个电子，第二层最多容纳 8 个，而对于前 20 种元素，第三层也最多容纳 8 个。电子的排列方式，即电子排布，决定了原子如何与其他原子键合。原子力求达到满的外层结构，遵循惰性气体排布（通常为 8 个电子，氦为 2 个）。

Valency refers to the combining power of an element. For a metal atom, the valency is usually equal to the number of electrons in its outermost shell, which it will likely lose to form a positive ion (cation). For a non-metal, the valency is typically 8 minus the number of outer-shell electrons, representing how many electrons it will gain to form a negative ion (anion).

化合价指元素的结合能力。对于金属原子，化合价通常等于其最外层电子数，金属倾向于失去这些电子形成正离子（阳离子）。对于非金属，化合价通常是 8 减去其最外层电子数，这代表它将获得多少电子以形成负离子（阴离子）。

Valency of a non-metal = 8 − Number of outer-shell electrons

4. Writing Chemical Formulae | 化学式的书写

Chemical formulae are written by cross-referencing the valencies of the combining elements or ions. The total positive charge must equal the total negative charge in a neutral compound. For ionic compounds, the metal (or positive ion) is always written first, followed by the non-metal or negative radical. Parentheses are used when a radical such as sulfate (SO₄²⁻) or hydroxide (OH⁻) takes more than one unit.

化学式是通过交叉参照结合元素或离子的化合价来书写的。在中性化合物中，正电荷总数必须等于负电荷总数。对于离子化合物，金属（或正离子）总是写在前面，后面是非金属或负离子根。当硫酸根 (SO₄²⁻) 或氢氧根 (OH⁻) 等原子团需要一个以上时，需使用括号。

For example, magnesium chloride: the Mg²⁺ ion has a valency of 2, and the Cl⁻ ion has a valency of 1. By cross-multiplying, we get one Mg²⁺ combining with two Cl⁻, giving the formula MgCl₂. For aluminium sulfate, Al³⁺ has a valency of 3, and SO₄²⁻ has a valency of 2; crossing these gives Al₂(SO₄)₃.

例如，氯化镁：Mg²⁺ 离子的化合价为 2，Cl⁻ 离子的化合价为 1。通过交叉相乘，我们得到一个 Mg²⁺ 结合两个 Cl⁻，化学式为 MgCl₂。对于硫酸铝，Al³⁺ 的化合价为 3，SO₄²⁻ 的化合价为 2；交叉相乘得到 Al₂(SO₄)₃。

5. Balancing Chemical Equations | 化学方程式的配平

A chemical equation describes a chemical change using symbols and formulae. The Law of Conservation of Mass states that atoms are neither created nor destroyed in a chemical reaction, so the number of each type of atom must be the same on both sides of the equation. Balancing an equation ensures that the total mass of reactants equals the total mass of products.

化学方程式用符号和化学式描述化学变化。质量守恒定律指出，在化学反应中，原子既不会被创造也不会被毁灭，因此每种原子的数量在方程式两边必须相等。配平方程可以确保反应物的总质量等于生成物的总质量。

Start by writing the correct formulae for all reactants and products. Then change only the coefficients (the large numbers in front of each formula) to balance the atoms, never alter the subscripts within a formula. Finally, check the atom count for every element. State symbols (s), (l), (g), and (aq) indicate solid, liquid, gas, and aqueous solution respectively.

首先写出所有反应物和生成物的正确化学式。然后只改变系数（每个化学式前的大数字）来配平原子，绝不能更改化学式内部的下标数字。最后，检查每种元素的原子数。状态符号 (s)、(l)、(g) 和 (aq) 分别表示固态、液态、气态和水溶液。

2H₂(g) + O₂(g) → 2H₂O(l)

6. 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) of an element is the average mass of one atom of that element compared to 1/12 of the mass of a carbon-12 atom. It has no units because it is a ratio. For chlorine, with two main isotopes (Cl-35 and Cl-37), a weighted average is used. The relative molecular mass (Mr) is the sum of the Ar values of all the atoms in a molecule or formula unit.

元素的相对原子质量 (Ar) 是指该元素一个原子的平均质量与碳-12 原子质量的 1/12 的比值。它没有单位，因为它是一个比率。对于氯，有两种主要同位素 (Cl-35 和 Cl-37)，需要使用加权平均值。相对分子质量 (Mr) 是分子或化学式单元中所有原子的 Ar 值的总和。

Mr of CO₂ = 12 + (16 × 2) = 44

This concept is important when calculating the percentage composition by mass of an element in a compound. The formula is the total mass of the element in one mole of the compound divided by the Mr of the compound, multiplied by 100%.

