📚 Year 9 CIE Chemistry Core Knowledge Review | Year 9 CIE 化学核心知识点梳理
Welcome to this comprehensive revision guide covering the essential Year 9 CIE Chemistry topics. This article reviews key concepts such as the particle model, atomic structure, the periodic table, chemical reactions, acids and metals. Each section is presented in English followed by its Chinese translation to aid bilingual learning and support students preparing for CIE secondary science assessments.
欢迎阅读这份涵盖 Year 9 CIE 化学核心知识的全面复习指南。本文梳理了粒子模型、原子结构、周期表、化学反应、酸碱和金属等关键概念。每个小节均以英文解释配以中文翻译，旨在帮助双语学习，助力准备 CIE 中学科学考试的学生。
Use this article as a checklist rather than a story: read a section, close the page, then write down everything you remember on a blank sheet. Anything you cannot recall goes straight into your revision list. That active recall method is far more effective than re-reading notes, and it mirrors the way CIE exam questions ask you to explain, describe and compare.
请把本文当作清单而不是故事来使用：读完一节后合上页面，在空白纸上写下你能记住的所有内容。凡是回忆不出来的部分，直接列入你的复习清单。这种主动回忆法比反复阅读笔记有效得多，也更贴近 CIE 考试中"解释、描述、比较"类题目的要求。
1. States of Matter and the Particle Model | 物质状态与粒子模型
Matter exists in three main states: solid, liquid and gas. The particle model explains the arrangement and movement of particles in each state. In solids, particles are tightly packed in a fixed, regular pattern and vibrate about fixed positions. In liquids, particles are close together but can slide past one another, allowing liquids to flow and take the shape of their container. In gases, particles are far apart, move rapidly in random directions, and have no fixed volume or shape.
物质以三种主要状态存在：固态、液态和气态。粒子模型解释了各状态下粒子的排列和运动。固体中粒子紧密排列成固定而规则的图案，只能在固定位置附近振动；液体中粒子彼此靠近但可以相互滑动，因此液体能流动并呈现容器的形状；气体中粒子间距很大，向各个方向快速随机运动，没有固定的体积和形状。
The particle model is a model, not a photograph: it explains bulk behaviour such as compressibility, diffusion and expansion on heating. Gases are easily compressed because of the large empty space between particles, while solids and liquids are almost incompressible because their particles are already touching. When a substance is heated, its particles gain kinetic energy and move faster, so the substance expands.
粒子模型是一种模型而非照片：它用来解释可压缩性、扩散和受热膨胀等宏观现象。气体容易被压缩，因为粒子间有大量空隙；固体和液体几乎不可压缩，因为粒子已经彼此接触。物质受热时，粒子获得动能、运动加快，因此物质会膨胀。
- Solid: fixed shape and volume, particles in a regular lattice, vibrate only.
- Liquid: fixed volume but no fixed shape, particles slide past each other.
- Gas: no fixed shape or volume, particles far apart and fast moving.
- Diffusion is faster in gases than in liquids because gas particles move faster and are further apart.
- 固体：形状和体积固定，粒子呈规则晶格排列，只能振动。
- 液体：体积固定但无固定形状，粒子可相互滑动。
- 气体：形状和体积均不固定，粒子间距大、运动快。
- 扩散在气体中比在液体中快，因为气体粒子运动更快、间距更大。
| Property 性质 | Solid 固体 | Liquid 液体 | Gas 气体 |
| Particle spacing 粒子间距 | Very close 很近 | Close 较近 | Far apart 很远 |
| Motion 运动方式 | Vibrate 振动 | Slide 滑动 | Fast random 快速随机 |
| Compressibility 可压缩性 | Almost none 几乎不可 | Very low 很低 | High 高 |
2. Changes of State and Heating Curves | 状态变化与加热曲线
Changes of state are physical changes, not chemical reactions, because no new substance is formed and the particles themselves stay the same. Melting, boiling and evaporation are endothermic: energy is taken in to break the forces between particles. Freezing and condensation are exothermic: energy is released as particles come closer together. Sublimation is the direct change from solid to gas, as seen with iodine and dry ice.
