📚 Atomic Structure: The Building Blocks of Matter | 原子结构：物质的基本单元
Everything around you – from the air you breathe to the screen you are reading on – is made of tiny particles called atoms. Understanding the structure of the atom is essential for explaining why materials behave the way they do, and it forms the foundation of all chemistry and physics.
你周围的一切——从呼吸的空气到正在阅读的屏幕——都由称为原子的微小粒子构成。理解原子结构是解释物质为何具有这些行为的关键，也是所有化学和物理的基础。
1. What Is an Atom? | 什么是原子？
exist and still retain the chemical properties of that element. Atoms are incredibly small – out 0.1 nm (1 × 10⁻¹⁰ m). Each atom consists of a central nucleus surrounded by electrons.
原子是元素保持化学性质的最小微粒。原子非常小——直径约为0.1纳米（1 × 10⁻¹⁰ 米）。每个原子由一个位于中心的原子核以及围绕核运动的电子组成。
The nucleus itself contains protons and neutrons, which are collectively called nucleons. Electrons move in specific energy levels (shells) around the nucleus.
原子核本身包含质子和中子，统称为核子。电子在原子核周围特定的能级（电子壳层）中运动。
2. The Subatomic Particles | 亚原子粒子
There are three main subatomic particles: protons, neutrons and electrons. Each has a specific relative charge and relative mass.
有三种主要的亚原子粒子：质子、中子和电子。每种粒子都有特定的相对电荷和相对质量。
| Particle | Relative Charge | Relative Mass |
| Proton | +1 | 1 |
| Neutron | 0 | 1 |
| Electron | -1 | 1/1840 (negligible) |
Protons and neutrons are found in the nucleus, while electrons occupy the space around it. In a neutral atom, the number of electrons equals the number of protons.
质子和中子位于原子核中，而电子占据核外空间。在中性原子中，电子数目等于质子数目。
3. Atomic Number and Mass Number | 原子序数与质量数
The atomic number (Z) is the number of protons in the nucleus of an atom. It defines which element the atom belongs to. The mass number (A) is the total number of protons and neutrons in the nucleus.
原子序数（Z）是原子核中的质子数。它决定了该原子属于哪种元素。质量数（A）是原子核中质子与中子的总数。
Mass number (A) = Atomic number (Z) + Number of neutrons (N)
For example, a carbon atom with 6 protons and 6 neutrons has atomic number 6 and mass number 12. This is written as ¹²C.
例如，一个具有6个质子和6个中子的碳原子，其原子序数为6，质量数为12，写作¹²C。
4. Isotopes | 同位素
Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. Therefore, they have the same atomic number but different mass numbers.
同位素是同一元素中具有相同质子数但不同中子数的原子。因此，它们具有相同的原子序数但不同的质量数。
- Carbon-12 (¹²C): 6 protons, 6 neutrons
- Carbon-14 (¹⁴C): 6 protons, 8 neutrons
Isotopes have the same chemical properties because chemical behaviour depends on the number and arrangement of electrons, not on the number of neutrons.
同位素具有相同的化学性质，因为化学行为取决于电子的数目和排布，而不是中子数。
Radioactive isotopes such as ¹⁴C are used in carbon dating, while cobalt-60 is used in cancer radiotherapy.
放射性同位素如¹⁴C用于碳定年法，而钴-60用于癌症放射治疗。
5. Electronic Configuration | 电子排布
Electrons occupy energy levels (shells) around the nucleus. The shells are filled from the innermost shell outward. The first shell can hold up to 2 electrons, the second shell up to 8, and the third shell up to 8 as well (for the first 20 elements).
电子在原子核周围的能级（壳层）中排布。电子从最内层壳开始向外填充。第一层最多容纳2个电子，第二层最多容纳8个，第三层对于前20号元素也最多容纳8个。
| Element | Protons | Electron Configuration |
| Hydrogen | 1 | 1 |
| Helium | 2 | 2 |
| Sodium | 11 | 2, 8, 1 |
| Chlorine | 17 | 2, 8, 7 |
The outermost shell is called the valence shell, and the electrons in it are called valence electrons. These electrons are responsible for the atom's chemical reactivity.
最外层被称为价电子层，其中的电子称为价电子。这些电子的数目决定了原子的化学反应活性。
6. Valence Electrons and the Periodic Table | 价电子与元素周期表
Elements in the same group of the periodic table have the same number of valence electrons. For example, all Group 1 elements (lithium, sodium, potassium) have one electron in their outermost shell.
元素周期表中同一族的元素具有相同的价电子数。例如，第1族元素（锂、钠、钾）的最外层都只有1个电子。
This explains why they show similar chemical properties. Noble gases (Group 0) have a full outer shell (2 for helium, 8 for neon and argon), which makes them chemically inert.
这解释了它们为何具有相似的化学性质。稀有气体（第0族）具有满的外层电子（氦为2，氖和氩为8），因此化学性质不活泼。
The period (row) number tells you how many occupied electron shells the element has. For instance, sodium is in period 3 because it has three shells.
周期数（行号）表示该元素占据了多少个电子壳层。例如，钠位于第三周期，因为它有三层电子。
7. Formation of Ions | 离子的形成
Atoms can gain or lose electrons to achieve a stable full outer shell. When an atom loses electrons, it becomes a positively charged ion (cation). When it gains electrons, it becomes a negatively charged ion (anion).
原子可以通过得失电子来获得稳定的满外层结构。当原子失去电子时，变成带正电的离子（阳离子）；当它获得电子时，变成带负电的离子（阴离子）。
Na → Na⁺ + e⁻
Cl + e⁻ → Cl⁻
For example, sodium (2,8,1) loses one electron to form Na⁺ with configuration (2,8). Chlorine (2,8,7) gains one electron to form Cl⁻ with configuration (2,8,8).
