📚 Cambridge Lower Secondary Complete Chemistry SB 2nd: Core Revision Guide | CIE 剑桥初中化学第二版核心复习指南
This revision guide summarises the key ideas in the Cambridge Lower Secondary Complete Chemistry Student Book (Second Edition). It is designed to help Checkpoint learners review particle theory, elements and compounds, chemical reactions, acids, metals and practical skills. Use the notes alongside past questions and laboratory activities to build confidence before the test.
本复习指南总结了《剑桥初中化学学生用书（第二版）》的核心概念，旨在帮助 Checkpoint 学习者复习粒子理论、元素与化合物、化学反应、酸、金属和实验技能。建议结合历年真题和实验活动一起使用，以便在考试前建立信心。
1. The Particle Model of Matter | 物质的粒子模型
All matter is made of tiny particles that are constantly moving. In solids, particles are closely packed and vibrate in fixed positions. In liquids, particles are close together but can slide past each other. In gases, particles are far apart and move quickly in all directions.
所有物质都由不断运动的微小粒子组成。固体中粒子紧密排列并在固定位置振动；液体中粒子彼此靠近但能相互滑动；气体中粒子相隔很远，并在各个方向上快速运动。
The particle model explains properties such as density, compression and expansion. Gases can be compressed because there is a large space between particles. Solids cannot be compressed easily because the particles are already touching.
粒子模型可以解释密度、压缩和膨胀等性质。气体可以被压缩，是因为粒子之间有较大的空隙；固体难以压缩，是因为粒子已经紧挨在一起。
Heating gives particles more kinetic energy, so they move faster and take up slightly more space. This explains why most substances expand when heated and contract when cooled.
加热使粒子获得更多动能，因此粒子运动更快并占据稍多空间。这解释了为什么大多数物质受热膨胀、冷却收缩。
2. States of Matter and Changes of State | 物质状态与状态变化
Substances can exist as solids, liquids or gases. The state of a substance depends on temperature and pressure, not on the material itself. Water, for example, can be ice, liquid water or steam.
物质可以以固态、液态或气态存在。物质的状态取决于温度和压强，而不是物质本身。例如，水可以是冰、液态水或水蒸气。
Melting, freezing, boiling, condensing, sublimation and deposition are physical changes because no new substance is formed. The particles themselves do not change; only their arrangement and movement change.
熔化、凝固、沸腾、冷凝、升华和凝华都是物理变化，因为没有生成新物质。粒子本身没有改变，改变的只是粒子的排列方式和运动状态。
During a change of state, the temperature stays constant until the change is complete. The energy supplied is used to overcome the forces between particles, not to raise the temperature.
在状态变化过程中，温度保持不变，直到变化完成。所提供的能量用于克服粒子间的作用力，而不是使温度升高。
Diffusion is faster in gases than in liquids because gas particles move faster and have more space between them. A smell spreads quickly across a room because gas particles diffuse rapidly.
气体中的扩散比液体中快，因为气体粒子运动更快且粒子间空间更大。气味能迅速在房间内散开，就是因为气体粒子扩散得很快。
3. Elements, Compounds and Mixtures | 元素、化合物与混合物
An element contains only one type of atom and cannot be broken down into simpler substances by chemical means. Examples of elements include oxygen, iron, sulfur and carbon.
元素只含一种原子，不能用化学方法分解为更简单的物质。元素的例子包括氧、铁、硫和碳。
A compound contains two or more elements chemically joined in fixed proportions. Water (H₂O) always has two hydrogen atoms for every oxygen atom. The properties of a compound are different from the elements that form it.
化合物由两种或两种以上元素以固定比例化合而成。水（H₂O）中每 1 个氧原子总是对应 2 个氢原子。化合物的性质与组成它的元素不同。
A mixture contains different substances that are not chemically joined. Each substance keeps its own properties, and the mixture can often be separated by physical methods such as filtration or distillation.
混合物含有未化合的不同物质。每种物质保持自己的性质，混合物通常可以用过滤、蒸馏等物理方法进行分离。
For example, iron is a magnetic element, sulfur is a yellow non-metal, and iron sulfide is a compound formed when they are heated together. A mixture of iron filings and sulfur can be separated using a magnet.
例如，铁是有磁性的金属元素，硫是黄色非金属，而硫化亚铁是它们一起加热后生成的化合物。铁屑和硫的混合物可以用磁铁进行分离。
4. Atomic Structure and the Periodic Table | 原子结构与元素周期表
Atoms contain protons, neutrons and electrons. Protons have a positive charge, neutrons have no charge, and electrons have a negative charge. Protons and neutrons are found in the nucleus, while electrons move around the nucleus in shells.
原子包含质子、中子和电子。质子带正电，中子不带电，电子带负电。质子和中子位于原子核内，电子则在核外分层运动。
The atomic number is the number of protons in an atom. It identifies the element. In a neutral atom, the number of electrons is equal to the number of protons, so the charges balance.
