📚 Year 8 Cambridge Chemistry: Core Knowledge Review | Year 8 剑桥化学：核心知识点梳理
Welcome to your complete revision guide for Year 8 Cambridge Chemistry. Whether you are preparing for an end-of-stage test or simply consolidating what you have learned in class, this article covers the most important topics from the Cambridge Lower Secondary Science curriculum. We will explore states of matter, atoms, elements, compounds, chemical reactions, acids and alkalis, and the reactivity of metals — all explained clearly with key definitions and examples.
欢迎阅读 Year 8 剑桥化学综合复习指南。无论你是在准备阶段末考试，还是想巩固课堂所学，本文都涵盖了剑桥初中科学课程中最重要的知识点。我们将梳理物质状态、原子、元素、化合物、化学反应、酸和碱以及金属活动性等核心主题，每个要点都配有清晰的定义和实例。
1. States of Matter and Particle Theory | 物质状态与粒子理论
All matter is made of tiny particles that are constantly moving. The three common states of matter are solid, liquid and gas. In a solid, particles are packed closely in a regular pattern and can only vibrate in fixed positions. In a liquid, particles are still close together but can move past each other, allowing the liquid to flow. In a gas, particles are far apart and move rapidly in all directions.
所有物质都是由不断运动的微小粒子构成的。常见的三种物质状态是固态、液态和气态。固态时，粒子紧密排列成规则结构，只能在固定位置振动。液态时，粒子仍然彼此靠近，但能相互滑动，使液体能够流动。气态时，粒子相距很远，朝各个方向快速运动。
The particle model helps explain changes of state. When a solid is heated, particles gain energy and vibrate faster; at the melting point, the regular structure breaks down and the solid becomes a liquid. Further heating gives particles enough energy to overcome attractive forces completely, changing the liquid into a gas at the boiling point.
粒子模型有助于解释状态变化。固体受热时，粒子获得能量振动加快；到达熔点时，规则结构被破坏，固体变为液体。继续加热使粒子获得足够能量完全克服吸引力，液体在沸点变为气体。
Diffusion is the movement of particles from an area of higher concentration to an area of lower concentration. It occurs in liquids and gases but not in solids because particles in solids cannot move freely. Heavier particles diffuse more slowly than lighter ones, and diffusion speeds up at higher temperatures.
扩散是指粒子从高浓度区域向低浓度区域运动的过程。扩散发生在液体和气体中，但不会发生在固体中，因为固体粒子不能自由移动。较重的粒子扩散速度比较轻的粒子慢，温度升高时扩散加快。
2. Atoms and Elements | 原子与元素
An element is a substance made of only one type of atom. Atoms are the smallest particles of an element that still have the properties of that element. All known elements are listed in the Periodic Table, and each has its own chemical symbol, such as H for hydrogen and O for oxygen.
元素是仅由一种原子组成的物质。原子是元素最小的粒子，仍保持该元素的化学性质。所有已知元素都被列在周期表中，每种元素都有自己独特的化学符号，例如 H 表示氢，O 表示氧。
Atoms themselves are made of subatomic particles: protons, neutrons and electrons. Protons have a positive charge (+1), neutrons have no charge, and electrons have a negative charge (−1). The nucleus at the centre of an atom contains protons and neutrons; electrons move around the nucleus in shells or energy levels.
原子本身由亚原子粒子组成：质子、中子和电子。质子带一个单位正电荷 (+1)，中子不带电，电子带一个单位负电荷 (−1)。原子中心的原子核包含质子和中子；电子在核外的电子壳层或能级上运动。
The atomic number of an element is the number of protons in its nucleus. In a neutral atom, the number of electrons equals the number of protons. For example, a carbon atom has 6 protons and therefore 6 electrons.
元素的原子序数就是其原子核中的质子数。在中性原子中，电子数等于质子数。例如，碳原子有 6 个质子，因此也有 6 个电子。
3. Compounds and Mixtures | 化合物与混合物
A compound is a substance formed when two or more different elements are chemically joined together. The properties of a compound are usually very different from the properties of the elements that make it up. For example, water (H₂O) is a liquid formed from hydrogen (a gas) and oxygen (a gas).