状态变化属于物理变化而非化学反应，因为没有新物质生成，粒子本身也没有改变。熔化、沸腾和蒸发是吸热过程：需要吸收能量来克服粒子间的作用力。凝固和凝结是放热过程：粒子靠近时释放能量。升华是固体直接变为气体的过程，碘和干冰就是典型例子。
During a change of state the temperature stays constant even though heating continues, because the energy supplied is used to overcome intermolecular forces rather than to increase the average kinetic energy. This is why a heating curve shows flat plateaus at the melting point and boiling point. Pure substances melt and boil at sharp, fixed temperatures, while mixtures and impure samples melt over a range.
状态变化过程中温度保持不变，尽管仍在持续加热，因为所供给的能量用于克服分子间作用力，而不是提高平均动能。这就是加热曲线在熔点和沸点处出现水平平台的原因。纯净物在固定而明确的温度下熔化和沸腾，而混合物和不纯样品则在一定的温度范围内熔化。
Energy supplied = energy used to overcome forces ｜ 供给能量 = 克服作用力所需能量
3. Atomic Structure and Sub-atomic Particles | 原子结构与亚原子粒子
All matter is made of atoms, and each atom has a tiny, dense nucleus surrounded by electrons in shells. The nucleus contains protons and neutrons and holds almost all the mass of the atom, while electrons occupy most of the volume. Protons are positively charged, electrons are negatively charged, and neutrons are neutral. In a neutral atom the number of protons equals the number of electrons.
一切物质都由原子构成，每个原子都有一个极小、密度极高的原子核，核外电子分层排布。原子核含有质子和中子，几乎集中了原子的全部质量，而电子占据了原子的大部分体积。质子带正电，电子带负电，中子不带电。在中性原子中，质子数等于电子数。
The atomic number (proton number) identifies the element, and the mass number is the total number of protons plus neutrons. The number of neutrons can be found by subtracting the atomic number from the mass number. Electrons are arranged in shells, filling from the inside out, with the first shell holding up to 2 electrons, the second up to 8 and the third up to 8.
原子序数（质子数）决定元素种类，质量数等于质子数与中子数之和。用质量数减去原子序数即可得到中子数。电子分层排布，由内向外填充，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。
| Particle 粒子 | Relative charge 相对电荷 | Relative mass 相对质量 | Location 位置 |
| Proton 质子 | +1 | 1 | Nucleus 原子核 |
| Neutron 中子 | 0 | 1 | Nucleus 原子核 |
| Electron 电子 | −1 | 1/1840 ≈ 0 | Shells 电子层 |
Exam tip: always check whether a particle is an atom, an ion or an isotope before counting electrons. For example, Na⁺ has 11 protons and 10 electrons, while Cl⁻ has 17 protons and 18 electrons.
考试提示：在数电子之前，先判断该粒子是原子、离子还是同位素。例如 Na⁺ 有 11 个质子和 10 个电子，Cl⁻ 有 17 个质子和 18 个电子。
4. Isotopes, Electron Shells and Ions | 同位素、电子层与离子
Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons. Because they have identical electron arrangements, isotopes have the same chemical properties, but their physical properties such as density and mass differ slightly. Carbon-12, carbon-13 and carbon-14 are three common isotopes of carbon; only carbon-14 is radioactive and used for dating.
同位素是质子数相同但中子数不同的同种元素的原子。由于电子排布完全相同，同位素的化学性质相同，但密度、质量等物理性质略有差异。碳-12、碳-13 和碳-14 是碳的三种常见同位素，其中只有碳-14 具有放射性，可用于考古断代。
The relative atomic mass is a weighted average of the masses of the isotopes, taking into account their relative abundances. Elements in Group 1 lose one electron to form 1+ ions, Group 2 elements lose two electrons to form 2+ ions, and Group 7 elements gain one electron to form 1− ions. Atoms gain or lose electrons in order to achieve a stable, full outer shell like a noble gas.
相对原子质量是各同位素质量按其相对丰度计算得到的加权平均值。第 1 族元素失去 1 个电子形成 1+ 离子，第 2 族元素失去 2 个电子形成 2+ 离子，第 7 族元素获得 1 个电子形成 1− 离子。原子得失电子的目的，是获得像稀有气体那样稳定的满外层电子结构。
Relative atomic mass = Σ (isotope mass × abundance) ÷ Σ abundance
Worked example: if chlorine is 75% Cl-35 and 25% + 925) ÷ 100 = 35.5. This explains why many relative atomic masses are not whole numbers.