在计算化合物中某元素的质量百分比组成时，这个概念很重要。其公式是：一摩尔化合物中该元素的总质量除以该化合物的 Mr，再乘以 100%。

Percentage by mass = (Mass of element in 1 mole / Mr of compound) × 100%

7. The Mole and Molar Mass | 摩尔与摩尔质量

A mole is the SI unit for the amount of substance. One mole of any substance contains exactly 6.02 × 10²³ particles (Avogadro constant, Nₐ). The molar mass (M) of a substance is the mass of one mole of that substance, expressed in grams per mole (g/mol). Numerically, the molar mass is equal to the relative atomic mass (Ar) or relative molecular mass (Mr).

摩尔是物质的量的国际单位 (SI)。一摩尔的任何物质恰好包含 6.02 × 10²³ 个粒子（阿伏伽德罗常数，Nₐ）。物质的摩尔质量 (M) 是该物质一摩尔的质量，以克每摩尔 (g/mol) 表示。在数值上，摩尔质量等于相对原子质量 (Ar) 或相对分子质量 (Mr)。

The relationship between moles, mass, and molar mass is one of the most frequently used quantitative formulas in chemistry. Always ensure the mass is in grams before substituting into the equation. This triangle relationship allows you to find any one variable if the other two are known.

摩尔、质量和摩尔质量之间的关系是化学中定量计算最常用的公式之一。在代入方程之前，务必确保质量以克为单位。这种三角关系可以用已知的任意两个变量来求取第三个变量。

Number of moles (n) = Mass (m) / Molar mass (M)

8. Reacting Mass Calculations | 反应质量计算

Stoichiometry uses the balanced chemical equation to determine the relationships between the amounts of reactants and products. The mole ratio from the coefficients in the balanced equation is used as the conversion bridge. A stepwise approach is crucial: first convert the known mass to moles, then use the mole ratio to find moles of the unknown, and finally convert moles of the unknown back to mass.

化学计量学利用配平后的化学方程式来确定反应物与生成物数量之间的关系。配平方程中的系数所表示的摩尔比被用作转换的桥梁。分步计算法至关重要：首先将已知质量转换为摩尔，接着利用摩尔比求未知物的摩尔数，最后将未知物的摩尔数转换回质量。

For example, to find how much water is produced from 4.0 g of hydrogen gas reacting with excess oxygen: first calculate moles of H₂ = 4.0 g / 2 g/mol = 2.0 mol. From the equation 2H₂ + O₂ → 2H₂O, the mole ratio of H₂ to H₂O is 1:1, so 2.0 mol of H₂O are formed. Mass of H₂O = 2.0 mol × 18 g/mol = 36 g.

例如，要找出 4.0 克氢气与过量氧气反应生成多少水：首先计算 H₂ 的摩尔数 = 4.0g / 2g/mol = 2.0 mol。根据方程式 2H₂ + O₂ → 2H₂O，H₂ 与 H₂O 的摩尔比为 1:1，因此生成 2.0 mol 的 H₂O。H₂O 的质量 = 2.0 mol × 18 g/mol = 36 g。

9. Concentration of Solutions | 溶液的浓度

The concentration of a solution describes how much solute is dissolved in a given volume of solvent. The most common units of concentration in Year 8 are grams per cubic decimetre (g/dm³) or moles per cubic decimetre (mol/dm³). One cubic decimetre (dm³) is equivalent to 1000 cm³ or 1 litre. The formula is straightforward but requires careful attention to volume unit conversions.

溶液浓度描述了给定体积的溶剂中溶解了多少溶质。八年级化学中最常用的浓度单位是克每立方分米 (g/dm³) 或摩尔每立方分米 (mol/dm³)。一立方分米 (dm³) 等于 1000 cm³ 或 1 升。公式虽然简单，但需要仔细注意体积单位的换算。

Concentration (g/dm³) = Mass of solute (g) / Volume of solution (dm³)

A more concentrated solution has a higher ratio of solute to solvent. When a solution is diluted by adding more solvent, the number of moles of solute remains unchanged, but the volume increases, thereby decreasing the concentration. The dilution law is often expressed as C₁V₁ = C₂V₂, where C is concentration and V is volume.

