Atoms, Elements, Compounds, and Mixtures | 原子、元素、化合物与混合物

📚 Atoms, Elements, Compounds, and Mixtures | 原子、元素、化合物与混合物

Welcome to this Edexcel IGCSE Science revision guide. We will explore the fundamental ideas of matter: what atoms are made of, how elements are arranged in the periodic table, and how we can separate mixtures in the laboratory. This topic is essential for all three sciences – biology, chemistry, and physics – and appears frequently in paper 1 and paper 2 questions.

欢迎阅读这篇 Edexcel IGCSE 科学复习指南。我们将探索物质的基本概念：原子由什么构成、元素如何排列在元素周期表中，以及我们如何在实验室中分离混合物。这个主题对生物、化学和物理三科都至关重要，在卷一和卷二考试中经常出现。

1. The Structure of an Atom | 原子结构

An atom is the smallest particle of an element that retains the properties of that element. Every atom consists of a central nucleus containing protons and neutrons, with electrons moving around the nucleus in energy levels (shells). Protons are positively charged, electrons are negatively charged, and neutrons have no charge. In a neutral atom, the number of protons equals the number of electrons.

原子是保持元素性质的最小粒子。每个原子由一个含有质子和中子的原子核构成，电子则在核外能量层（电子壳层）中运动。质子带正电荷，电子带负电荷，中子不带电。在中性原子中，质子数等于电子数。

Key facts you need to remember:

你需要记住的关键事实：

Protons and neutrons are found in the nucleus.
质子和中子位于原子核内。
Electrons occupy shells and are very light – their mass is usually ignored.
电子占据电子壳层，质量极小——通常忽略不计。
The nucleus is tiny but contains almost all the mass of the atom.
原子核很小，但几乎包含了原子的全部质量。

2. Atomic Number and Mass Number | 原子序数与质量数

The atomic number (also called proton number) is the number of protons in the nucleus. The mass number (also called nucleon number) is the total number of protons and neutrons. We write these as a standard notation, with the mass number as a superscript and the atomic number as a subscript next to the chemical symbol.

原子序数（也称质子数）是原子核中的质子数目。质量数（也称核子数）是质子和中子的总数。我们用标准记法表示：质量数作为上标，原子序数作为下标，写在化学符号旁边。

Example: ₂₄Mg or Mg-24 – mass number 24, atomic number 12

例如：₂₄Mg 或 Mg-24 —— 质量数 24，原子序数 12

In a neutral atom, the number of electrons also equals the atomic number. This means you can work out the proton and neutron numbers from these two values.

在中性原子中，电子数也等于原子序数。这意味着你可以根据这两个数值推算出质子数和中子数。

3. Isotopes | 同位素

Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. This means they have the same atomic number but different mass numbers. Because they have the same electron arrangement, isotopes show the same chemical properties. However, physical properties such as density may differ.

同位素是指同一种元素中质子数相同但中子数不同的原子。因此它们具有相同的原子序数，但质量数不同。由于同位素的电子排布相同，它们表现出相同的化学性质。然而，物理性质如密度可能不同。

A classic example is carbon: carbon-12 (₆¹²C) and carbon-14 (₆¹⁴C). Carbon-14 is radioactive and used in dating ancient objects.

一个经典的例子是碳：碳-12（₆¹²C）和碳-14（₆¹⁴C）。碳-14具有放射性，常用于测定古代物体的年代。

4. Relative Atomic Mass | 相对原子质量

Relative atomic mass (Aᵣ) is the average mass of an atom of an element compared to one twelfth of the mass of an atom of carbon-12. Because most elements naturally exist as a mixture of isotopes, the Aᵣ you see on the periodic table is a weighted average.

相对原子质量（Aᵣ）是指一种元素的原子的平均质量相对于碳-12原子质量的十二分之一的比例。由于大多数元素天然以同位素混合物形式存在，你在元素周期表中看到的Aᵣ是加权平均值。

Aᵣ = (mass of isotope 1 × abundance 1 + mass of isotope 2 × abundance 2) ÷ total abundance

Aᵣ =（同位素1的质量 × 丰度1 + 同位素2的质量 × 丰度2）÷ 总丰度

For example, chlorine has two isotopes: ³⁵Cl (75%) and ³⁷Cl (25%). Its Aᵣ is (35 × 75 + 37 × 25) ÷ 100 = 35.5.

