📚 Year 7 OCR Chemistry: Quick Reference Handbook for Formulas and Theorems | 7年级OCR化学：公式定理速查手册
Welcome to the Year 7 OCR Chemistry Quick Reference Handbook. This concise guide brings together the essential formulas, laws and definitions you will rely on throughout your course. Use it to reinforce what you learn in class and to build confidence before assessments.
欢迎使用7年级OCR化学公式定理速查手册。这本简明指南汇集了课程中你需要依赖的基本公式、定律和定义，帮助你巩固课堂所学，并在评估前建立信心。
1. States of Matter and Changes | 物质状态及其变化
The three fundamental states of matter are solid, liquid and gas. In solids, particles are tightly packed in fixed positions, vibrating in place. In liquids, particles are close together but can slide past each other, allowing the substance to flow. In gases, particles are far apart and move rapidly in all directions at high speeds.
物质有三种基本状态：固态、液态和气态。固体中粒子紧密堆积在固定的位置，原地振动；液体中粒子相距很近但可以相互滑动，使物质能够流动；气体中粒子相距很远，以高速向各个方向运动。
Changes of state involve energy transfer without altering the chemical identity of a substance. The main changes are melting (solid to liquid), freezing (liquid to solid), boiling/evaporation (liquid to gas), condensation (gas to liquid), sublimation (solid to gas) and deposition (gas to solid).
状态变化涉及能量转移而不改变物质的化学性质。主要的变化有熔化（固态变为液态）、凝固（液态变为固态）、沸腾/蒸发（液态变为气态）、冷凝（气态变为液态）、升华（固态直接变为气态）和凝华（气态直接变为固态）。
Solid ⇌ Liquid (melting / freezing) ; Liquid ⇌ Gas (boiling / condensing)
固体 ⇌ 液体（熔化/凝固）；液体 ⇌ 气体（沸腾/冷凝）
The temperature at which a substance melts is its melting point, and the temperature at which it boils is its boiling point. Pure substances have sharp melting and boiling points.
物质熔化时的温度是熔点，沸腾时的温度是沸点。纯物质具有敏锐的熔点和沸点。
2. Atomic Structure Essentials | 原子结构要点
All matter is made of atoms. An atom consists of a central nucleus containing protons and neutrons, surrounded by electrons arranged in shells. Protons carry a positive charge (+1), electrons carry a negative charge (−1) and neutrons have no charge (0).
所有物质都由原子构成。原子由一个包含质子和中子的中心原子核以及按壳层排布的电子组成。质子带正电荷（+1），电子带负电荷（−1），中子不带电（0）。
In a neutral atom, the number of electrons equals the number of protons. The atomic number (Z) is the number of protons, which defines the element. The mass number (A) is the total number of protons plus neutrons.
在中性原子中，电子数等于质子数。原子序数（Z）是质子数，它定义了元素种类。质量数（A）是质子数加中子数的总和。
umber of protons = Z ; Number of electrons (neutral atom) = Z ; Number of neutrons = A − Z
质子数 = Z；电子数（中性原子）= Z；中子数 = A − Z
Elements can be represented with the mass number written at the top left and the atomic number at the bottom left, e.g. ²³₁₁Na for sodium-23. Electrons fill shells in the order 2, 8, 8, ... for the first 20 elements.
元素可以表示为左上角写质量数、左下角写原子序数，例如 ²³₁₁Na 代表钠-23。对于前20号元素，电子按2、8、8……的顺序填充壳层。
3. 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 made of two or more different types of atom chemically bonded together in fixed proportions. A mixture consists of two or more substances (elements or compounds) that are not chemically bonded and can be separated by physical means.
元素是由仅一种原子组成的纯净物。化合物是由两种或多种不同原子以固定比例通过化学键结合而成的纯净物。混合物是由两种或多种物质（元素或化合物）混合而成，它们之间没有化学键结合，可以通过物理方法分离。
Chemical symbols represent elements; for example, H for hydrogen, O for oxygen, Fe for iron. Chemical formulas show the types and numbers of atoms in a compound, such as H₂O (water) containing two hydrogen atoms and one oxygen atom.
