📚 Cambridge Science: Elements, Compounds and Mixtures (Pages 101-120) | 剑桥科学：元素、化合物和混合物（第101-120页）
This revision article focuses on core chemistry concepts typically covered around pages 101-120 in Cambridge Science courses: elements, compounds and mixtures. Understanding these ideas helps you classify matter, predict simple chemical behaviour and answer questions on particle models, separation methods and chemical formulae.
本文聚焦剑桥科学课程中第101-120页常见的核心化学概念：元素、化合物和混合物。理解这些概念有助于你对物质进行分类、预测简单的化学行为，并解答关于粒子模型、分离方法和化学式的问题。
1. What is an Element? | 什么是元素？
An element is a pure substance made up of only one type of atom. Every atom of an element has the same number of protons in its nucleus, which determines its identity. Examples include oxygen, gold, carbon and hydrogen.
元素是由同一种原子组成的纯净物。同一种元素的每个原子核内都有相同数量的质子，这决定了元素的种类。常见的例子包括氧、金、碳和氢。
Elements cannot be broken down into simpler substances by chemical reactions. They are the building blocks of all matter, and about 118 elements are known today, arranged in the Periodic Table.
元素不能通过化学反应被分解成更简单的物质。它们是所有物质的基本组成单元，目前已知约有118种元素，排列在周期表中。
2. Symbols and the Periodic Table | 元素符号与周期表
Each element has a unique chemical symbol, usually consisting of one or two letters. The first letter is always capitalised, and the second letter, if present, is lowercase. For example, C stands for carbon, O for oxygen, Na for sodium and Fe for iron.
每种元素都有一个独特的化学符号，通常由一或两个字母组成。第一个字母始终大写，第二个字母（如果有）小写。例如，C 代表碳，O 代表氧，Na 代表钠，Fe 代表铁。
The Periodic Table arranges elements in order of increasing proton number and groups them by similar properties. Metals are found on the left and centre, while non-metals are on the right. Groups run vertically, and periods run horizontally.
周期表按质子数递增的顺序排列元素，并将性质相似的元素分组。金属位于周期表左侧和中间，非金属位于右侧。族是垂直列，周期是水平行。
3. What is a Compound? | 什么是化合物？
A compound is a pure substance formed when two or more different elements chemically combine in a fixed ratio. Compounds have properties that are often completely different from the properties of their constituent elements.
化合物是两种或两种以上不同元素以固定比例化合形成的纯净物。化合物的性质通常与其组成元素的性质完全不同。
For example, sodium is a highly reactive metal and chlorine is a poisonous gas, but when they react, they form sodium chloride (NaCl), which is common table salt and safe to eat in small amounts.
例如，钠是一种非常活泼的金属，氯是一种有毒气体，但当它们发生反应时，会生成氯化钠（NaCl），也就是常见的食盐，少量食用是安全的。
4. Chemical Formulae and Naming | 化学式与命名
A chemical formula uses symbols and subscript numbers to show the types and ratios of atoms in a compound. The subscript is written slightly below the line and indicates how many atoms of each element are present.
化学式用元素符号和下标数字来表示化合物中原子的种类和比例。下标写在符号右下角稍低处，表示该元素原子的个数。
Common examples include water H₂O, carbon dioxide CO₂ and ammonia NH₃. When naming simple compounds, the metal usually comes first, followed by the non-metal with an -ide ending, such as sodium chloride or magnesium oxide.
常见的例子包括水 H₂O、二氧化碳 CO₂ 和氨 NH₃。命名简单化合物时，通常金属名称在前，非金属名称在后并把词尾改为 -ide，例如氯化钠或氧化镁。
| Compound 化合物 | Formula 化学式 | Atoms present 原子组成 |
|---|---|---|
| Water 水 | H₂O | 2 hydrogen, 1 oxygen |
| Carbon dioxide 二氧化碳 | CO₂ | 1 carbon, 2 oxygen |
| Methane 甲烷 | CH₄ | 1 carbon, 4 hydrogen |
5. What is a Mixture? | 什么是混合物？
A mixture contains two or more substances that are not chemically combined. The substances in a mixture keep their own properties and can usually be separated by physical methods such as filtration, evaporation or distillation.
混合物含有两种或两种以上未发生化学结合的物质。混合物中的各物质保持自身性质，通常可以通过过滤、蒸发或蒸馏等物理方法进行分离。
Air is a common example of a mixture. It contains nitrogen, oxygen, argon, carbon dioxide and water vapour, all mixed together but not chemically bonded.
