📚 Year 8 WJEC Chemistry: Core Knowledge Review | Year 8 WJEC 化学：核心知识点梳理
In Year 8 WJEC Chemistry, students build a solid foundation by exploring the particle nature of matter, atomic structure, and the differences between elements, compounds and mixtures. They learn to write simple chemical equations, investigate acids and alkalis, and master key separation techniques. The curriculum also introduces Earth chemistry, including rocks, the rock cycle and the atmosphere, alongside essential laboratory safety. This article organises all the core knowledge into clear, bilingual sections to help you revise effectively.
在 WJEC 八年级化学课程中，学生将通过探究物质的粒子本质、原子结构以及元素、化合物与混合物的区别打下坚实基础。他们还会学习书写简单的化学方程式、研究酸和碱的性质，并掌握重要的分离技术。课程还涉及地球化学，包括岩石、岩石循环和大气层，以及必要的实验室安全。本文将所有核心知识点整理成清晰的双语小节，帮助你高效复习。
1. Particles and States of Matter | 粒子与物质状态
All matter is made of tiny, constantly moving particles. The arrangement and movement of these particles determine whether a substance is a solid, a liquid or a gas.
所有物质都由不断运动的微小粒子组成。这些粒子的排列方式和运动状态决定了物质是固体、液体还是气体。
In a solid, particles are tightly packed in a regular pattern. They can only vibrate about fixed positions, which gives a solid a definite shape and a fixed volume.
在固体中，粒子紧密堆积，排列规则。它们只能在固定位置附近振动，因此固体具有确定的形状和固定的体积。
In a liquid, particles are still close together but are arranged randomly. They can slide past one another, so a liquid has a fixed volume but takes the shape of the bottom of its container.
在液体中，粒子依然彼此靠近，但排列不规则。它们可以相互滑动，因此液体有固定体积，但会呈现容器底部的形状。
In a gas, particles are far apart and move very rapidly in all directions. Gases have no fixed shape or volume, spread out to fill any container, and can easily be compressed.
在气体中，粒子相距很远，并以很高的速度向各个方向运动。气体没有固定的形状和体积，会扩散充满整个容器，而且很容易被压缩。
The particle model helps explain why solids cannot flow, why liquids can be poured, and why gases are invisible and diffuse quickly.
粒子模型有助于解释为什么固体不能流动、液体可以被倒出以及气体不可见且迅速扩散的原因。
2. Changes of State and Diffusion | 状态变化与扩散
Melting is the change from solid to liquid when a substance is heated. Particles gain energy, vibrate more strongly and eventually break free from their fixed positions.
熔化是加热时固体变为液体的过程。粒子获得能量，振动加剧，最终挣脱固定位置。
Boiling (or evaporation) turns a liquid into a gas. Particles at the surface or throughout the liquid gain enough energy to overcome the attractions holding them together and escape into the air.
沸腾（或蒸发）使液体变为气体。液体表面或内部的粒子获得足够能量，克服彼此间的吸引力，逸散到空气中。
Condensation is the reverse process—a gas changes into a liquid when it cools. The particles lose energy and move closer together.
凝结是相反的过程——气体冷却时变为液体。粒子失去能量，彼此靠近。
Freezing occurs when a liquid turns into a solid. Particles slow down and settle into a regular pattern.
凝固是液体变为固体的过程。粒子运动减慢，并排列成规则的图案。
Sublimation is when a solid changes directly into a gas (e.g. solid carbon dioxide or iodine), and deposition is the direct change from gas to solid. These processes skip the liquid state.
升华是固体直接变为气体（如固体二氧化碳或碘），凝华则是气体直接变为固体。这些过程跳过了液态。
Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration. It happens in liquids and gases and is faster at higher temperatures because particles have more kinetic energy.
扩散是粒子从高浓度区域向低浓度区域的净运动。它发生在液体和气体中，温度越高扩散越快，因为粒子具有更大的动能。
3. Atomic Structure | 原子结构
Everything is built from atoms, the smallest particle of an element that can take part in a chemical reaction. Atoms are far too small to see; the scanning tunnelling microscope can image them.