例如，氯有两种同位素：³⁵Cl（75%）和³⁷Cl（25%）。其Aᵣ为（35 × 75 + 37 × 25）÷ 100 = 35.5。

5. The Periodic Table | 元素周期表

The periodic table arranges elements in order of increasing atomic number. Rows are called periods, and columns are called groups. Elements in the same group have the same number of outer-shell electrons, so they have similar chemical properties. Group numbers 1–7 and Group 0 are used in Edexcel IGCSE.

元素周期表按原子序数递增的顺序排列元素。横行称为周期，纵列称为族。同一族的元素具有相同的核外最外层电子数，因此化学性质相似。在 Edexcel IGCSE 中使用第1–7族和第0族。

Group 1 – alkali metals – very reactive, soft, one outer electron.
第1族——碱金属——非常活泼，质软，有一个最外层电子。
Group 2 – alkaline earth metals – less reactive than Group 1.
第2族——碱土金属——活泼性低于第1族。
Group 7 – halogens – reactive non-metals with seven outer electrons.
第7族——卤素——活性非金属，有七个最外层电子。
Group 0 – noble gases – stable, full outer shell, very unreactive.
第0族——稀有气体——稳定，最外层全满，非常不活泼。

6. Metals and Non-Metals | 金属与非金属

Metals and non-metals can be distinguished by their properties. Metals are usually shiny (lustrous), good conductors of heat and electricity, malleable (can be hammered into shape) and ductile (can be drawn into wires). Non-metals are usually dull, poor conductors (insulators), and brittle when solid.

金属和非金属可以通过性质加以区分。金属通常有光泽（光亮），是热和电的良导体，具有延展性（可以锤打成薄片）和展性（可以拉成细丝）。非金属通常暗淡无光，是不良导体（绝缘体），固态时易脆。

On the periodic table, the step line dividing metals from non-metals runs from boron (B) to polonium (Po). Elements to the left are metals; elements to the right and at the top are non-metals. Metalloids such as silicon (Si) and germanium (Ge) lie along the border.

在元素周期表中，从硼（B）到钋（Po）的阶梯线区分金属与非金属。左侧元素是金属；右侧和顶部的元素是非金属。硅（Si）和锗（Ge）等准金属位于边界附近。

7. Elements, Compounds, and Mixtures | 元素、化合物和混合物

An element is a pure substance that cannot be broken down into simpler substances by chemical methods. A compound is a substance formed when two or more elements chemically combine in fixed proportions. A mixture is made of two or more substances that are not chemically combined and can be mixed in any ratio.

元素是由同种原子组成的纯净物，不能通过化学方法分解成更简单的物质。化合物是由两种或两种以上元素按固定比例通过化学方式结合而成的物质。混合物是由两种或多种物质机械混合而成，其成分之间没有化学结合，可以按任意比例混合。

Important differences between compounds and mixtures:

化合物与混合物的重要区别：

Compound 化合物	Mixture 混合物
Fixed composition 组成固定	Variable composition 组成可变
Chemical reaction occurs 发生化学反应	No chemical reaction 无化学反应
Properties differ from the elements 性质与成分元素不同	Properties are the sum of the substances 性质是各成分性质的叠加

8. Separation Techniques | 分离方法

Mixtures can be separated using physical methods. You need to know when to use each technique.

混合物可以通过物理方法分离。你需要知道每种方法的适用情况。

Filtration – used to separate an insoluble solid from a liquid. Example: sand from water.
过滤 —— 用于分离不溶性固体和液体。例：沙子与水。
Crystallisation / evaporation – used to obtain a soluble solid from a solution. Example: salt from seawater.
结晶 / 蒸发 —— 用于从溶液中获得可溶性固体。例：从海水中制取食盐。
Simple distillation – used to separate a solvent from a solution. Example: pure water from ink.
简单蒸馏 —— 用于从溶液中分离溶剂。例：从墨水中制取纯水。
Fractional distillation – used to separate two miscible liquids with different boiling points. Example: ethanol from water.
分馏 —— 用于分离沸点不同的两种互溶液体。例：从水中分离乙醇。
Paper chromatography – used to separate dyes in a mixture, e.g., food colourings.
纸色谱法 —— 用于分离混合物中的染料，例如食用色素。

9. Chemical Symbols and Formulae | 化学符号与化学式

Each element has a unique chemical symbol. The first letter is always a capital, and if there is a second letter, it is a lowercase letter. For example: O (oxygen), Fe (iron), Na (sodium). Formulas represent the ratio of atoms in a compound. For example, CO₂ means one carbon atom and two oxygen atoms. Correct formulae are essential for balancing equations.