例题：若氯中 Cl-35 占 75%、Cl-37 占 25%，则 Ar = (35 × 75 + 37 × 25) ÷ 100 = (2625 + 925) ÷ 100 = 35.5。这就是许多元素相对原子质量不是整数的原因。
5. The Periodic Table and Group Trends | 周期表与族的变化规律
The periodic table arranges elements in order of increasing atomic number. Vertical columns are called groups and horizontal rows are called periods. Elements in the same group have the same number of outer-shell electrons, which is why they show similar chemical properties. The metallic character decreases from left to right across a period and increases down a group.
周期表按原子序数递增的顺序排列元素。竖列称为族，横行称为周期。同族元素最外层电子数相同，因此化学性质相似。金属性从左到右逐渐减弱，从上到下逐渐增强。
Group 1 (alkali metals) are soft, reactive metals that react vigorously with water to give a metal hydroxide and hydrogen. Reactivity increases down the group because the outer electron is further from the nucleus and lost more easily. Group 7 (halogens) are coloured non-metals whose reactivity decreases down the group. Group 0 (noble gases) have full outer shells, so they are chemically inert and are used in lamps and lasers.
第 1 族（碱金属）是质软、活泼的金属，能与水剧烈反应生成氢氧化物和氢气，其活泼性从上到下递增，因为最外层电子离原子核更远、更容易失去。第 7 族（卤素）是有颜色的非金属，其活泼性从上到下递减。第 0 族（稀有气体）最外层电子已排满，化学性质极不活泼，常用于灯具和激光器。
- Group number of the main groups = number of outer-shell electrons.
- Period number = number of occupied electron shells.
- Metals are on the left and centre; non-metals are on the upper right.
- 主族元素的族序数 = 最外层电子数。
- 周期序数 = 已占用电子层数。
- 金属位于左侧和中部，非金属位于右上部。
6. Chemical Bonding: Ionic, Covalent and Metallic | 化学键：离子键、共价键与金属键
Atoms bond in order to achieve a stable full outer shell. Ionic bonding occurs between metals and non-metals by transferring electrons, producing oppositely charged ions held by strong electrostatic attraction. Ionic compounds form giant lattices, have high melting and boiling points, and conduct electricity only when molten or dissolved.
原子通过成键以获得稳定的满外层结构。离子键发生在金属与非金属之间，通过电子的转移形成带相反电荷的离子，并由强静电引力相互吸引。离子化合物形成巨型晶格，熔沸点高，只有在熔融或溶解状态下才能导电。
Covalent bonding occurs between non-metals by sharing pairs of electrons. Simple molecular substances such as water, carbon dioxide and oxygen have weak forces between molecules, giving low melting and boiling points, and they do not conduct electricity. Giant covalent structures such as diamond, graphite and silicon dioxide have very high melting points because large numbers of strong covalent bonds must be broken.
共价键发生在非金属之间，通过共用电子对形成。水、二氧化碳、氧气等简单分子物质，分子间作用力较弱，因此熔沸点低，且不导电。金刚石、石墨、二氧化硅等巨型共价结构熔点极高，因为需要破坏大量强共价键。
Metallic bonding consists of positive metal ions in a sea of delocalised electrons. The delocalised electrons are free to move, which explains why metals conduct heat and electricity, and why they are malleable and ductile. Alloys such as steel and bronze are harder than pure metals because the layers of ions are distorted and cannot slide over one another easily.
金属键由浸没在自由电子海中的金属正离子构成。离域电子可以自由移动，这解释了金属为什么能导热导电，也解释了金属为什么具有延展性。钢、青铜等合金比纯金属更硬，因为离子层发生畸变，不易相互滑动。
7. Chemical Reactions, Equations and Conservation of Mass | 化学反应、方程式与质量守恒
A chemical reaction produces one or more new substances, and the products have different properties from the reactants. Evidence for a reaction includes colour change, gas production, temperature change, or the formation of a precipitate. In a chemical reaction atoms are rearranged, not created or destroyed, so mass is always conserved in a closed system.
化学反应生成一种或多种新物质，生成物的性质与反应物不同。判断反应发生的依据包括颜色变化、气体生成、温度变化或沉淀生成。化学反应中原子只是重新排列，既不会创生也不会消失，因此在封闭体系中质量总是守恒的。
mbol equations show formulae and the correct ratio of particles, and the number of atoms of each element must be equal on both sides. State symbols (s), (l), (g) and (aq) tell you the physical state of each substance.