一切物质都由原子构成，原子是元素参与化学反应的最小粒子。原子极其微小，扫描隧道显微镜可以对其进行成像。
An atom consists of a tiny, dense nucleus containing protons and neutrons, surrounded by electrons that move in energy levels (shells). Protons have a positive charge (+1), electrons have a negative charge (−1), and neutrons carry no charge.
原子由一个极其微小、致密的原子核组成，核内包含质子和中子，核外是电子在能级（壳层）中运动。质子带正电荷（+1），电子带负电荷（−1），中子不带电。
The atomic number is the number of protons in an atom. All atoms of a given element have the same atomic number. The mass number is the total number of protons and neutrons in the nucleus.
原子序数是原子中质子的数目。同一种元素的所有原子具有相同的原子序数。质量数是原子核中质子数和中子数的总和。
A neutral atom has equal numbers of protons and electrons, so the overall charge is zero. Ions form when atoms gain or lose electrons.
中性原子的质子数和电子数相等，因此总电荷为零。当原子得到或失去电子时，就会形成离子。
4. Elements, Compounds & Mixtures | 元素、化合物与混合物
An element consists of only one type of atom. Elements are listed on the Periodic Table and are represented by unique chemical symbols, such as O for oxygen, Fe for iron and Na for sodium.
元素只包含一种原子。所有元素都列在周期表中，并用独特的化学符号表示，如氧用 O、铁用 Fe、钠用 Na。
A compound contains two or more different elements chemically combined in fixed proportions. The atoms are held together by chemical bonds, and the compound has properties completely different from its constituent elements. For example, water (H₂O) is a liquid at room temperature, yet it is composed of hydrogen and oxygen gases.
化合物由两种或两种以上不同元素按固定比例通过化学键结合而成。化合物的性质与其组成元素完全不同。例如，水（H₂O）在室温下是液体，却由氢气和氧气组成。
A mixture consists of two or more substances (elements or compounds) that are not chemically combined. The components retain their individual properties and can often be separated by physical means like filtration or distillation.
混合物由两种或多种物质（元素或化合物）物理混合而成，各组分保持不变，且通常可通过过滤或蒸馏等物理方法分离。
Real-world examples: air is a mixture of gases; table salt (NaCl) is a compound; iron filings and sulfur powder can form a mixture.
实际例子：空气是气体混合物；食盐（NaCl）是化合物；铁屑和硫粉可以组成混合物。
5. The Periodic Table | 元素周期表
The modern Periodic Table arranges elements in order of increasing atomic number. Vertical columns are called groups, and horizontal rows are called periods.
现代周期表按原子序数递增的顺序排列元素。纵列称为族，横行称为周期。
Metals are found on the left and centre of the table; non-metals are on the right. Elements in the same group have similar chemical properties because they have the same number of outer-shell electrons.
金属位于周期表的左侧和中部，非金属在右侧。同一族元素化学性质相似，因为它们最外层电子数相同。
Group 1 contains the alkali metals (e.g. lithium, sodium, potassium). They are soft, highly reactive with water, and are stored under oil. Group 7 contains the halogens (e.g. fluorine, chlorine, bromine), which are reactive non-metals. Group 0 (or 8) contains the noble gases (e.g. helium, neon, argon), which are unreactive because they have a full outer shell.
第 1 族是碱金属（如锂、钠、钾），它们质地柔软，与水反应剧烈，需保存在油中。第 7 族是卤素（如氟、氯、溴），为活泼的非金属。第 0 族（或第 8 族）是稀有气体（如氦、氖、氩），由于具有满壳层电子结构，化学性质非常稳定。
The table helps predict how elements behave, such as reactivity trends—going down Group 1, reactivity increases, while in Group 7, reactivity decreases down the group.
周期表有助于预测元素的行为，比如反应性变化趋势：沿第 1 族向下，活泼性增强；沿第 7 族向下，活泼性则减弱。
6. Chemical Reactions & Equations | 化学反应与方程式
In a chemical reaction, reactants turn into products. Atoms are rearranged, but no atoms are created or destroyed. This is the law of conservation of mass.
