📚 Atomic Structure | 原子结构
Understanding atomic structure is the first major step in KS3 chemistry. It explains what everything around us is made of and why different elements behave in different ways.
理解原子结构是 KS3 化学的第一个重要步骤。它解释了我们周围万物的组成以及不同元素为何表现不同。
This revision guide covers the key ideas you need: subatomic particles, the nucleus, electron shells, atomic number, mass number, and common exam mistakes.
本复习指南涵盖你需要掌握的核心概念：亚原子粒子、原子核、电子层、原子序数、质量数以及常见考试误区。
1. What Is an Atom? | 什么是原子？
An atom is the smallest particle of an element that can still be recognised as that element. If you break a piece of pure gold into smaller and smaller pieces, the smallest piece that still behaves like gold is a single gold atom.
原子是元素中仍能保持该元素性质的最小粒子。如果把一块纯金不断分割成越来越小的颗粒，仍然具有金的性质的最小颗粒就是一个金原子。
Atoms can join together to form molecules or giant structures, but a single atom is the basic unit that gives an element its chemical identity.
原子可以结合形成分子或巨型结构，但单个原子是赋予元素化学身份的基本单元。
2. Atoms Are Incredibly Small | 原子极其微小
ght microscope. A typical atom has a radius of about 0.1 nanometres, which is 1 × 10⁻¹⁰ m.
原子小到用肉眼甚至普通光学显微镜都无法看见。一个典型原子的半径约为 0.1 纳米，即 1 × 10⁻¹⁰ 米。
To picture this scale, a single human hair is roughly one million atoms wide. Because atoms are so small, scientists use models to represent them rather than drawings that show their true size.
为了想象这个尺度，一根人的头发大约有一百万个原子那么宽。由于原子如此微小，科学家使用模型来表示它们，而不是按真实大小画图。
Most of an atom is empty space. The nucleus at the centre is about 10,000 times smaller than the atom itself, which means nearly all the volume of an atom contains nothing at all.
原子的大部分是空的。原子中心的原子核大约比原子本身小 10,000 倍，这意味着原子几乎所有的体积都是空的。
3. The Three Subatomic Particles | 三种亚原子粒子
Atoms are made from three types of subatomic particles: protons, neutrons and electrons. Each particle has a different relative charge and relative mass.
原子由三种亚原子粒子组成：质子、中子和电子。每种粒子具有不同的相对电荷和相对质量。
The table below summarises the key facts you need to know for KS3 chemistry.
下表总结了 KS3 化学需要掌握的关键事实。
| Particle (粒子) | Relative charge (相对电荷) | Relative mass (相对质量) | Location (位置) |
|---|---|---|---|
| Proton 质子 | +1 | 1 | Nucleus 原子核 |
| Neutron 中子 | 0 | 1 | Nucleus 原子核 |
| Electron 电子 | −1 | Almost 0 (about 1/1836) 几乎为 0（约 1/1836） | Shells around the nucleus 原子核外的电子层 |
Notice that protons and neutrons have the same relative mass of 1, but an electron has a mass so small that it is usually ignored in KS3 calculations.
注意质子和中子的相对质量都是 1，而电子的质量非常小，在 KS3 计算中通常忽略不计。
4. The Nucleus: Protons and Neutrons | 原子核：质子与中子
The nucleus is the tiny, dense centre of an atom. It contains two types of particles: protons, which carry a positive charge, and neutrons, which have no charge.
原子核是原子中极其微小而致密的中心。它包含两种粒子：带正电的质子和不带电的中子。
Because protons are positive and neutrons are neutral, the nucleus as a whole has a positive charge. Almost all of the mass of an atom is concentrated in its nucleus because protons and neutrons are much heavier than electrons.
由于质子带正电、中子不带电，原子核整体带正电。原子几乎所有的质量都集中在原子核中，因为质子和中子比电子重得多。
Even though the nucleus carries nearly all the mass, it takes up only a tiny fraction of the atom's volume. This is why we say atoms are mostly empty space.