空气是混合物中常见的例子。它含有氮气、氧气、氩气、二氧化碳和水蒸气，它们混合在一起，但并不发生化学键合。
6. Difference Between Compounds and Mixtures | 化合物与混合物的区别
Compounds are formed by chemical reactions and have a fixed composition. Mixtures are formed by physical mixing and can have variable composition. This difference explains why compounds cannot be separated by simple physical methods, but mixtures usually can.
化合物通过化学反应形成，具有固定的组成。混合物通过物理混合形成，组成可以变化。这一区别解释了为什么化合物不能用简单的物理方法分离，而混合物通常可以。
- Compound 化合物: fixed ratio 固定比例, new properties 新性质, chemical separation needed 需化学方法分离
- Mixture 混合物: variable ratio 比例可变, substances keep own properties 各物质保持自身性质, physical separation possible 可用物理方法分离
7. Separation Techniques for Mixtures | 混合物的分离技术
Several physical techniques can separate mixtures based on differences in physical properties such as particle size, boiling point or solubility. Filtration separates an insoluble solid from a liquid, for example sand from water.
根据粒径、沸点或溶解性等物理性质的差异，可以用几种物理技术分离混合物。过滤可将不溶性固体从液体中分离出来，例如从水中分离沙子。
Distillation separates a solvent from a solution by boiling and condensing. Chromatography separates dissolved coloured substances, and evaporation can recover a dissolved solid from a solution.
蒸馏通过蒸发和冷凝将溶剂从溶液中分离出来。色谱法可以分离溶解的有色物质，蒸发则可以从溶液中回收溶解的固体。
| Method 方法 | Property used 利用的性质 | Example 例子 |
|---|---|---|
| Filtration 过滤 | Particle size 粒径 | Sand from water 沙和水 |
| Distillation 蒸馏 | Boiling point 沸点 | Pure water from salt solution 从盐溶液中获得纯水 |
| Chromatography 色谱法 | Solubility in a solvent 在溶剂中的溶解性 | Separating ink dyes 分离墨水染料 |
8. Identifying Elements and Compounds | 鉴定元素与化合物
You can often tell whether a substance is an element, a compound or a mixture by looking at its formula and its properties. A pure element has only one capital letter in its symbol, while a compound has at least two different capital letters in its formula.
通过观察物质的化学式和性质，通常可以判断它是元素、化合物还是混合物。纯元素的符号只有一个大写字母，而化合物的化学式中至少有两个不同的大写字母。
However, some elements exist as diatomic molecules such as O₂, N₂ and Cl₂. These are still elements because only one type of atom is present, even though there are two atoms in the molecule.
但有些元素以双原子分子形式存在，如 O₂、N₂ 和 Cl₂。它们仍然是元素，因为分子中只有一种原子，尽管分子中有两个原子。
9. Everyday Examples and Applications | 日常实例与应用
Elements, compounds and mixtures are everywhere in daily life. The oxygen you breathe is an element, the water you drink is a compound, and the air around you is a mixture.
元素、化合物和混合物在日常生活中随处可见。你呼吸的氧气是元素，喝的水是化合物，周围的空气是混合物。
Understanding these classifications helps in real-world industries such as water purification, pharmaceutical manufacturing and food testing. For example, chromatography is used to check food colourings, and distillation is used to produce clean drinking water.
理解这些分类有助于现实中的行业，如水净化、制药和食品检测。例如，色谱法用于检测食品着色剂，蒸馏用于生产干净的饮用水。
10. Summary and Exam Tips | 总结与考试技巧
To succeed in Cambridge Science questions on this topic, remember the definitions clearly: an element contains one type of atom, a compound contains two or more different elements chemically combined, and a mixture contains substances that are not chemically joined.
要在剑桥科学考试中答好本专题的题目，请牢记定义：元素只含一种原子，化合物由两种或两种以上不同元素化合而成，混合物中的物质没有发生化学结合。
When writing formulae, use correct subscripts and capital letters. When describing separation, link the technique to the physical property being used. Always give examples to support your answers where possible.
书写化学式时，使用正确的下标和大写字母。描述分离时，要把技术与所利用的物理性质联系起来。在可能的情况下，始终举出例子来支持你的答案。
Published by TutorHao | Cambridge Science Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导