📚 Year 7 CIE Chemistry Formula & Theorem Quick Reference Handbook | 7年级CIE化学公式定理速查手册
Welcome to your handy quick reference guide for Year 7 CIE Chemistry. This handbook summarises the essential formulas, theorems, and key principles you need to master at this stage. Keep it close for revision and problem-solving!
欢迎使用7年级CIE化学公式定理速查手册。本手册汇总了你在这个阶段必须掌握的核心公式、定理与关键原理，方便随时复习和解题。
1. Particle Theory and States of Matter | 粒子理论与物质状态
All matter is made of tiny particles that are in constant motion. The energy, arrangement, and distance between particles determine the physical state.
所有物质都由不断运动的微小粒子构成。粒子能量、排列方式和间距决定了物质的物理状态。
In solids, particles are tightly packed in a regular pattern and vibrate in fixed positions.
在固态中，粒子紧密排列成规则结构，只能在固定位置振动。
In liquids, particles are still close together but can slide past one another, so liquids can flow and take the shape of the container.
在液态中，粒子仍彼此靠近，但能相互滑动，因此液体可以流动并呈现容器的形状。
In gases, particles are far apart, move randomly at high speeds, and completely fill any container.
在气态中，粒子相距很远，以高速随机运动，完全充满容器。
2. Changes of State and Energy | 状态变化与能量
Melting, freezing, boiling, and condensation are physical changes. During a change of state, the temperature remains constant even though heat is being added or removed.
熔化、凝固、沸腾和冷凝属于物理变化。状态变化过程中，即使热量在增加或减少，温度也保持恒定。
The energy supplied during melting or boiling is used to overcome the attractive forces between particles, not to raise the temperature.
熔化或沸腾时提供的能量用于克服粒子间的吸引力，而不会使温度升高。
The reverse processes (freezing, condensation) release energy as particles become more ordered.
相反的相变过程（凝固、冷凝）则因粒子变得更为有序而释放能量。
Melting point = Freezing point ; Boiling point = Condensation point
熔点 = 凝固点 ; 沸点 = 冷凝点
3. Atomic Structure | 原子结构
An atom contains a central nucleus made of protons (positive charge) and neutrons (no charge), with negatively charged electrons arranged in shells around the nucleus.
原子包含由质子（带正电）和中子（不带电）构成的原子核，以及带负电、分层排布在核外的电子。
number (Z) = number of protons. Mass number (A) = number of protons + number of neutrons.
原子序数（Z）= 质子数。质量数（A）= 质子数 + 中子数。
In a neutral atom, the number of electrons equals the number of protons.
在中性原子中，电子数等于质子数。
Number of neutrons = A − Z
中子数 = A − Z
Electrons fill shells according to the 2,8,8 rule for the first 20 elements: the first shell holds up to 2 electrons, the second up to 8, and the third up to 8.
电子排布遵循前20号元素的2,8,8规则：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。
4. Elements, Compounds and Mixtures | 元素、化合物与混合物
An element is a pure substance made of only one type of atom. A compound is a pure substance formed when two or more different elements are chemically bonded in a fixed ratio.
元素是仅由一种原子组成的纯净物。化合物是由两种或以上不同元素以固定比例通过化学键结合而成的纯净物。
A mixture consists of two or more substances (elements or compounds) that are not chemically joined and can be separated by physical methods.
混合物包含两种或以上不通过化学键结合的物质（元素或化合物），可以用物理方法分离。
Compounds obey the law of constant composition: a particular compound always contains the same elements in the same proportions by mass.
化合物遵循定组成定律：一种特定的化合物始终含有相同种类、相同质量比的元素。
5. Chemical Formulae and Valency | 化学式与化合价
A chemical formula uses element symbols and subscript numbers to show the type and number of atoms in a substance. Valency is the combining capacity of an atom.
化学式用元素符号和下标数字表示物质中原子的种类和数目。化合价是原子的结合能力。
To write a formula for an ionic compound, swap the valencies of the combining ions and write them as subscripts. If the valencies are the same, they cancel out.
书写离子化合物的化学式时，交换离子的化合价并将其写为下标；若化合价相同则相互抵消。
l⁻) → NaCl; Calcium oxide (Ca²⁺ and O²⁻) → CaO; Magnesium chloride (Mg²⁺ and Cl⁻) → MgCl₂.
示例：氯化钠（Na⁺ 和 Cl⁻）→ NaCl；氧化钙（Ca²⁺ 和 O²⁻）→ CaO；氯化镁（Mg²⁺ 和 Cl⁻）→ MgCl₂。
6. Relative Atomic Mass (Aᵣ) and Relative Formula Mass (Mᵣ) | 相对原子质量与式量
Aᵣ is the average mass of an atom of an element on a scale where a carbon-12 atom has a mass of exactly 12. Mᵣ is the sum of the relative atomic masses of all atoms in a formula unit.
Aᵣ 是以碳-12原子质量恰好为12为标度时，元素原子的平均质量。Mᵣ 是化学式单元中所有原子的相对原子质量之和。
Mᵣ = Σ (Aᵣ × number of atoms of that element)
Mᵣ = Σ（各元素的 Aᵣ × 该元素原子个数）
Example: Mᵣ(H₂O) = (2 × 1) + 16 = 18. Mᵣ(CO₂) = 12 + (2 × 16) = 44.