化合物是由两种或多种不同元素通过化学键结合而成的物质。化合物的性质通常与组成它的元素性质截然不同。例如，水 (H₂O) 是由氢（气体）和氧（气体）形成的液体。
Compounds have a fixed composition and can only be separated into their elements by chemical reactions. Common compounds include carbon dioxide (CO₂), table salt (sodium chloride, NaCl) and sulfuric acid (H₂SO₄).
化合物有固定的组成，只能通过化学反应才能分解成其组成元素。常见化合物包括二氧化碳 (CO₂)、食盐（氯化钠 NaCl）和硫酸 (H₂SO₄)。
A mixture consists of two or more substances that are not chemically combined. The components keep their own properties and can be separated by physical methods such as filtration, distillation or chromatography. Air is a mixture of gases; sea water is a mixture of water and dissolved salts.
混合物由两种或多种物质组成，但这些物质并未通过化学方式结合。各组分保持自身性质，可通过过滤、蒸馏或色谱等物理方法分离。空气是气体混合物；海水是水和溶解盐的混合物。
4. The Periodic Table | 元素周期表
The Periodic Table arranges all known elements in order of increasing atomic number. Elements are placed in rows called periods and columns called groups. Elements in the same group have similar chemical properties because they have the same number of electrons in their outermost shell.
元素周期表按原子序数递增的顺序排列所有已知元素。元素排成行（称为周期）和列（称为族）。同一族的元素化学性质相似，因为它们最外层电子数相同。
Group 1 contains the alkali metals, such as lithium (Li), sodium (Na) and potassium (K). These metals are soft, shiny and highly reactive. Group 7 elements are the halogens, including fluorine (F₂), chlorine (Cl₂) and bromine (Br₂); they are non‑metals and very reactive. Group 0 (or 8) elements are the noble gases, such as helium (He), neon (Ne) and argon (Ar); they are colourless, odourless and unreactive.
第 1 族是碱金属，如锂 (Li)、钠 (Na) 和钾 (K)。这些金属质地柔软、有光泽且非常活泼。第 7 族元素是卤素，包括氟 (F₂)、氯 (Cl₂) 和溴 (Br₂)；它们是非金属且反应性强。第 0 族（或第 8 族）元素是稀有气体，如氦 (He)、氖 (Ne) 和氩 (Ar)；它们无色、无味且不活泼。
Metals are found on the left and centre of the table, while non‑metals are on the right. A zig‑zag line separates metals from non‑metals. Hydrogen is placed at the top left, but it is a non‑metal.
金属位于周期表的左侧和中部，非金属位于右侧。一条锯齿形线将金属和非金属分开。氢位于左上角，但它属于非金属。
5. Chemical Reactions and Word Equations | 化学反应与文字方程式
A chemical reaction involves the rearrangement of atoms to form new substances. Signs of a chemical reaction include colour change, temperature change, formation of a gas (bubbles), or the appearance of a precipitate (an insoluble solid).
化学反应涉及原子重新排列形成新的物质。化学反应的迹象包括颜色变化、温度变化、气体产生（气泡）或沉淀（不溶性固体）的生成。
cts on the right. For example: magnesium + oxygen → magnesium oxide. This shows that magnesium reacts with oxygen to produce magnesium oxide.
文字方程式用来概括反应。起始物质（反应物）写在左边，接着是箭头 (→)，右边写产物。例如：镁 + 氧气 → 氧化镁。这表示镁与氧气反应生成氧化镁。
eaction of metals with acids. Combustion of carbon: carbon + oxygen → carbon dioxide (C + O₂ → CO₂).
Year 8 学习的一些重要反应包括燃烧（在氧气中燃烧）、热分解（通过加热分解化合物）以及金属与酸的反应。碳的燃烧：碳 + 氧气 → 二氧化碳 (C + O₂ → CO₂)。
6. Acids and Alkalis | 酸与碱
Acids are substances that release hydrogen ions (H⁺) when dissolved in water. They have a sour taste and can be corrosive. Common laboratory acids include hydrochloric acid (HCl), sulfuric acid (H₂SO₄) and nitric acid (HNO₃).