化学符号代表元素，例如H代表氢，O代表氧，Fe代表铁。化学式表示化合物中原子的种类和数目，如H₂O（水）含有两个氢原子和一个氧原子。
The periodic table arranges elements by increasing atomic number. Metals are on the left, non-metals on the right, with transitional metals in the central block. Group number often indicates the number of electrons in the outer shell.
元素周期表按原子序数递增排列。金属位于左侧，非金属位于右侧，过渡金属在中央区域。族序数常表明最外层电子数。
4. Chemical Formulas and Equations | 化学式与化学方程式
A chemical equation uses symbols and formulas to describe a reaction. Reactants are written on the left, products on the right, with an arrow between them. The equation must be balanced to show the same number of each type of atom on both sides, obeying the law of conservation of mass.
化学方程式用符号和化学式描述反应。反应物写在左侧，生成物写在右侧，中间用箭头连接。方程式必须配平，使得两边每种原子的数目相等，遵循质量守恒定律。
Word equation: hydrogen + oxygen → water
Balanced symbol equation: 2H₂ + O₂ → 2H₂O
文字方程式：氢气 + 氧气 → 水
配平的符号方程式：2H₂ + O₂ → 2H₂O
To balance equations, adjust the large numbers in front of formulas (coefficients). Never change the small subscript numbers within a formula, as that would change the substance. State symbols are often added: (s) solid, (l) liquid, (g) gas and (aq) aqueous solution.
配平方程式时调整化学式前的大数字（系数），切勿改变化学式内部的下标，否则会改变物质本身。通常还会添加状态符号：(s) 固体，(l) 液体，(g) 气体，(aq) 水溶液。
5. Law of Conservation of Mass | 质量守恒定律
The law of conservation of mass states that the total mass of the reactants equals the total mass of the products in a chemical reaction. Atoms are neither created nor destroyed; they are only rearranged to form new substances.
质量守恒定律指出，在化学反应中，反应物的总质量等于生成物的总质量。原子既不会凭空产生也不会凭空消失，只是重新排列形成了新的物质。
This principle is why chemical equations must be balanced. If a reaction appears to show a mass change, it is usually because a gas has escaped, reacted with air, or been measured in an open system.
这一原理就是化学方程式必须配平的原因。如果一个反应看起来质量发生了改变，通常是因为气体逸出、与空气反应，或在敞口体系中称量所致。
For example, when magnesium is burned in air, the solid product magnesium oxide has a larger mass than the original magnesium because oxygen atoms from the air have combined with the magnesium atoms.
例如，镁在空气中燃烧得到的固体产物氧化镁，其质量大于原来的镁，因为空气中的氧原子与镁原子结合在了一起。
6. Relative Atomic Mass (Ar) and Formula Mass (Mr) | 相对原子质量与式量
The relative atomic mass (Ar) of an element is the average mass of an atom compared to 1/12 of the mass of a carbon-12 atom. It has no unit. The relative formula mass (Mr) of a compound is the sum of the Ar values of all the atoms in its formula.
元素的相对原子质量（Ar）是一个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，没有单位。化合物的相对式量（Mr）是其化学式中所有原子Ar值的总和。
Mr(compound) = sum of Ar of each atom × number of atoms
Mr(化合物) = 每个原子的 Ar × 该原子个数的总和
ulate the Mr of carbon dioxide, CO₂. Ar(C) = 12, Ar(O) = 16. Mr(CO₂) = 12 + (2 × 16) = 44.
例题：计算二氧化碳CO₂的式量。Ar(C)=12，Ar(O)=16。Mr(CO₂) = 12 + (2 × 16) = 44。
Relative formula mass is used to find the percentage of an element in a compound: % = (mass of element in formula / Mr) × 100.
