📚 Atoms: The Building Blocks of Matter | 原子：物质的构建基石
Welcome to this KS3 Chemistry revision guide on atoms. Atoms are the tiny building blocks that make up everything around you, from the air you breathe to the screen you are reading. Understanding atoms is the first step to explaining how elements, compounds, and chemical reactions work. This guide breaks down the core ideas you need for Key Stage 3, with clear examples and simple models.
欢迎阅读本 KS3 化学原子复习指南。原子是构成你周围一切物质的微小构建基石，从你呼吸的空气到正在阅读的屏幕。理解原子是解释元素、化合物和化学反应如何运作的第一步。本指南将带你梳理关键阶段3需要掌握的核心概念，配以清晰的例子和简单的模型。
1. What Is an Atom? | 什么是原子？
0⁻¹⁰ metre. Everything you can touch, see, or smell is made of atoms, either as single atoms or joined together.
原子是元素中能参与化学反应的最小部分。原子本身由更小的粒子组成，即质子、中子和电子。如果你能看到一个原子，它会小得惊人：一个典型原子的直径约为0.1纳米，即1 × 10⁻¹⁰米。你能触摸、看到或闻到的一切都由原子构成，要么是单个原子，要么是原子结合在一起。
2. The Particle Model of Matter | 物质的粒子模型
In KS3 science, we model matter as tiny particles. In solids, these particles are packed closely in fixed positions and only vibrate. In liquids, particles are close together but can move past each other. In gases, particles are far apart and move quickly in all directions. For elements, the particles are atoms; for compounds, the particles are molecules or ions. The particle model helps explain melting, boiling, diffusion, and pressure.
在 KS3 科学中，我们把物质模型化为微小粒子。在固体中，这些粒子紧密排列在固定位置，只能振动。在液体中，粒子靠得很近，但可以相互滑动。在气体中，粒子相距很远，并向各个方向快速运动。对于元素，这些粒子是原子；对于化合物，这些粒子是分子或离子。粒子模型有助于解释熔化、沸腾、扩散和压强等现象。
solid ⇌ liquid ⇌ gas (by heating or cooling)
固体 ⇌ 液体 ⇌ 气体（通过加热或冷却）
3. Inside the Atom: Protons, Neutrons, and Electrons | 原子内部：质子、中子和电子
Atoms have a central nucleus, which contains protons and neutrons. Electrons move around the nucleus in shells. Protons carry a positive charge, electrons carry a negative charge, and neutrons have no charge. A neutral atom has equal numbers of protons and electrons, so the positive and negative charges cancel out. The nucleus is tiny compared with the whole atom, but it contains almost all the mass.
原子有一个中心原子核，其中包含质子和中子。电子在电子层中围绕原子核运动。质子带正电荷，电子带负电荷，中子不带电荷。中性原子的质子数和电子数相等，因此正负电荷相互抵消。原子核与整个原子相比极小，但几乎包含了全部质量。
| Subatomic particle 亚原子粒子 | Relative charge 相对电荷 | Location 位置 |
| Proton 质子 | +1 | nucleus 原子核内 |
| Neutron 中子 | 0 | nucleus 原子核内 |
| Electron 电子 | -1 | shells around nucleus 核外电子层 |
4. Atomic Number and Mass Number | 原子序数与质量数
Every atom has an atomic number and a mass number. The atomic number is the number of protons in the nucleus. It tells you which element the atom is. The mass number is the total number of protons plus neutrons. You can write these two numbers beside an element symbol, for example, carbon-12 has 6 protons and 6 neutrons. A neutral atom also has the same number of electrons as protons.
每个原子都有一个原子序数和一个质量数。原子序数是原子核中质子的数目，它告诉你这是哪种元素的原子。质量数是质子数与中子数的总和。你可以把这两个数字写在元素符号旁边，例如碳-12有6个质子和6个中子。中性原子的电子数也与质子数相同。
atomic number = number of protons
原子序数 = 质子数
mass number = number of protons + number of neutrons
质量数 = 质子数 + 中子数
5. Elements and Atoms | 元素与原子
An element is a pure substance made of only one type of atom. For example, oxygen gas contains only oxygen atoms, and a piece of gold contains only gold atoms. There are more than 100 different elements, and each one has its own symbol and atomic number. The periodic table arranges all elements in order of increasing atomic number. Elements in the same group have similar chemical properties because they have the same number of electrons in their outer shell.
元素是由同
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