📚 Year 7 WJEC Chemistry: Summer Prep & Bridging Course | Year 7 WJEC 化学：暑期预习与衔接课程
Welcome to your Year 7 WJEC Chemistry Summer Prep Course! This guide will help you explore the fascinating world of chemistry before the term begins. You will discover what everything is made of, why reactions happen, and how chemists work safely. Whether you are excited about experiments or curious about atoms, this bridging course will build your confidence and spark your interest. Let's get started!
欢迎来到七年级 WJEC 化学暑期预习课程！本指南将帮助你在学期开始前探索迷人的化学世界。你将发现万物由何构成，为什么发生反应，以及化学家如何安全工作。无论你期待动手实验还是对原子感到好奇，这门衔接课程都将建立你的信心并激发你的兴趣。我们开始吧！
1. Welcome to Chemistry | 欢迎来到化学世界
Chemistry is the branch of science that studies matter, its properties, and how it turns into new substances. Everything you touch, breathe or eat involves chemistry. From the air you inhale to the water you drink, chemical principles explain the world around you.
化学是研究物质、它的性质以及它如何转变为新物质的科学分支。你所接触、呼吸或吃的一切都与化学有关。从你吸入的空气到你喝的水，化学原理都在解释你身边的世界。
Cooking, cleaning and even the batteries in your remote control rely on chemical reactions. Your mobile phone, the fuel in a car and the digestion of food all run on chemistry. By learning chemistry you will understand the 'why' behind everyday phenomena.
烹饪、清洁，甚至遥控器里的电池都依赖化学反应。你的手机、汽车里的燃料和食物的消化都依靠化学运行。通过学习化学，你将理解日常现象背后的 '为什么'。
In Year 7 you will develop skills such as observing, predicting, measuring and drawing conclusions. Remember, being a good chemist means asking questions and staying curious! You will also learn how to record results clearly and how to explain what your evidence shows.
在七年级，你将培养观察、预测、测量和得出结论等技能。记住，成为一名好的化学家意味着不断提问、保持好奇！你还将学习如何清楚记录结果，以及如何解释你的证据说明了什么。
WJEC is the examination board used in Wales, and its science specifications build skills gradually from Year 7 towards GCSE. This summer course is not about memorising everything; it is about meeting the big ideas early so that September feels familiar, friendly and much less frightening.
WJEC 是威尔士使用的考试局，它的科学考纲从七年级到 GCSE 逐步培养能力。这个暑期课程不是要你背下所有内容，而是让你提前认识这些大概念，让九月开学时感到熟悉、亲切，也不再那么令人紧张。
2. What Everything Is Made Of: Particles and States of Matter | 万物由什么构成：粒子与物质状态
All matter is made of tiny particles. In a solid, the particles are packed closely in a regular arrangement and can only vibrate. In a liquid, the particles are still close together but arranged randomly and can slide past each other. In a gas, the particles are far apart, move quickly and randomly, and fill any container.
所有物质都由微小的粒子构成。在固体中，粒子紧密排列成规则结构，只能振动。在液体中，粒子依然靠得很近，但排列无序，可以相互滑动。在气体中，粒子相距很远，运动快速且无规则，能充满任何容器。
Substances change state when they gain or lose energy. Melting, boiling and evaporation need energy in; freezing and condensing release energy out. These changes are physical, so no new substance is made - the particles simply rearrange.
当物质获得或失去能量时，状态会改变。熔化、沸腾和蒸发需要吸收能量；凝固和凝结会释放能量。这些变化都是物理变化，没有新物质生成，只是粒子的排列方式改变了。
solid → liquid → gas (melting, boiling) ⇌ gas → liquid → solid (condensing, freezing)
Diffusion is the spreading of particles from a place of high concentration to a place of low concentration. That is why the smell of perfume crosses a room, and why a drop of ink colours a whole beaker of water without any stirring.
扩散是指粒子从高浓度区域向低浓度区域散开。这就是香水的气味能飘满整个房间的原因，也是一滴墨水不用搅拌就能把整杯水染上颜色的原因。
| State | Particle arrangement | Movement | Shape and volume |
| Solid | Close, regular | Vibrate only | Fixed shape, fixed volume |
| Liquid | Close, random | Slide past each other | Takes the shape of the container, fixed volume |
| Gas | Far apart, random | Fast and random | Fills the container, volume not fixed |
The particle model is a model, not a photograph. It does not show that particles have their own size, that forces exist between them, or that atoms contain even smaller parts. Good scientists always know the limits of the models they use.