相对式量可用于求元素在化合物中的质量分数：质量分数% = (该元素在化学式中的总质量 / Mr) × 100。
7. The pH Scale and Neutralisation | pH值标度与中和反应
The pH scale ranges from 0 to 14 and measures the acidity or alkalinity of a solution. Values below 7 are acidic, 7 is neutral, and values above 7 are alkaline. The lower the pH, the stronger the acid; the higher the pH, the stronger the alkali.
pH标度范围为0至14，用于衡量溶液的酸碱性。数值小于7为酸性，等于7为中性，大于7为碱性。pH越低酸性越强，pH越高碱性越强。
base → salt + water. A common example is hydrochloric acid reacting with sodium hydroxide.
在中和反应中，酸与碱反应生成盐和水。通用的文字方程式：酸 + 碱 → 盐 + 水。常见的例子是盐酸与氢氧化钠反应。
HCl + NaOH → NaCl + H₂O
盐酸 + 氢氧化钠 → 氯化钠 + 水
er: H⁺ + OH⁻ → H₂O. Universal indicator, litmus and pH probes can be used to determine pH.
酸碱中和涉及的离子是酸中的H⁺(aq)和碱中的OH⁻(aq)，它们结合生成水：H⁺ + OH⁻ → H₂O。通用指示剂、石蕊和pH计可用于测定pH值。
8. Reactivity Series Basics | 反应活性顺序基础
The reactivity series lists metals in order of their reactivity, from most reactive to least reactive. A simple version often used in Year 7 includes: Potassium (K), Sodium (Na), Calcium (Ca), Magnesium (Mg), Aluminium (Al), Carbon (C), Zinc (Zn), Iron (Fe), Hydrogen (H), Copper (Cu), Silver (Ag), Gold (Au).
反应活性序列是按金属活泼性从强到弱排列的顺序。在7年级常用的简化版本包括：钾(K)、钠(Na)、钙(Ca)、镁(Mg)、铝(Al)、碳(C)、锌(Zn)、铁(Fe)、氢(H)、铜(Cu)、银(Ag)、金(Au)。
A more reactive metal can displace a less reactive metal from its compound. For example, magnesium displaces copper from copper sulfate solution because magnesium is above copper in the series.
活泼性较强的金属可以把活泼性较弱的金属从其化合物中置换出来。例如，镁可以把铜从硫酸铜溶液中置换出来，因为镁在活性序列中排在铜之上。
Mg(s) + CuSO₄(aq) → MgSO₄(aq) + Cu(s)
镁 + 硫酸铜溶液 → 硫酸镁溶液 + 铜
Hydrogen is used as a reference: metals above hydrogen react with acids to produce hydrogen gas, while metals below hydrogen generally do not react with dilute acids.
氢被用作参照：位于氢之上的金属可以与酸反应产生氢气，位于氢之下的金属一般不与稀酸反应。
9. Oxidation and Combustion | 氧化与燃烧反应
→ magnesium oxide. In terms of oxygen, the metal is oxidised and oxygen itself is reduced.
氧化最初指物质得到氧的反应。常见的氧化反应是镁在空气中燃烧：镁 + 氧气 → 氧化镁。从氧的角度看，金属被氧化，氧气本身被还原。
2Mg(s) + O₂(g) → 2MgO(s)
2Mg(固) + O₂(气) → 2MgO(固)
Combustion is a rapid reaction with oxygen that releases energy as heat and light. Complete combustion of hydrocarbons produces carbon dioxide and water. For example, methane burns according to the following balanced equation.
燃烧是一种与氧气发生的快速反应，以热和光的形式释放能量。碳氢化合物完全燃烧生成二氧化碳和水。例如，甲烷燃烧遵循以下配平的方程式。
CH₄ + 2O₂ → CO₂ + 2H₂O
甲烷 + 氧气 → 二氧化碳 + 水
Incomplete combustion occurs when oxygen supply is limited, producing carbon monoxide (CO) or carbon (soot) alongside water. Carbon monoxide is a toxic gas.
当氧气供应不足时，会发生不完全燃烧，生成一氧化碳（CO）或碳（烟灰）以及水。一氧化碳是有毒气体。
10. Separation Techniques Overview | 分离技术概述
Different mixtures can be separated using physical methods based on differences in physical properties. Filtration separates an insoluble solid from a liquid using filter paper that traps the solid while the liquid passes through as filtrate.
