The Structure of the Atom | 原子结构

📚 The Structure of the Atom | 原子结构

The atom is the fundamental building block of all matter. Understanding its internal structure is essential for explaining chemical reactions, radioactivity, and the organisation of the periodic table. In this revision article, we will explore the key ideas from the Edexcel IGCSE Science specification, focusing on protons, neutrons, electrons, isotopes, electronic configurations, and relative atomic mass.

原子是构成所有物质的基本微粒。理解原子的内部结构，对于解释化学反应、放射现象以及元素周期表的排列方式至关重要。在这篇复习文章中，我们将围绕 Edexcel IGCSE 科学大纲中的核心内容，重点学习质子、中子、电子、同位素、电子排布和相对原子质量等概念。

1. Atoms and Elements | 原子与元素

An atom is the smallest particle of a chemical element that can exist and still retain the chemical properties of that element. Elements are pure substances made from only one kind of atom. For example, oxygen is made only of oxygen atoms, and gold is made only of gold atoms.

原子是化学元素能够存在的最小微粒，并且仍然保持着该元素的化学性质。元素是由同一种原子组成的纯净物。例如，氧气只由氧原子组成，黄金只由金原子组成。

Atoms are extremely small. A single atom is typically about 0.1 nanometres in diameter. Because of their tiny size, scientists use models to help us picture how atoms are arranged. The modern model describes a central nucleus surrounded by orbiting electrons.

原子极其微小。一个原子直径通常约为 0.1 纳米。由于尺寸太小，科学家们使用模型来帮助我们想象原子的排布方式。现代模型描述了一个位于中心、带正电的原子核，以及核外围绕运动的电子。

An element cannot be broken down into simpler substances by chemical reactions. Each element is represented by a chemical symbol, such as H for hydrogen, C for carbon, and Na for sodium. The periodic table arranges all known elements in order of their atomic number.

元素不能通过化学反应分解成更简单的物质。每种元素都有一个化学符号，例如 H 表示氢，C 表示碳，Na 表示钠。元素周期表按原子序数的顺序排列所有已知元素。

2. Subatomic Particles | 亚原子粒子

Every atom contains three main types of subatomic particles: protons, neutrons, and electrons. Protons have a positive charge, electrons have a negative charge, and neutrons have no charge. Together, protons and neutrons are located in the tiny nucleus at the centre of the atom, while electrons move around the nucleus in energy levels.

每个原子都包含三种主要的亚原子粒子：质子、中子和电子。质子带正电荷，电子带负电荷，中子不带电荷。质子和中子位于原子中心极小的原子核内，而电子则在核外的能量层中运动。

The relative masses and charges of these particles are shown in the table below. Note that the mass of an electron is so small that it is often taken as nearly zero.

下表列出了这些粒子的相对质量和电荷。注意，电子的质量非常小，通常近似为零。

Particle	Relative charge	Relative mass
Proton	+1	1
Neutron	0	1
Electron	-1	1/1836 (approx. 0)

In a neutral atom, the number of protons is equal to the number of electrons. This means the positive and negative charges balance exactly, so the atom has no overall charge.

在一个中性原子中，质子数等于电子数。这意味着正电荷和负电荷恰好平衡，因此原子整体上不显电性。

3. Atomic Number and Mass Number | 原子序数与质量数

The atomic number (often given the symbol Z) is the number of protons in the nucleus of an atom. It defines which element the atom belongs to. For example, every carbon atom has atomic number 6, so carbon contains 6 protons.

原子序数（通常用符号 Z 表示）是原子核中的质子数。它决定了原子属于哪一种元素。例如，每个碳原子的原子序数都是 6，因此碳含有 6 个质子。

The mass number (also called nucleon number, symbol A) is the total number of protons and neutrons in the nucleus. Since electrons have negligible mass, the mass number is effectively the number of particles in the nucleus.

质量数（也称核子数，符号 A）是原子核中质子数和中子数的总和。由于电子质量可忽略不计，质量数实际上就是原子核中粒子的总数。

We can calculate the number of neutrons by subtracting the atomic number from the mass number:

我们可以通过质量数减去原子序数来计算中子数：

number of neutrons = mass number – atomic number

中子数 = 质量数 – 原子序数

For example, an atom with a mass number of 23 and an atomic number of 11 has 12 neutrons. This atom is sodium-23.