粒子模型是一个模型，而不是一张照片。它没有显示粒子本身的大小、粒子之间的作用力，也没有显示原子内部还有更小的部分。优秀的科学家始终清楚自己所用模型的局限。
3. Atoms, Elements, Compounds and Mixtures | 原子、元素、化合物与混合物
An atom is the smallest part of an element that can exist. Atoms have a tiny central nucleus containing protons and neutrons, surrounded by electrons. Protons are positive, electrons are negative, and neutrons have no charge.
原子是元素能够存在的最小部分。原子有一个很小的中心原子核，核内有质子和中子，核外有电子。质子带正电，电子带负电，中子不带电。
An element contains only one type of atom, such as iron, oxygen or copper. A compound contains two or more different elements chemically joined together in fixed proportions, such as water (H₂O) or carbon dioxide (CO₂). A mixture contains two or more substances that are not chemically joined, so the proportions can vary.
元素只含有一种原子，例如铁、氧或铜。化合物含有两种或更多不同元素，它们以固定比例化学结合，例如水（H₂O）或二氧化碳（CO₂）。混合物含有两种或更多没有化学结合的物质，因此比例可以变化。
Chemists use symbols and formulae as a short international language. The small numbers written after a symbol tell you how many atoms of that element are in one unit of the substance.
化学家用符号和化学式作为一种简短的国际化语言。写在符号后面的小数字告诉你，一个单位物质中含有多少个该元素的原子。
- H₂O - water: 2 hydrogen atoms and 1 oxygen atom | H₂O - 水：2 个氢原子和 1 个氧原子
- CO₂ - carbon dioxide: 1 carbon atom and 2 oxygen atoms | CO₂ - 二氧化碳：1 个碳原子和 2 个氧原子
- NaCl - sodium chloride: 1 sodium atom and 1 chlorine atom | NaCl - 氯化钠：1 个钠原子和 1 个氯原子
- CH₄ - methane: 1 carbon atom and 4 hydrogen atoms | CH₄ - 甲烷：1 个碳原子和 4 个氢原子
| Substance | Element, compound or mixture? | Reason |
| Oxygen gas | Element | Only oxygen atoms present |
| Sea water | Mixture | Water and dissolved salts, not joined |
| Carbon dioxide | Compound | Carbon and oxygen chemically joined |
Two atoms of the same element joined together, such as O₂ or H₂, are called molecules. Remember that a molecule can also be a compound, for example H₂O, because it contains more than one element.
同种元素的两个原子结合在一起，例如 O₂ 或 H₂，叫做分子。记住，分子也可以是化合物，例如 H₂O，因为它含有不止一种元素。
4. Meet the Periodic Table | 认识元素周期表
The periodic table arranges all known elements in order of increasing atomic number. The columns are called groups and the rows are called periods. Elements in the same group have similar chemical properties because they have the same number of electrons in their outer shell.
元素周期表按原子序数递增的顺序排列所有已知元素。竖列称为族，横行称为周期。同一族的元素化学性质相似，因为它们最外层电子数相同。
atomic number = number of protons = number of electrons in a neutral atom
Metals are found on the left and in the centre of the table; non-metals are on the right. Metals usually conduct electricity, are shiny and malleable, while non-metals are often dull, brittle and poor conductors.
金属位于周期表的左侧和中间，非金属位于右侧。金属通常能导电、有光泽、有延展性；非金属往往颜色暗淡、易碎、导电性差。
- Group 1 - alkali metals: soft, reactive, react with water | 第 1 族 - 碱金属：柔软、活泼，与水反应
- Group 7 - halogens: reactive non-metals such as chlorine | 第 7 族 - 卤素：如氯气这样的活泼非金属
- Group 0 - noble gases: unreactive, used in lamps and balloons | 第 0 族 - 稀有气体：不活泼，用于灯具和气球
Dmitri Mendeleev produced an early version of the table in 1869. He left gaps for elements that had not yet been discovered and predicted their properties, which is one reason his table was eventually accepted.
门捷列夫在 1869 年提出了早期版本的周期表。他为尚未被发现的元素留出空位，并预测了它们的性质，这也是他的周期表最终被接受的原因之一。
5. Physical Changes and Chemical Changes | 物理变化与化学变化
A physical change alters the appearance or state of a substance but does not make a new substance. Melting ice, dissolving sugar and cutting paper are physical changes, and they are usually easy to reverse.