不同的混合物可以根据物理性质的差异用物理方法分离。过滤利用滤纸把不溶性固体与液体分离，固体被截留而液体作为滤液通过。
Evaporation heats a solution to remove the solvent, leaving the dissolved solid behind. Crystallisation gently heats a solution to form crystals of the dissolved solid as the solvent evaporates slowly.
蒸发通过加热溶液除去溶剂，留下溶解的固体。结晶则通过缓慢蒸发溶剂，使溶解的固体形成晶体。
Simple distillation separates a liquid from a solution by boiling the liquid and then condensing the vapour back into a liquid in a condenser. It works because the solvent has a much lower boiling point than the dissolved solid.
简单蒸馏通过将液体煮沸，再让蒸气在冷凝管中冷凝回液体，从而从溶液中分离出液体。其依据是溶剂的沸点远低于溶解的固体。
Chromatography separates dissolved substances based on how they spread between two phases – a stationary phase (e.g. paper) and a mobile phase (e.g. water). Different substances travel different distances, producing a chromatogram.
色谱法根据溶解的物质在固定相（如纸）和流动相（如水）之间分配行为的差异将其分离。不同物质移动的距离不同，从而得到色谱图。
11. Concentration of Solutions | 溶液浓度
The concentration of a solution tells us how much solute is dissolved in a given volume of solvent. It is commonly expressed in grams per cubic decimetre (g/dm³). One cubic decimetre (1 dm³) is equal to 1000 cm³ or 1 litre.
溶液的浓度表示在一定体积溶剂中溶解了多少溶质，通常以克每立方分米（g/dm³）表示。1立方分米（1 dm³）等于1000 cm³，即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)
concentrated solution contains more solute per unit volume and appears darker in colour if coloured.
例题：若将20g氯化钠溶于0.5 dm³水中，浓度 = 20 / 0.5 = 40 g/dm³。浓度更高的溶液单位体积含更多溶质，若有颜色则显得更深。
: initial concentration × initial volume = final concentration × final volume (when volumes are in the same units).
通过加入更多溶剂将溶液稀释时，浓度会降低，但溶质的总质量保持不变。其关系为：初始浓度 × 初始体积 = 最终浓度 × 最终体积（体积单位需一致）。
12. Common Hazard Symbols | 常见危险标志
Recognising hazard symbols is vital for safety in the laboratory. The 'Corrosive' symbol (depicted by a hand and surface being eaten away) warns of substances that can attack and destroy living tissue, such as strong acids and alkalis.
识别危险标志对实验室安全至关重要。'腐蚀性'标志（显示手和表面被侵蚀）警示那些能攻击和破坏活体组织的物质，如强酸和强碱。
The 'Flammable' symbol (a flame) indicates substances that can catch fire easily, for example ethanol and petrol. 'Oxidising' (a circle with flames above it) alerts that the substance can provide oxygen and make other materials burn more fiercely.
‘易燃’标志（火焰图案）表示物质容易着火，如乙醇和汽油。‘氧化性’标志（圆圈上方有火焰）提醒该物质能提供氧气，使其它材料燃烧得更剧烈。
The 'Explosive' symbol (an exploding bomb) and 'Toxic' (skull and crossbones) warn of substances that can explode or cause serious health damage. 'Harmful/Irritant' (exclamation mark) indicates less severe risks such as skin or eye irritation.
‘爆炸性’标志（爆炸的炸弹）和‘有毒’标志（骷髅交叉骨）警示可能爆炸或导致严重健康损害的物质。‘有害/刺激性’标志（感叹号）表示皮肤或眼睛刺激等较轻的风险。
The 'Environmental hazard' symbol (dead tree and fish) marks substances that can cause lasting damage to aquatic life. Always handle chemicals with care, wear eye protection, and follow your teacher's instructions.
‘环境危害’标志（枯树和死鱼）标示对水生生物可造成长期损害的物质。始终小心处理化学品，佩戴护目镜，并遵循老师的指导。
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