原子序数是原子中质子的数目，用来识别元素。在中性原子中，电子数等于质子数，因此正负电荷相互平衡。
Elements are arranged in the periodic table in order of increasing atomic number. Groups are vertical columns, and periods are horizontal rows. Elements in the same group have similar chemical properties because they have the same number of outer-shell electrons.
元素在周期表中按原子序数递增排列。族是纵列，周期是横行。同族元素具有相似的化学性质，因为它们的最外层电子数相同。
For example, Group 1 elements are reactive metals, Group 7 elements are reactive non-metals, and Group 0 elements are noble gases that are very unreactive.
例如，第 1 族元素是活泼金属，第 7 族元素是活泼非金属，第 0 族元素是稀有气体，化学性质非常不活泼。
5. Chemical Reactions and Word Equations | 化学反应与文字方程式
In a chemical reaction, reactants are used up and new products are formed. Signs that a reaction has occurred include a colour change, gas bubbles, a temperature change, or the formation of a precipitate.
在化学反应中，反应物被消耗并生成新产物。发生反应的迹象包括颜色变化、产生气泡、温度变化或生成沉淀。
A word equation shows the reactants and products using their names. The arrow means 'reacts to form'. For example, magnesium burns in oxygen to form magnesium oxide.
文字方程式用名称表示反应物和产物。箭头表示“反应生成”。例如，镁在氧气中燃烧生成氧化镁。
magnesium + oxygen → magnesium oxide
镁 + 氧气 → 氧化镁
Conservation of mass states that the total mass of reactants equals the total mass of products. Atoms are rearranged during a reaction, but they are not created or destroyed.
质量守恒定律指出，反应物的总质量等于生成物的总质量。反应过程中原子只是重新排列，没有凭空产生或消失。
6. Acids, Alkalis and Neutralisation | 酸、碱与中和反应
Acids have a pH below 7, alkalis have a pH above 7, and neutral solutions have a pH of 7. Universal indicator changes colour across the pH scale from red in strong acids to purple in strong alkalis.
酸的 pH 值小于 7，碱的 pH 值大于 7，中性溶液的 pH 值为 7。通用指示剂在 pH 区间内呈现不同颜色，从强酸中的红色到强碱中的紫色。
Acids release hydrogen ions (H⁺) in water, while alkalis release hydroxide ions (OH⁻). The pH scale is a measure of the concentration of these ions.
酸在水中释放氢离子（H⁺），碱在水中释放氢氧根离子（OH⁻）。pH 标度是对这些离子浓度的量度。
Neutralisation occurs when an acid reacts with an alkali. The products are always a salt and water.
酸与碱发生中和反应，产物总是盐和水。
acid + alkali → salt + water
酸 + 碱 → 盐 + 水
For example, hydrochloric acid reacts with sodium hydroxide to form sodium chloride and water. Litmus indicator turns red in acid and blue in alkali.
例如，盐酸与氢氧化钠反应生成氯化钠和水。石蕊指示剂在酸中变红，在碱中变蓝。
7. Metals and Non-metals | 金属与非金属
Metals are usually shiny, good conductors of heat and electricity, malleable and ductile. Most metals are solid at room temperature, but mercury is a liquid.
金属通常有光泽，是热和电的良导体，具有延展性和可锻性。大多数金属在室温下为固体，但汞是液体。
Non-metals are generally dull and poor conductors of heat and electricity. Many non-metals are gases at room temperature, such as oxygen and nitrogen, while others are brittle solids like sulfur.
非金属通常无光泽，是热和电的不良导体。许多非金属在室温下是气体，如氧气和氮气，另一些则是脆性固体，如硫。
Metal oxides are basic and often react with acids to form salts. Non-metal oxides are usually acidic and can react with alkalis. This difference can be tested using indicators.
金属氧化物呈碱性，常与酸反应生成盐。非金属氧化物通常呈酸性，能与碱反应。这种差异可以用指示剂进行检验。
8. The Reactivity Series and Displacement | 活动性顺序与置换反应
The reactivity series lists metals in order of how readily they react. Potassium and sodium are very reactive, while gold and silver are very unreactive. Carbon and hydrogen are often included in the series for comparison.
活动性顺序按照金属反应的难易程度排列。钾和钠非常活泼，而金和银非常不活泼。为了比较，碳和氢也常被列入活动性顺序。
A more reactive metal can displace a less reactive metal from its compound. For example, iron is more reactive than copper, so iron can displace copper from copper sulfate solution.
较活泼的金属能从化合物中置换出较不活泼的金属。例如，铁比铜活泼，因此铁能从硫酸铜溶液中置换出铜。
iron + copper sulfate → iron sulfate + copper
铁 + 硫酸铜 → 硫酸亚铁 + 铜
During displacement, the more reactive metal loses electrons and forms positive ions. The less reactive metal ions gain electrons and become neutral atoms. This is why the less reactive metal appears as a solid deposit.
在置换反应中，较活泼金属失去电子形成阳离子。较不活泼金属离子得到电子变成中性原子。这就是较不活泼金属以固体沉积物形式出现的原因。
9. Separation Techniques for Mixtures | 混合物的分离技术
Filtration separates an insoluble solid from
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