文字方程式写出反应物和生成物的名称，例如"镁 + 氧气 → 氧化镁"。配平的符号方程式中要写出化学式以及正确的粒子比例，两边各元素的原子数目必须相等。状态符号 (s)、(l)、(g) 和 (aq) 用来标明各物质的状态。
2H₂ + O₂ → 2H₂O ｜ 2Mg + O₂ → 2MgO ｜ CaCO₃ → CaO + CO₂
- Combustion, oxidation, decomposition, displacement and neutralisation are the five reaction types to know.
- Balancing: adjust coefficients only, never change subscripts.
- Relative formula mass is used to check conservation of mass in calculations.
- 需要掌握的五大反应类型：燃烧、氧化、分解、置换和中和。
- 配平：只能调整系数，绝不能改动下标。
- 用相对式量可以检验计算中的质量守恒。
8. Acids, Bases and the pH Scale | 酸、碱与 pH 标度
Acids produce hydrogen ions (H⁺) in aqueous solution, while alkalis produce hydroxide ions (OH⁻). The pH scale runs from 0 to 14: below 7 is acidic, exactly 7 is neutral, and above 7 is alkaline. Strong acids such as hydrochloric and sulfuric acid ionise completely, whereas weak acids such as ethanoic acid ionise only partially, so they have a higher pH at the same concentration.
酸在水溶液中产生氢离子 (H⁺)，碱则产生氢氧根离子 (OH⁻)。pH 标度从 0 到 14：小于 7 为酸性，等于 7 为中性，大于 7 为碱性。盐酸、硫酸等强酸完全电离，而乙酸等弱酸只部分电离，因此在相同浓度下弱酸的 pH 更高。
Indicators are used to estimate pH: litmus turns red in acid and blue in alkali, methyl orange turns red in acid and yellow in alkali, and phenolphthalein is colourless in acid and pink in alkali. Universal indicator gives a full colour range, and a pH meter gives the most accurate reading.
指示剂用于估测 pH：石蕊在酸中变红、在碱中变蓝；甲基橙在酸中呈红色、在碱中呈黄色；酚酞在酸中无色、在碱中呈粉红色。通用指示剂可显示完整的颜色变化范围，而 pH 计能给出最精确的读数。
Acids react with metals to give a salt and hydrogen, with bases to give a salt and water, and with carbonates to give a salt, water and carbon dioxide. The test for carbon dioxide is that it turns limewater milky. Remember that acid reactions are not all the same speed: dilute acids react faster with reactive metals such as magnesium than with less reactive ones such as iron.
酸与金属反应生成盐和氢气，与碱反应生成盐和水，与碳酸盐反应生成盐、水和二氧化碳。检验二氧化碳的方法是其能使澄清石灰水变浑浊。注意：酸的反应速率并不相同，稀酸与镁等活泼金属的反应比与铁等较不活泼金属更快。
9. Neutralisation, Salts and Preparing Crystals | 中和反应、盐与晶体制备
base → salt + water. The salt formed depends on the acid used: hydrochloric acid gives chlorides, sulfuric acid gives sulfates, and nitric acid gives nitrates.
中和反应是酸与碱之间的反应，其离子方程式始终相同：H⁺ + OH⁻ → H₂O。一般文字方程式为：酸 + 碱 → 盐 + 水。生成何种盐取决于所用酸：盐酸生成氯化物，硫酸生成硫酸盐，硝酸生成硝酸盐。
To prepare a soluble salt such as copper(II) sulfate, add excess copper(II) oxide to warm dilute sulfuric acid, stir until the reaction stops, filter off the unreacted solid, and crystallise the filtrate by slow evaporation. Insoluble salts such as barium sulfate are made by precipitation: two soluble solutions are mixed and the insoluble product is filtered, washed and dried.
制备硫酸铜(II)等可溶性盐时，将过量氧化铜加入温热的稀硫酸中，搅拌至反应停止，过滤除去未反应的固体，再通过缓慢蒸发使滤液结晶。硫酸钡等不溶性盐则用沉淀法制备：把两种可溶盐溶液混合，将生成的沉淀过滤、洗涤并干燥。
HCl + NaOH → NaCl + H₂O ｜ H₂SO₄ + CuO → CuSO₄ + H₂O
- Use excess solid so that all the acid is used up.
- Filter to remove excess metal oxide or carbonate.
- Evaporate slowly, then leave to crystallise and dry with filter paper.