较浓的溶液具有较高的溶质与溶剂之比。当通过添加更多溶剂来稀释溶液时，溶质的摩尔数保持不变，但体积增大，从而降低浓度。稀释定律常表示为 C₁V₁ = C₂V₂，其中 C 是浓度，V 是体积。

10. Acids, Bases and the pH Scale | 酸、碱与 pH 值

Acids are substances that donate hydrogen ions (H⁺) when dissolved in water. Common laboratory acids include hydrochloric acid (HCl), sulfuric acid (H₂SO₄), and nitric acid (HNO₃). Bases are substances that accept hydrogen ions or release hydroxide ions (OH⁻). Alkalis are soluble bases, such as sodium hydroxide (NaOH) and potassium hydroxide (KOH).

酸是溶于水时能释放出氢离子 (H⁺) 的物质。常见的实验室用酸包括盐酸 (HCl)、硫酸 (H₂SO₄) 和硝酸 (HNO₃)。碱是能接受氢离子或释放氢氧根离子 (OH⁻) 的物质。可溶性碱被称为碱溶液，例如氢氧化钠 (NaOH) 和氢氧化钾 (KOH)。

The pH scale measures the acidity or alkalinity of a solution, ranging from 0 (strongly acidic) to 14 (strongly alkaline), with 7 being neutral. The scale is logarithmic, meaning a change of one pH unit represents a tenfold change in H⁺ ion concentration. Universal indicator is a mixture of dyes that shows a range of colours across the pH scale.

pH 值范围是衡量溶液酸碱性强弱的指标，范围从 0（强酸性）到 14（强碱性），其中 7 为中性。该标度是对数标度，意味着 pH 值每改变一个单位，H⁺ 离子浓度就会发生十倍的变化。通用指示剂是一种混合染料，能在不同 pH 值范围内显示一系列颜色。

The reaction between an acid and a base is called neutralisation, which always produces a salt and water. The ionic equation for neutralisation shows that the hydrogen ion from the acid combines with the hydroxide ion from the base to form water.

酸与碱之间的反应称为中和反应，总会生成一种盐和水。中和反应的离子方程式表明，来自酸的氢离子与来自碱的氢氧根离子结合生成水。

H⁺(aq) + OH⁻(aq) → H₂O(l)

11. Rates of Reaction and Collision Theory | 反应速率与碰撞理论

The rate of a chemical reaction is the speed at which reactants are converted into products. It can be measured by monitoring the volume of gas produced over time, the change in mass, or the disappearance of a colour. Collision theory states that for a reaction to occur, particles must collide with sufficient energy and the correct orientation.

化学反应速率是指反应物转化为生成物的速度。它可以通过监测随时间产生的气体体积、质量变化或颜色消失来测量。碰撞理论指出，要发生反应，粒子必须以足够的能量和正确的取向发生碰撞。

The minimum energy required for a reaction to proceed is called the activation energy (Eₐ). Four factors affect the rate: concentration (more particles in the same volume leads to more frequent collisions), surface area (smaller pieces expose more surface for collisions), temperature (particles move faster and have more energy), and the presence of a catalyst (provides an alternative pathway with lower activation energy).

反应进行所需的最低能量称为活化能 (Eₐ)。影响速率的因素有四个：浓度（相同体积内粒子越多，碰撞越频繁）、表面积（颗粒越小，暴露的碰撞面越多）、温度（粒子运动更快且能量更高）以及催化剂的存在（提供一条活化能更低的替代途径）。

12. Separation Techniques | 分离技术

Mixtures can be separated using physical methods that exploit the differences in physical properties of their components. Filtration is used to separate an insoluble solid from a liquid. Crystallisation involves heating a solution to evaporate the solvent, leaving behind crystals of the dissolved solid. Simple distillation separates a pure liquid from a mixture by boiling and condensing the liquid.

混合物可以利用各组分物理性质的差异，通过物理方法进行分离。过滤用于将不溶性固体从液体中分离出来。结晶涉及加热溶液蒸发溶剂，留下溶解固体的晶体。简单蒸馏通过将液体煮沸并冷凝，从混合物中分离出纯液体。

Fractional distillation is used to separate two or more liquids with different boiling points, such as ethanol and water. Chromatography separates soluble substances based on their different solubilities in a solvent, producing a chromatogram. The Rf value (retention factor) is a useful comparative measure: Rf = distance moved by spot / distance moved by solvent front.

分馏用于分离两种或多种沸点不同的液体，例如乙醇和水。色谱法根据不同物质在溶剂中的溶解度差异来分离可溶性物质，生成色谱图。比移值 (Rf) 是一个有用的比较衡量指标：Rf = 斑点移动的距离 / 溶剂前沿移动的距离。

Rf = Distance travelled by substance / Distance travelled by solvent

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Year 8 CAIE Chemistry: Quick Reference Handbook of Formulas and Theorems | Year 8 CAIE 化学：公式定理速查手册