在化学反应中，反应物变成产物。原子重新组合，但没有原子被创造或毁灭。这就是质量守恒定律。
s the names of reactants and products, for instance: magnesium + oxygen → magnesium oxide.
文字方程式用名称表示反应物和产物，例如：镁 + 氧气 → 氧化镁。
s: 2Mg + O₂ → 2MgO. The large numbers (coefficients) show the ratio of molecules involved.
配平的符号方程式使用化学式，并使两边的原子数目相等。上述反应变为：2Mg + O₂ → 2MgO。其中的大数字（化学计量数）表示参与反应的分子的比例。
ic acid + sodium hydroxide → sodium chloride + water, written as: HCl + NaOH → NaCl + H₂O.
另一个例子：盐酸 + 氢氧化钠 → 氯化钠 + 水，写作：HCl + NaOH → NaCl + H₂O。
Signs of a chemical reaction include colour change, temperature change, gas production (bubbles), and the formation of a precipitate (an insoluble solid).
化学反应的迹象包括颜色变化、温度变化、产生气体（气泡）以及生成沉淀（不溶性固体）。
7. Acids, Alkalis & Neutralisation | 酸、碱与中和反应
Acids are substances that release hydrogen ions (H⁺) in water. Common laboratory acids include hydrochloric acid (HCl), sulfuric acid (H₂SO₄) and nitric acid (HNO₃). They taste sour and can be corrosive.
酸是在水中释放氢离子（H⁺）的物质。实验室常见酸有盐酸（HCl）、硫酸（H₂SO₄）和硝酸（HNO₃）。它们有酸味，可能具有腐蚀性。
Bases and alkalis: a base neutralises an acid; an alkali is a soluble base that releases hydroxide ions (OH⁻) in water. Examples are sodium hydroxide (NaOH) and potassium hydroxide (KOH).
碱与可溶性碱：碱能中和酸；可溶性碱是在水中释放氢氧根离子（OH⁻）的物质，例如氢氧化钠（NaOH）和氢氧化钾（KOH）。
The pH scale measures how acidic or alkaline a solution is. It ranges from 0 (very acidic) to 14 (very alkaline), with 7 being neutral. Universal indicator or a pH probe can be used to measure pH.
pH 标度用于衡量溶液的酸碱度。范围从 0（强酸性）到 14（强碱性），7 为中性。可以用通用指示剂或 pH 计测量 pH。
Indicators change colour in acids and alkalis. Litmus turns red in acid and blue in alkali. Universal indicator shows a rainbow of colours: red-orange-yellow for acids, green for neutral, blue-purple-violet for alkalis.
指示剂在酸和碱中会变色。石蕊遇酸变红，遇碱变蓝。通用指示剂呈现彩虹色：酸性为红—橙—黄，中性为绿色，碱性为蓝—紫—紫色。
ater. For example, HCl + NaOH → NaCl + H₂O. This reaction releases heat and is exothermic.
中和反应是酸与碱作用生成盐和水的过程：酸 + 碱 → 盐 + 水。例如，HCl + NaOH → NaCl + H₂O。该反应放热，属于放热反应。
8. Separation Techniques | 分离技术
Mixtures can be separated by physical methods without chemical reactions. The choice of technique depends on the physical properties of the substances, such as particle size, solubility and boiling point.
混合物可以通过物理方法分离，无需化学反应。选择哪种技术取决于物质的物理性质，如粒径、溶解度和沸点。
Filtration separates an insoluble solid from a liquid. For example, sand can be separated from water using filter paper; the sand remains as residue, and the water passes through as the filtrate.
过滤用于分离不溶性固体和液体。例如，用滤纸可将沙子从水中分离；沙子作为残渣留在滤纸上，水则透过成为滤液。
Evaporation removes a soluble solid from a solution. Salt can be obtained from salt water by heating the solution until the water evaporates, leaving salt crystals behind.