例如，钠（2,8,1）失去一个电子形成Na⁺，排布变为（2,8）。氯（2,8,7）获得一个电子形成Cl⁻，排布变为（2,8,8）。
The charge on an ion is written as a superscript after the chemical symbol, e.g., Mg²⁺, O²⁻, Fe³⁺.
离子所带电荷写在化学符号后面作为上标，例如Mg²⁺、O²⁻、Fe³⁺。
8. Calculating Relative Atomic Mass | 计算相对原子质量
Relative atomic mass (Aᵣ) is the weighted average mass of all the isotopes of an element, relative to 1/12 of the mass of a carbon-12 atom. Since isotopes exist in different natural abundances, we must take their percentages into account.
相对原子质量（Aᵣ）是一种元素所有同位素的加权平均质量，相对于碳-12原子质量的1/12。由于不同同位素的自然丰度不同，我们必须考虑它们的百分比。
ge of isotope 1 × mass of isotope 1) + (percentage of isotope 2 × mass of isotope 2) ÷ 100
Example: Chlorine has two isotopes: ³⁵Cl (75%) and ³⁷Cl (25%).
示例：氯有两种同位素：³⁵Cl（占75%）和³⁷Cl（占25%）。
Aᵣ(Cl) = (75 × 35) + (25 × 37) ÷ 100 = (2625 + 925) ÷ 100 = 35.5
This is why the relative atomic mass of chlorine on the periodic table is 35.5, not a whole number.
这就是为什么元素周期表中氯的相对原子质量为35.5，而不是一个整数。
9. The Development of the Atomic Model | 原子模型的发展
The modern understanding of the atom has been built up over centuries. Key scientists include:
现代对原子的理解是经过几个世纪逐步建立的。关键科学家包括：
- John Dalton (1803): Proposed that atoms are solid, indivisible spheres.
- J.J. Thomson (1897): Discovered the electron and proposed the "plum pudding" model – a positive sphere with negative electrons embedded in it.
- Ernest Rutherford (1911): Fired alpha particles at gold foil and discovered that most passed through, but some bounced back. This led to the nuclear model with a tiny, dense, positive nucleus.
- Niels Bohr (1913): Suggested that electrons orbit the nucleus in fixed energy levels.
- James Chadwick (1932): Confirmed the existence of the neutron.
Each step refined the model, showing that science is a process of continual improvement based on evidence.
每一步都对模型进行了完善，表明科学是一个基于证据不断改进的过程。
10. Using Isotopes: Dating and Medicine | 同位素的应用：测年与医学
Radioactive isotopes have many practical uses.
放射性同位素有许多实际用途。
Carbon-14 dating is used to determine the age of ancient organic materials. Living organisms contain a constant ratio of ¹⁴C to ¹²C. When they die, ¹⁴C decays at a known rate, so measuring the remaining ¹⁴C allows scientists to estimate the time of death.
碳-14测年用于确定古代有机材料的年代。活的生物体内含有恒定的¹⁴C与¹²C比例。生物死亡后，¹⁴C以已知速率衰变，因此测量剩余的¹⁴C量可以估算其死亡时间。
Iodine-131 is used in medicine to treat thyroid conditions, as iodine is absorbed by the thyroid gland. Its radiation can destroy harmful cells there.
碘-131在医学上用于治疗甲状腺疾病，因为碘会被甲状腺吸收，其辐射可以杀死有害细胞。
Technetium-99m is used as a tracer in medical imaging; it emits gamma rays that can be detected outside the body.
锝-99m用作医学影像中的示踪剂；它发射伽马射线，可在体外被检测到。
11. Solving Problems with the Atomic Model | 用原子模型解决问题
Using the rules above, you can solve many IGCSE problems. For example:
利用上述规则，你可以解决许多IGCSE考试问题。例如：
An atom X has an atomic number of 13 and a mass number of 27.
原子X的原子序数为13，质量数为27。
- Number of protons = 13
- Number of electrons = 13 (neutral atom)
- Number of neutrons = 27 – 13 = 14
- Electron configuration = 2, 8, 3
It belongs to Group 3 and Period 3. It will lose 3 electrons to form an X³⁺ ion.
它位于第3族、第3周期。它会失去3个电子形成X³⁺离子。
Always check the atomic number and mass number from the periodic table, and remember that the number of electrons equals protons only in neutral atoms.
始终要从周期表中检查原子序数和质量数，并记住只有在中性原子中电子数才等于质子数。
12. Key Takeaways | 核心要点总结
In this revision guide, you have learned:
在本复习指南中，你学到了：
- Atoms are made of protons, neutrons and electrons.
- Protons determine the element's identity.
- Isotopes have the same proton number but different neutron numbers.
- Electronic configurations follow the 2, 8, 8 rule for the first 20 elements.
- Valence electrons control chemical behaviour.
- Ions form by loss or gain of electrons.
- Relative atomic mass is a weighted average of isotope masses.
- The atomic model has developed over time through experiments.
- 原子由质子、中子和电子组成。
- 质子决定元素的种类。
- 同位素具有相同的质子数但不同的中子数。
- 前20号元素的电子排布遵循2、8、8规则。
- 价电子控制化学行为。
- 离子通过得失电子形成。
- 相对原子质量是同位素质量的加权平均值。
- 原子模型通过实验不断演变发展。
Master these ideas, and you will be well prepared for your Edexcel IGCSE Science exam.
掌握这些概念，你就能为Edexcel IGCSE科学考试做好充分准备。
Published by TutorHao | Science Revision Series | aleveler.com
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