酸是溶于水时释放氢离子 (H⁺) 的物质。酸有酸味，可能具有腐蚀性。实验室常见酸包括盐酸 (HCl)、硫酸 (H₂SO₄) 和硝酸 (HNO₃)。
Alkalis are soluble bases that release hydroxide ions (OH⁻) in water. They feel soapy and can also be corrosive. Common alkalis include sodium hydroxide (NaOH) and potassium hydroxide (KOH). A base is a substance that can neutralise an acid; an alkali is a base that dissolves in water.
碱是可溶性碱，在水中释放氢氧根离子 (OH⁻)。碱手感滑腻，也可能具有腐蚀性。常见碱包括氢氧化钠 (NaOH) 和氢氧化钾 (KOH)。碱是能中和酸的物质；可溶于水的碱叫做 alkali。
Indicators are substances that change colour in acids and alkalis. Litmus paper turns red in an acid and blue in an alkali. Universal indicator gives a range of colours depending on the strength of the acid or alkali.
指示剂是在酸和碱中会变色的物质。石蕊试纸在酸中变红，在碱中变蓝。通用指示剂会根据溶液酸碱性的强弱显示不同的颜色。
7. The pH Scale | pH 值
The pH scale measures how acidic or alkaline a solution is. It runs from 0 to 14. A pH of 7 is neutral (pure water). Values below 7 indicate an acidic solution; the lower the pH, the stronger the acid. Values above 7 indicate an alkaline solution; the higher the pH, the stronger the alkali.
pH 值用于衡量溶液的酸碱程度，范围从 0 到 14。pH 7 呈中性（纯水）。pH 低于 7 为酸性溶液，pH 值越低，酸性越强。pH 高于 7 为碱性溶液，pH 值越高，碱性越强。
| pH range | pH 范围 | Example | 示例 | Nature | 性质 |
|---|---|---|
| 0–2 | Stomach acid (HCl) | 胃酸 (HCl) | Strong acid | 强酸 |
| 3–4 | Vinegar (ethanoic acid) | 醋 (乙酸) | Weak acid | 弱酸 |
| 7 | Pure water | 纯水 | Neutral | 中性 |
| 8–10 | Soap | 肥皂 | Weak alkali | 弱碱 |
| 13–14 | Sodium hydroxide solution | 氢氧化钠溶液 | Strong alkali | 强碱 |
When Universal Indicator is added to a solution, the colour observed can be matched to a pH colour chart. Acidic solutions give red, orange or yellow colours; neutral solutions give green; alkaline solutions give blue or violet colours.
将通用指示剂加入溶液中，观察到的颜色可与 pH 比色卡比对。酸性溶液呈红色、橙色或黄色；中性溶液呈绿色；碱性溶液呈蓝色或紫色。
8. Neutralisation | 中和反应
+ water. For example, hydrochloric acid + sodium hydroxide → sodium chloride + water (HCl + NaOH → NaCl + H₂O).
中和反应是酸和碱（或碱）反应生成盐和水的过程。一般文字方程式为：酸 + 碱 → 盐 + 水。例如，盐酸 + 氢氧化钠 → 氯化钠 + 水 (HCl + NaOH → NaCl + H₂O)。
remaining ions form the salt. This is why the pH moves towards 7 as neutralisation occurs.
在中和反应中，酸中的 H⁺ 离子与碱中的 OH⁻ 离子结合生成水分子 (H⁺ + OH⁻ → H₂O)。剩余的离子生成盐。这就是为什么随着中和反应的进行，pH 值逐渐趋向 7。
Neutralisation has many practical applications, including treating acidic soil with lime (calcium hydroxide), relieving indigestion with antacid tablets containing bases, and treating acidic waste before it is released into the environment.
