📚 Year 9 WJEC Chemistry: Key Concepts Consolidation | 九年级 WJEC 化学：核心知识点梳理
Welcome to your Year 9 WJEC Chemistry revision guide. This article summarises the essential topics you will need to master, from particle theory to energy changes. Use this resource to consolidate your understanding and prepare for assessments with confidence.
欢迎阅读九年级 WJEC 化学复习指南。本文总结了你需要掌握的核心主题，从粒子理论到能量变化。利用这份资源巩固理解，为评估做好充分准备。
1. States of Matter and the Particle Model | 物质状态与粒子模型
All matter is made up of tiny particles. The state of a substance – solid, liquid or gas – depends on how these particles are arranged and how they move.
所有物质由微小粒子组成。物质的状态——固态、液态或气态——取决于这些粒子的排列方式和运动情况。
In solids, particles are tightly packed in a regular pattern and vibrate in fixed positions. This gives solids a definite shape and volume.
在固体中，粒子紧密排列成规则图案，并在固定位置上振动。这使得固体具有固定的形状和体积。
In liquids, particles are still close together but can slide past each other. Liquids have a fixed volume but take the shape of their container.
在液体中，粒子仍然相互靠近，但能够相互滑动。液体有固定的体积，但会随容器形状改变外形。
In gases, particles are far apart and move rapidly in all directions. Gases have no fixed shape or volume and will spread out to fill any container.
在气体中，粒子相距很远，并向各个方向快速运动。气体没有固定的形状和体积，会扩散充满整个容器。
Changes of state include melting (solid to liquid), freezing (liquid to solid), boiling/evaporation (liquid to gas) and condensation (gas to liquid). These processes involve energy transfer: melting and boiling absorb energy; freezing and condensation release energy.
状态变化包括熔化（固→液）、凝固（液→固）、沸腾/蒸发（液→气）和冷凝（气→液）。这些过程涉及能量转移：熔化和沸腾吸收能量，凝固和冷凝释放能量。
Diffusion is the movement of particles from an area of higher concentration to an area of lower concentration. It is fastest in gases because particles move more freely and have more energy.
扩散是粒子从高浓度区域向低浓度区域运动的过程。在气体中扩散最快，因为气体粒子运动更自由，能量更高。
2. Atomic Structure: Protons, Neutrons and Electrons | 原子结构：质子、中子与电子
All substances are made from atoms. An atom consists of a tiny, dense nucleus surrounded by electrons that move in shells (energy levels). The nucleus contains protons and neutrons.
所有物质都由原子构成。原子由一个微小、致密的原子核和绕核运动的电子组成，电子分布在壳层（能级）中。原子核包含质子和中子。
Protons carry a positive electric charge, neutrons have no charge, and electrons carry a negative charge. The relative mass of a proton is 1, a neutron is 1, and an electron is about 1/1836.
质子带正电荷，中子不带电，电子带负电荷。质子的相对质量为1，中子的相对质量为1，电子的相对质量约为1/1836。
In a neutral atom, the number of electrons is equal to the number of protons. The atomic number (Z) is the number of protons and defines the element. The mass number (A) is the total number of protons plus neutrons.
在电中性原子中，电子数等于质子数。原子序数 (Z) 是质子数，它确定了元素种类。质量数 (A) 是质子数与中子数之和。
Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. They have the same atomic number but different mass numbers, e.g., carbon-12 and carbon-14.
同位素是同一种元素质子数相同而中子数不同的原子。它们原子序数相同，但质量数不同，例如碳-12和碳-14。
3. Electron Arrangement and the Periodic Table | 电子排布与周期表
Electrons occupy shells around the nucleus. The first shell can hold up to 2 electrons, the second up to
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