示例：Mᵣ(H₂O) = (2 × 1) + 16 = 18；Mᵣ(CO₂) = 12 + (2 × 16) = 44。
7. Percentage Composition by Mass | 元素质量分数
The percentage by mass of an element in a compound can be calculated from the formula of the compound.
可根据化合物的化学式计算某元素在化合物中所占的质量分数。
％ by mass = (number of atoms × Aᵣ of the element / Mᵣ of compound) × 100％
质量分数％ =（原子个数 × 该元素的 Aᵣ / 化合物的 Mᵣ）× 100％
Example: In H₂O, ％ hydrogen = (2 × 1 / 18) × 100％ ≈ 11.1％; ％ oxygen = (16 / 18) × 100％ ≈ 88.9％.
示例：在 H₂O 中，氢的质量分数 = (2 × 1 / 18) × 100％ ≈ 11.1％；氧的质量分数 = (16 / 18) × 100％ ≈ 88.9％。
8. Law of Conservation of Mass | 质量守恒定律
During a chemical reaction, matter is neither created nor destroyed. The total mass of the reactants equals the total mass of the products.
化学反应过程中，物质既不被创造也不被消灭。反应物的总质量等于生成物的总质量。
This means atoms are simply rearranged; the number of each type of atom stays the same before and after the reaction.
这意味着原子只是重新排列；反应前后各类原子的数目保持不变。
If the mass appears to change in an open container, it is usually because a gas has entered or escaped.
如果在敞口容器中质量看似发生了变化，通常是有气体进入或逸出。
9. 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. Follow these steps:
配平的化学方程式中箭头两边各类原子的数目相同。请遵循以下步骤：
Step 1: Write the correct formulae for all reactants and products.
第1步：写出所有反应物和生成物的正确化学式。
Step 2: Count the number of atoms of each element on both sides.
第2步：数一数两边每种元素的原子个数。
Step 3: Add big numbers (coefficients) in front of formulae to balance the atoms — never change the small subscript numbers.
第3步：在化学式前添加大数字（系数）以配平原子——绝不要改动小下标数字。
Example: H₂ + O₂ → H₂O becomes 2H₂ + O₂ → 2H₂O.
示例：H₂ + O₂ → H₂O 配平为 2H₂ + O₂ → 2H₂O。
Check: 4 H atoms and 2 O atoms on each side.
检查：每边各有4个氢原子和2个氧原子。
10. Acids, Bases and the pH Scale | 酸、碱及pH
An acid is a substance that produces hydrogen ions (H⁺) in water. A base is a substance that produces hydroxide ions (OH⁻) in water. Alkalis are soluble bases.
酸是在水中产生氢离子（H⁺）的物质。碱是在水中产生氢氧根离子（OH⁻）的物质。可溶的碱称为碱（alkali）。
The pH scale ranges from 0 to 14: pH < 7 is acidic, pH = 7 is neutral, pH > 7 is alkaline.
pH标度范围为0至14：pH < 7 呈酸性，pH = 7 呈中性，pH > 7 呈碱性。
Universal indicator turns red in strong acids, green in neutral solutions, and purple in strong alkalis.
通用指示剂在强酸中变红，在中性溶液中变绿，在强碱中变紫。
Neutralisation reaction: Acid + Base → Salt + Water. Example: HCl + NaOH → NaCl + H₂O.
中和反应：酸 + 碱 → 盐 + 水。示例：HCl + NaOH → NaCl + H₂O。
11. Rates of Reaction | 反应速率
The rate of a chemical reaction tells us how fast a reactant is used up or a product is formed. It can be increased by raising temperature, increasing concentration, increasing surface area, or adding a catalyst.
化学反应速率表明反应物消耗或产物生成有多快。升高温度、增大浓度、增大表面积或加入催化剂都可以提高反应速率。
Average rate of reaction can be calculated from the change in amount of a product (or reactant) over a period of time.
平均反应速率可以根据一段时间内产物（或反应物）量的变化来计算。
Average rate = change in mass or volume / time taken
平均速率 = 质量或体积的变化值 / 所用时间
Units can be g/s, cm³/s, or g/min depending on the measurement.
单位取决于测量方式，可以是 g/s、cm³/s 或 g/min 等。
12. Mass Concentration | 质量浓度
Mass concentration describes the mass of solute dissolved in a certain volume of solution. It is often used before the mole concept is introduced.
质量浓度描述溶解在一定体积溶液中的溶质质量，常在引入摩尔概念之前使用。
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)
Remember: 1 dm³ = 1000 cm³. So 100 cm³ = 0.1 dm³.
记住：1 dm³ = 1000 cm³。因此 100 cm³ = 0.1 dm³。
f 5 g of salt is dissolved in 250 cm³ of water, concentration = 5 g / 0.25 dm³ = 20 g/dm³.
示例：若将5 g盐溶解在250 cm³水中，浓度 = 5 g / 0.25 dm³ = 20 g/dm³。
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