中和反应在生活中有许多应用，例如用石灰（氢氧化钙）处理酸性土壤，用含碱的抗酸药片缓解胃灼热，以及在酸性废物排放到环境前进行中和处理。
9. Metals and Non‑metals | 金属与非金属
Metals are elements that are typically shiny, good conductors of heat and electricity, malleable (can be hammered into sheets) and ductile (can be drawn into wires). Most metals have high melting and boiling points and are solid at room temperature, except mercury (Hg), which is a liquid. Non‑metals usually have the opposite properties: they are dull, poor conductors (except graphite, a form of carbon), and are often brittle when solid.
金属通常具有光泽，是热和电的良导体，具有延展性（可锤打成薄片）和展性（可拉成丝）。大多数金属熔点和沸点较高，室温下为固体，但汞 (Hg) 是液体。非金属通常性质相反：暗淡无光，导电导热性差（石墨这种碳的形式除外），固体时常呈脆性。
s tend to form positive ions (cations) by losing electrons, for example Na → Na⁺ + e⁻. Non‑ lectrons, for example Cl₂ + 2e⁻ → 2Cl⁻. Metallic oxides are basic or amphoteric, while non‑metallic oxides are acidic.
化学性质也不同。金属倾向于失去电子形成正离子（阳离子），如 Na → Na⁺ + e⁻。非金属倾向于得到电子形成负离子（阴离子），如 Cl₂ + 2e⁻ → 2Cl⁻。金属氧化物呈碱性或两性，而非金属氧化物呈酸性。
- Metal examples | 金属举例: Iron (Fe), copper (Cu), aluminium (Al), gold (Au) | 铁 (Fe)、铜 (Cu)、铝 (Al)、金 (Au)
- Non‑metal examples | 非金属举例: Oxygen (O₂), sulfur (S), carbon (C), chlorine (Cl₂) | 氧气 (O₂)、硫 (S)、碳 (C)、氯气 (Cl₂)
10. Reactivity Series | 金属活动性顺序
The reactivity series is a list of metals arranged in order of how vigorously they react with water, acids and oxygen. More reactive metals are placed higher in the series. A simple reactivity series for Year 8 includes:
金属活动性顺序是按金属与水、酸及氧气反应的剧烈程度排列的顺序。越活泼的金属排在越前面。Year 8 学习的一个简单活动性顺序如下：
Potassium (K) > Sodium (Na) > Calcium (Ca) > Magnesium (Mg) > Aluminium (Al) > Zinc (Zn) > Iron (Fe) > Lead (Pb) > Copper (Cu) > Silver (Ag) > Gold (Au)
钾 (K) > 钠 (Na) > 钙 (Ca) > 镁 (Mg) > 铝 (Al) > 锌 (Zn) > 铁 (Fe) > 铅 (Pb) > 铜 (Cu) > 银 (Ag) > 金 (Au)
ith water at all. Metals above hydrogen in the series can displace hydrogen from acids, forming a salt and hydrogen gas. For example: zinc + sulfuric acid → zinc sulfate + hydrogen.
像钾和钠这样的金属与水反应非常剧烈，生成氢气和金属氢氧化物，而铜和金则完全不与水反应。排在氢前面的金属可以从酸中置换出氢气，生成盐和氢气。例如：锌 + 硫酸 → 硫酸锌 + 氢气。
ed in copper(II) sulfate solution, iron displaces copper: iron + copper sulfate → iron sulfate + copper. The blue colour of the solution fades and a brown copper coating appears.
当较活泼金属从化合物中取代较不活泼金属时，就会发生置换反应。例如，将铁钉放入硫酸铜溶液中，铁置换出铜：铁 + 硫酸铜 → 硫酸亚铁 + 铜。蓝色溶液颜色变浅，并出现红棕色的铜层。
The reactivity series also predicts extraction methods. Metals less reactive than carbon (e.g. iron, zinc) can be extracted from their ores by heating with carbon. Very reactive metals (e.g. sodium, aluminium) must be extracted by electrolysis of their molten compounds.
活动性顺序还可用于预测金属冶炼方法。活泼性低于碳的金属（如铁、锌）可通过与碳共热从其矿石中提取。非常活泼的金属（如钠、铝）必须通过电解其熔融化合物的方法提取。
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