每种元素都有一个唯一的化学符号。第一个字母总是大写，如果有第二个字母，则用小写。例如：O（氧）、Fe（铁）、Na（钠）。化学式表示化合物中原子的比例。例如，CO₂ 表示一个碳原子和两个氧原子。正确的化学式对于配平方程式至关重要。

You also need to recall the diatomic elements: hydrogen (H₂), nitrogen (N₂), oxygen (O₂), fluorine (F₂), chlorine (Cl₂), bromine (Br₂), and iodine (I₂).

你还需要记住双原子元素：氢（H₂）、氮（N₂）、氧（O₂）、氟（F₂）、氯（Cl₂）、溴（Br₂）和碘（I₂）。

10. Common Questions and Examination Tips | 常见问题与考试技巧

In Edexcel IGCSE Science papers, you will often be asked to identify the number of subatomic particles, explain why isotopes have similar chemical properties, or choose a separation technique. Always read the question carefully and give the full reason, not just ‘because it is an isotope’.

在 Edexcel IGCSE 科学试卷中，你经常会被要求确定亚原子粒子数目、解释为什么同位素具有相似的化学性质，或者选择分离方法。请务必仔细审题，并给出完整理由，而不是只写“因为它是同位素”。

Common errors to avoid:

需要避免的常见错误：

Confusing the atomic number and mass number – remember that the atomic number tells you the protons (and electrons), not the neutrons.
混淆原子序数与质量数——记住原子序数告诉你质子数（和电子数），而不是中子数。
Writing the formula of an ionic compound incorrectly – check charges balance.
写错离子化合物的化学式——检查电荷是否平衡。
Using ‘mixture’ when you mean ‘compound’ – a compound has a chemical change, a mixture does not.
在表达“混合物”时错用“化合物”——化合物发生了化学变化，混合物没有。

Practise drawing electron shell diagrams for the first 20 elements. This will help with questions about group properties and bonding.

练习画出前20种元素的电子壳层图。这有助于回答关于族性质和化学键的问题。

11. Linking to Biology and Physics | 联系生物与物理

This topic is not only for chemistry. In biology, you need to understand the atoms in water and carbon dioxide for photosynthesis and respiration. In physics, the model of the atom is used to explain radioactivity and half-life. The same ideas of elements and compounds also explain why isotopes of uranium are used in nuclear power.

这个主题不仅仅是化学。在生物学中，你需要理解水和二氧化碳中的原子以理解光合作用和呼吸作用。在物理学中，原子模型用于解释放射性和半衰期。元素和化合物的概念也解释了为什么铀的同位素用于核电站。

Remember that Edexcel Science (Double Award) tests all three sciences together, so be ready to apply chemical concepts to biological and physical contexts.

记住，Edexcel 科学（双奖）考试将三门学科放在一起考查，因此要准备好将化学概念应用到生物和物理情境中。

12. Quick Recap and Checklist | 快速回顾与检查表

Before the exam, check that you can:

考试前，请确认你能做到：

Label a diagram of the atom, showing protons, neutrons and electrons.
标注原子示意图，显示质子、中子和电子。
Calculate the number of protons, neutrons, and electrons from a symbol notation.
根据符号表示法计算质子、中子、电子数目。
Define isotope and relative atomic mass.
定义同位素和相对原子质量。
Identify groups and periods on the periodic table.
确定元素周期表中的族和周期。
Describe the difference between an element, a compound, and a mixture.
描述元素、化合物和混合物之间的区别。
Choose the correct separation technique for a given mixture.
为给定的混合物选择合适的分离方法。

Once you have mastered these, you are ready for any question on the basics of matter in Edexcel IGCSE Science.

一旦你掌握了这些，你就能应对 Edexcel IGCSE 科学考试中任何关于物质基础的问题了。

Published by TutorHao | Science Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）

Atoms, Elements, Compounds, and Mixtures | 原子、元素、化合物与混合物