尽管原子核集中了几乎全部质量，但它只占原子体积的极小部分。这就是我们说原子大部分是空的原因。
5. Electrons and Shells | 电子与电子层
Electrons are negatively charged particles that move around the nucleus in regions called shells or energy levels. The shells are arranged at different distances from the nucleus.
电子是带负电的粒子，在被称为电子层或能级的区域中围绕原子核运动。这些电子层与原子核的距离不同。
For the first 20 elements, electron shells fill according to simple rules: the first shell can hold up to 2 electrons, the second shell can hold up to 8 electrons, and the third shell is treated as full with 8 electrons at KS3.
对于前 20 号元素，电子层的填充遵循简单规则：第一层最多容纳 2 个电子，第二层最多容纳 8 个电子，在 KS3 中第三层最多容纳 8 个电子。
The electrons in the outermost shell, called the outer shell, are very important because they determine how an element reacts chemically.
最外层的电子（称为外层电子）非常重要，因为它们决定了元素的化学性质。
6. Atomic Number and Mass Number | 原子序数与质量数
Every element has a unique atomic number, which is the number of protons in the nucleus of one atom of that element. The atomic number tells you which element an atom is.
每种元素都有唯一的原子序数，即该元素一个原子核中的质子数。原子序数告诉你这个原子属于哪种元素。
The mass number is the total number of protons and neutrons in the nucleus. It is always a whole number because you cannot have part of a proton or neutron.
质量数是原子核中质子和中子的总数。它总是整数，因为不可能存在质子和中子的一部分。
mass number = number of protons + number of neutrons
质量数 = 质子数 + 中子数
For example, a carbon atom has 6 protons and usually 6 neutrons, so its mass number is 12. Its atomic number is 6.
例如，一个碳原子有 6 个质子和通常 6 个中子，因此它的质量数是 12，原子序数是 6。
7. Why Atoms Are Neutral | 原子为何呈电中性
In a neutral atom, the number of protons is exactly equal to the number of electrons. The positive charges from the protons cancel out the negative charges from the electrons.
在中性原子中，质子数恰好等于电子数。质子带的正电荷与电子带的负电荷相互抵消。
Because each proton has a charge of +1 and each electron has a charge of −1, an atom with, for example, 8 protons and 8 electrons has an overall charge of zero.
因为每个质子的电荷为 +1，每个电子的电荷为 −1，例如一个有 8 个质子和 8 个电子的原子整体电荷为零。
If an atom gains or loses electrons, it becomes a charged particle called an ion. However, at KS3 you mainly need to understand the neutral atom first.
如果原子得到或失去电子，就会变成带电粒子，称为离子。不过，在 KS3 阶段你首先需要理解中性原子。
8. Electron Arrangement for the First 20 Elements | 前20号元素的电子排布
Chemists often write electron arrangements as a series of numbers separated by commas. Each number shows how many electrons are in a particular shell.
化学家通常用逗号分隔的一串数字来表示电子排布。每个数字表示某一电子层中的电子数量。
The table below shows the electron arrangements for the first 20 elements. Notice how the pattern changes as the atomic number increases.
下表显示了前 20 号元素的电子排布。注意随着原子序数增加，排布模式如何变化。
| Element (元素) | Symbol (符号) | Atomic number (原子序数) | Electron arrangement (电子排布) |
|---|---|---|---|
| Hydrogen 氢 | H | 1 | 1 |
| Helium 氦 | He | 2 | 2 |
| Lithium 锂 | Li | 3 | 2,1 |
| Beryllium 铍 | Be | 4 | 2,2 |
| Boron 硼 | B | 5 | 2,3 |
| Carbon 碳 | C | 6 | 2,4 |
| Nitrogen 氮 | N | 7 | 2,5 |
| Oxygen 氧 | O | 8 | 2,6 |
| Fluorine 氟 | F | 9 | 2,7 |
| Neon 氖 | Ne | 10 | 2,8 |
| Sodium 钠 | Na | 11 | 2,8,1 |
| Magnesium 镁 | Mg | 12 | 2,8,2 |
| Aluminium 铝 | Al | 13 | 2,8,3 |
| Silicon 硅 | Si | 14 | 2,8,4 |
| Phosphorus 磷 | P | 15 | 2,8,5 |
| S
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