物理变化改变物质的外观或状态，但不会生成新物质。冰融化、糖溶解、剪纸都是物理变化，它们通常容易逆转。
A chemical change produces one or more new substances with different properties. Burning, rusting and baking are chemical changes, and they are usually difficult to reverse.
化学变化会生成一种或多种性质不同的新物质。燃烧、生锈和烘焙都是化学变化，它们通常难以逆转。
Look for the signs of a chemical reaction: a gas is given off, a colour change occurs, the temperature changes without heating, a solid precipitate forms, or light and sound are produced. One sign alone is not proof, but several together is strong evidence.
请留意化学反应的迹象：放出气体、颜色改变、没有加热却温度变化、生成固体沉淀，或者产生光和声音。单独一个迹象不算证据，但几个同时出现就是有力证据。
2H₂ + O₂ → 2H₂O
Mass is conserved in a chemical reaction. In the equation above, four hydrogen atoms and two oxygen atoms are present before and after the reaction, so nothing has been lost - it has only been rearranged.
化学反应中质量守恒。在上面的方程式中，反应前后都各有四个氢原子和两个氧原子，所以没有任何东西消失，只是重新排列了。
| Feature | Physical change | Chemical change |
| New substance formed? | No | Yes |
| Usually reversible? | Yes | No |
| Example | Boiling water | Burning magnesium |
6. Reactions Around You: Acids, Alkalis and pH | 身边的反应：酸、碱与 pH 值
Acids are substances that produce hydrogen ions, H⁺, in water. 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.
酸是在水中产生氢离子 H⁺ 的物质。碱在水中产生氢氧根离子 OH⁻。pH 标度从 0 到 14：低于 7 为酸性，正好 7 为中性，高于 7 为碱性。
Indicators tell you whether a solution is acidic or alkaline. Litmus turns red in acid and blue in alkali, while universal indicator shows a rainbow of colours that match the pH number. A pH meter gives a more precise reading.
指示剂可以告诉你溶液是酸性还是碱性。石蕊遇酸变红、遇碱变蓝，而通用指示剂会显示与 pH 数值对应的彩虹色。pH 计能给出更精确的读数。
Neutralisation happens when an acid reacts with an alkali to form a salt and water. This reaction is used in indigestion tablets, in treating soil, and in cleaning up acid spills.
中和反应发生在酸与碱反应生成盐和水的时候。这一反应被用于抗酸胃药、改良土壤以及处理酸液泄漏。
HCl + NaOH → NaCl + H₂O
Acids also react with metals to give a salt and hydrogen, and with metal carbonates to give a salt, water and carbon dioxide. You can test for hydrogen with a lit splint, which gives a squeaky pop, and for carbon dioxide with limewater, which turns cloudy.
酸还能与金属反应生成盐和氢气，与金属碳酸盐反应生成盐、水和二氧化碳。你可以用点燃的木条检验氢气，会听到爆鸣声；用石灰水检验二氧化碳，石灰水会变浑浊。
- Everyday acids: lemon juice, vinegar, stomach acid, fizzy drinks | 日常的酸：柠檬汁、醋、胃酸、碳酸饮料
- Everyday alkalis: soap, toothpaste, baking powder, bleach | 日常的碱：肥皂、牙膏、发酵粉、漂白剂
7. Separating Mixtures | 混合物的分离
Because the substances in a mixture are not chemically joined, they can be separated using physical methods. Choosing the right method depends on the properties of the substances involved, such as particle size, boiling point or solubility.
由于混合物中的物质没有化学结合，可以用物理方法将它们分离。选择哪种方法取决于物质的性质，例如颗粒大小、沸点或溶解性。
Filtration separates an insoluble solid from a liquid using filter paper and a funnel. The solid left behind is the residue and the liquid that passes through is the filtrate. Evaporation or crystallisation then recovers a dissolved solid from its solution.
过滤利用滤纸和漏斗将不溶性固体与液体分开。留在滤纸上的固体叫滤渣，穿过滤纸的液体叫滤液。蒸发或结晶则可以把溶解的固体从溶液中回收。
Simple distillation separates a solvent from a solution by boiling and condensing it. Fractional distillation separates liquids with different boiling points, and is used to separate the gases in air and the fractions of crude oil.
简单蒸馏通过沸腾和冷凝把溶剂从溶液中分离出来。分馏可以分离沸点不同的液体，用于分离空气和原油中的各馏分。
Chromatography separates dissolved substances such as the dyes in ink or food colouring. The different dyes travel up the paper at different speeds, so they appear as separate spots.
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