Core Principles of Cambridge Lower Secondary Complete Chemistry (2nd Edition) | 剑桥初中完整化学（第二版）核心原理

📚 Core Principles of Cambridge Lower Secondary Complete Chemistry (2nd Edition) | 剑桥初中完整化学（第二版）核心原理

This article summarises the core principles covered in the Cambridge Lower Secondary Complete Chemistry Student Book (2nd Edition). Understanding these fundamentals will build a strong foundation for further study in chemistry.

本文总结了《剑桥初中完整化学学生用书（第二版）》中的核心原理。理解这些基础知识将为深入学习化学打下坚实基础。

1. The Particle Model of Matter | 物质粒子模型

All matter is made of tiny particles that are in constant motion. The way these particles are arranged and move determines whether a substance is a solid, a liquid or a gas.

所有物质都是由不断运动的微小粒子构成的。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 packed closely in a fixed, regular pattern. They vibrate but cannot move from place to place, giving solids a definite shape and volume.

在固体中，粒子紧密排列成固定的、有规律的图案。粒子只能振动，无法自由移动，因此固体有固定的形状和体积。

In a liquid, particles are still close together but are arranged randomly. They can move around each other, so a liquid has a fixed volume but takes the shape of its container.

在液体中，粒子仍然彼此靠近，但排列是无序的。粒子可以相互滑动，因此液体有固定的体积，但形状随容器而变。

In a gas, particles are far apart and move rapidly in all directions. A gas has no fixed shape or volume and can be compressed easily.

在气体中，粒子相距很远，快速地向各个方向运动。气体没有固定的形状和体积，且容易被压缩。

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2. States of Matter and Changes of State | 物质的状态与物态变化

Matter can change from one state to another when heated or cooled. These changes are physical, not chemical, because no new substances are formed.

物质在加热或冷却时可以从一种状态转变为另一种状态。这些变化属于物理变化，因为没有新物质生成。

The main changes of state include melting (solid to liquid), freezing (liquid to solid), boiling/evaporation (liquid to gas) and condensation (gas to liquid). Sublimation is the direct change from solid to gas.

主要的物态变化有熔化（固态变液态）、凝固（液态变固态）、沸腾/蒸发（液态变气态）和冷凝（气态变液态）。升华是指固态直接变为气态。

At the melting point, both solid and liquid can exist together. At the boiling point, liquid and gas coexist. The temperature stays constant during a change of state because energy is used to break or form particle arrangements, not to raise temperature.

在熔点时，固体和液体可以共存。在沸点时，液体和气体共存。物态变化期间温度保持不变，因为能量用于破坏或形成粒子排列，而不是升高温度。

Diffusion is the movement of particles from an area of higher concentration to an area of lower concentration. It occurs in liquids and gases but not in solids because their particles cannot move freely.

扩散是粒子从高浓度区域向低浓度区域运动的过程。扩散发生在液体和气体中，但不发生在固体中，因为固体粒子不能自由移动。

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3. Atoms, Elements and Compounds | 原子、元素与化合物

An atom is the smallest particle of an element that can take part in a chemical reaction. All substances are made of atoms.

原子是元素中能参与化学反应的最小粒子。所有物质都由原子构成。

An element is a pure substance made of only one type of atom. Elements cannot be broken down into simpler substances by chemical means. Examples include oxygen (O), iron (Fe) and gold (Au).

元素是由同一种原子组成的纯净物。元素不能通过化学方法分解成更简单的物质。例子有氧（O）、铁（Fe）和金（Au）。

A compound is a substance formed when two or more different elements are chemically bonded together. Compounds have different properties from their constituent elements. For instance, water (H₂O) is a compound made from hydrogen and oxygen.

化合物是由两种或两种以上不同元素通过化学键结合而成的物质。化合物的性质与其组成元素不同。例如，水（H₂O）是由氢和氧组成的化合物。

A mixture contains two or more different substances that are not chemically joined. The components of a mixture can be separated by physical methods, such as filtration or distillation.

混合物含有两种或两种以上未通过化学键结合的不同物质。混合物的组分可以通过物理方法（如过滤或蒸馏）分离。

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4. Introduction to the Periodic Table | 元素周期表入门

The periodic table arranges all known elements in order of increasing atomic number. The atomic number is the number of protons in the nucleus of an atom.

元素周期表将所有已知元素按原子序数递增的顺序排列。原子序数是原子核中质子的数量。

Vertical columns are called groups, and horizontal 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.

纵列称为族，横行称为周期。同一族的元素具有相似的化学性质，因为它们的最外层电子数相同。

For Lower Secondary, key groups include Group 1 (alkali metals), Group 7 (halogens) and Group 0 or 8 (noble gases). Metals are found on the left and centre, while non-metals are on the right.

在初中阶段，重点族包括第1族（碱金属）、第7族（卤素）和第0族或第8族（稀有气体）。金属位于左侧和中间，非金属位于右侧。

Each element is represented by a chemical symbol, usually one or two letters. The first letter is always capitalised, and the second, if present, is lowercase. For example, carbon is C, sodium is Na.

每种元素都由一个化学符号表示，通常为一或两个字母。第一个字母总是大写，第二个字母（如果有）小写。例如，碳是C，钠是Na。

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5. Writing Chemical Equations | 书写化学方程式

Chemical reactions can be represented by word equations or symbol equations. A word equation uses the names of reactants and products, while a symbol equation uses chemical formulae.

化学反应可以用文字方程式或符号方程式表示。文字方程式使用反应物和

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