- 加入过量固体，确保酸全部反应完。
- 过滤除去过量的金属氧化物或碳酸盐。
- 缓慢蒸发，静置结晶，再用滤纸吸干。
10. Metals, Reactivity and Displacement | 金属、活动性与置换反应
The reactivity series ranks metals from the most reactive (potassium, sodium, calcium, magnesium, aluminium) to the least reactive (gold, platinum). A more reactive metal displaces a less reactive one from a solution of its salt. For example, putting zinc into copper(II) sulfate solution gives a pink deposit of copper and a colourless zinc sulfate solution.
金属活动性顺序把金属从最活泼（钾、钠、钙、镁、铝）排到最不活泼（金、铂）。较活泼的金属可以把较不活泼的金属从其盐溶液中置换出来。例如把锌放入硫酸铜(II)溶液中，会析出粉红色的铜，并得到无色的硫酸锌溶液。
Metals above carbon in the series are extracted by electrolysis of their molten ores, while metals below carbon can often be extracted by reduction with carbon. Metals such as potassium and sodium are stored in oil because they react rapidly with oxygen and water. Reaction with dilute acid gives a salt and hydrogen, and the speed of bubbling indicates the metal's reactivity.
活动性顺序中排在碳之前的金属，通常通过电解其熔融矿石来提取；排在碳之后的金属则常用碳还原法提取。钾、钠等金属需保存在煤油中，因为它们会迅速与氧气和水反应。金属与稀酸反应生成盐和氢气，产生气泡的快慢可反映金属的活泼性。
Zn + CuSO₄ → ZnSO₄ + Cu ｜ Mg + 2HCl → MgCl₂ + H₂
11. Rates of Reaction and Energy Changes | 反应速率与能量变化
The rate of a reaction depends on temperature, concentration or pressure, surface area of a solid reactant, and the presence of a catalyst. Increasing temperature speeds up a reaction because particles move faster and collide more frequently and with more energy. Increasing concentration or pressure and increasing surface area have similar effects, since more frequent collisions occur.
反应速率取决于温度、浓度或压强、固体反应物的表面积以及是否使用催化剂。升高温度会加快反应，因为粒子运动更快，碰撞更频繁且能量更高。增大浓度或压强、增大表面积也有类似效果，因为碰撞变得更加频繁。
A catalyst speeds up a reaction without being used up, and is written above the arrow in an equation. It works by providing an alternative pathway with a lower activation energy, so a greater proportion of collisions are successful. Enzymes are biological catalysts that work best at a specific optimum temperature and pH.
催化剂能加快反应速率而自身不被消耗，在方程式中写在箭头上方。它通过提供活化能更低的反应路径起作用，使更多碰撞成为有效碰撞。酶是生物催化剂，在特定的最适温度和 pH 下活性最高。
Exothermic reactions release energy to the surroundings and cause a temperature rise, such as combustion and neutralisation. Endothermic reactions take in energy and cause a temperature fall, such as thermal decomposition and photosynthesis. In a reaction profile diagram, the difference between reactant and product energy levels shows whether the reaction is exothermic or endothermic.
放热反应向环境释放能量，使温度升高，例如燃烧和中和反应。吸热反应吸收能量，使温度降低，例如热分解和光合作用。在反应能量图（反应焓图）中，反应物与生成物能量水平的差值可以判断反应是放热还是吸热。
12. Core Practicals and Exam Technique | 核心实验与考试技巧
You should be able to describe the purpose, method, variables and safety precautions of the main core practicals. These include measuring rates of reaction by gas collection, preparing a soluble salt, electrolysis of solutions, testing for gases, and chromatography of inks. Always state the independent variable, the dependent variable and the control variables in an investigation.
你应当能够描述主要核心实验的目的、方法、变量和安全注意事项，包括用排水或气体收集法测量反应速率、制备可溶性盐、溶液电解、气体检验以及墨水层析。在实验探究中，始终要写明自变量、因变量和控制变量。
In CIE examination questions, look at the command word first: "state" needs a short answer, "describe" needs a sequence of points, "explain" needs a reason linked to a scientific idea, and "compare" needs both similarities and differences. Show full working in calculations, always include units, and give answers to a sensible number of significant figures.
在 CIE 考试题目中，先看指令词："state"（写出）只需简短作答，"describe"（描述）需要按顺序说明要点，"explain"（解释）需要把理由与科学原理联系起来，"compare"（比较）则要同时写出相同点和不同点。计算题要写出完整步骤，务必带上单位，并把答案保留到合理数量的有效
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