蒸发可将可溶性固体从溶液中分离。将盐水加热，使水蒸发，便可得到食盐晶体。
Distillation separates a solvent from a solution by boiling and condensing. Simple distillation is used to obtain pure water from seawater: water boils, steam travels to the condenser, cools back into liquid, and is collected as distillate.
蒸馏通过沸腾和冷凝将溶剂从溶液中分离。简单蒸馏可用于从海水获得纯水：水沸腾，蒸汽进入冷凝管，冷却变回液体，作为蒸馏液被收集。
Chromatography separates mixtures of soluble substances based on their different affinities for a stationary phase and a solvent. Paper chromatography can separate the dyes in an ink: the dyes travel different distances up the paper.
色谱法根据不同物质对固定相和溶剂的亲和力差异，分离可溶性混合物。纸色谱可分离墨水中的染料：不同染料在纸上爬升的距离不同。
9. Earth Chemistry: Rocks & the Rock Cycle | 地球化学：岩石与岩石循环
Rocks are classified into three main types based on how they form. Igneous rocks form when magma or lava cools and solidifies. If magma cools slowly underground, large crystals form (e.g. granite). If lava cools quickly on the surface, crystals are small (e.g. basalt).
根据形成方式，岩石可分为三大类。火成岩由岩浆或熔岩冷却凝固形成。若岩浆在地下缓慢冷却，则形成大晶体（如花岗岩）；若熔岩在地表快速冷却，晶体则较小（如玄武岩）。
Sedimentary rocks form from sediments—rock fragments, mineral grains or remains of living things—that are compressed over millions of years. Limestone is formed from shells and skeletons; sandstone is compressed sand grains. They often contain fossils and show visible layers.
沉积岩由沉积物（岩石碎片、矿物颗粒或生物遗骸）经过数百万年的压实作用形成。石灰岩由贝壳和骨骼形成；砂岩是压实的砂粒。它们常含有化石，并有明显的层理。
Metamorphic rocks are formed when existing rocks are changed by extreme heat and pressure deep within the Earth. Marble is formed from limestone; slate is formed from shale. The minerals recrystallise without melting.
变质岩是原有岩石在地球深处受到高温高压作用发生变质而形成。大理石由石灰岩变质而来；板岩由页岩变质而来。矿物重新结晶，但并不熔化。
The rock cycle describes how rocks change from one type to another through processes such as weathering, erosion, deposition, compaction, melting and crystallisation. It operates over geological timescales and shows that Earth materials are constantly recycled.
岩石循环描述了岩石如何通过风化、侵蚀、沉积、压实、熔融和结晶等过程从一种类型转变为另一种类型。它在地质时间尺度上运行，表明地球上的物质在不断循环。
10. The Atmosphere & Climate Change | 大气与气候变化
Earth's atmosphere is a mixture of gases: around 78% nitrogen (N₂), 21% oxygen (O₂), 0.9% argon, and small amounts of carbon dioxide (CO₂), water vapour (H₂O) and other gases.
地球大气层是气体混合物：约 78% 氮气（N₂），21% 氧气（O₂），0.9% 氩气，以及少量二氧化碳（CO₂）、水蒸气（H₂O）和其他气体。
Carbon dioxide, methane and water vapour are greenhouse gases. They trap heat in the atmosphere through the natural greenhouse effect, keeping Earth warm enough for life. However, human activities such as burning fossil fuels, deforestation and agriculture have increased the concentration of these gases, enhancing the greenhouse effect and leading to global warming.
二氧化碳、甲烷和水蒸气是温室气体。它们通过自然的温室效应将热量留在大气层中，使地球保持适合生命生存的温度。然而，人类活动如燃烧化石燃料、砍伐森林和农业生产增加了这些气体的浓度，加剧了温室效应，导致全球变暖。
Evidence for climate change includes rising average global temperatures, melting ice sheets and glaciers, more frequent extreme weather events, and rising sea levels. Reducing carbon footprints by using renewable energy, recycling and planting trees can help.
气候变化的证据包括全球平均
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