例如，一个质量数为 23、原子序数为 11 的原子有 12 个中子。这个原子是钠-23。

4. Isotopes | 同位素

Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. Because the proton number is the same, isotopes are the same element and behave similarly in chemical reactions.

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。由于质子数相同，它们属于同一种元素，并且在化学反应中表现相似。

For example, carbon-12 and carbon-14 are both isotopes of carbon. A carbon-12 nucleus has 6 protons and 6 neutrons, while a carbon-14 nucleus has 6 protons and 8 neutrons. The difference in neutron number affects the mass number but not the chemical identity.

例如，碳-12 和碳-14 都是碳的同位素。碳-12 原子核有 6 个质子和 6 个中子，而碳-14 原子核有 6 个质子和 8 个中子。中子数的差异影响了质量数，但不会改变其化学性质。

Isotopes may be stable or unstable. Unstable isotopes are radioactive, meaning they decay over time and emit radiation. This property is used in medicine for imaging and cancer treatment, and in archaeology for carbon dating.

同位素可能是稳定的，也可能是不稳定的。不稳定的同位素具有放射性，这意味着它们会随时间衰变并释放辐射。这一特性被用于医学成像和癌症治疗，以及考古学中的碳定年法。

5. Electronic Configuration | 电子排布

Electrons are arranged in shells around the nucleus. Each shell can hold a maximum number of electrons: the first shell can hold up to 2, the second and third shells can hold up to 8 electrons each. This pattern is often written as a series of numbers, for example 2,8,1 for sodium.

电子围绕原子核分层排布。每一层能够容纳的电子数有限：第一层最多容纳 2 个，第二层和第三层最多各容纳 8 个。这种排布通常用数字序列表示，例如钠的 2,8,1。

We write the electronic configuration by filling the shells from the innermost to the outermost. For carbon (atomic number 6), the configuration is 2,4. For oxygen (atomic number 8), it is 2,6. For argon (atomic number 18), it is 2,8,8.

我们按照从内层到外层的顺序来书写电子排布。对于碳（原子序数 6），电子排布是 2,4；对于氧（原子序数 8），是 2,6；对于氩（原子序数 18），是 2,8,8。

The electrons in the outermost shell are called valence electrons. They are responsible for the chemical behaviour of the atom. Atoms tend to lose, gain, or share electrons so that they achieve a stable full outer shell, usually with 8 electrons.

最外层电子称为价电子。它们决定了原子的化学行为。原子倾向于失去、获得或共享电子，以使最外层达到稳定的满壳层结构，通常是 8 个电子。

6. Relative Atomic Mass | 相对原子质量

Since atoms are incredibly small, their actual masses are not convenient to use in calculations. Instead, chemists use relative atomic mass (Aᵣ). This compares the mass of one atom to 1/12 of the mass of a carbon-12 atom.

由于原子极其微小，实际质量在计算中很不方便。因此，化学家们使用相对原子质量（Aᵣ）。它是以碳-12 原子质量的 1/12 为标准进行比较而得出的数值。

Relative atomic mass has no units because it is a ratio. For a pure element, Aᵣ is often written as an average value taking into account the natural abundance of isotopes.

相对原子质量是一个比值，因此没有单位。对于一种元素，Aᵣ 通常是考虑其同位素天然丰度后的平均值。

To calculate the average atomic mass of an element with two isotopes, we use the following formula:

要计算含有两种同位素的元素的平均原子质量，我们使用以下公式：

Aᵣ = (isotope mass × abundance₁ + isotope mass₂ × abundance₂) / 100

相对原子质量 = (同位素质量 × 丰度₁ + 同位素质量₂ × 丰度₂) / 100

For example, chlorine has two stable isotopes: chlorine-35 (75%) and chlorine-37 (25%). Its average relative atomic mass is (35 × 75 + 37 × 25)/100 = 35.5. This is why the relative atomic mass of chlorine in the periodic table is written as 35.5.

例如，氯有两种稳定同位素：氯-35（占 75%）和氯-37（占 25%）。其平均相对原子质量为 (35 × 75 + 37 × 25)/100 = 35.5。这就是为什么氯在周期表中的相对原子质量写作 35.5。

7. Ions and Electron Transfer | 离子与电子转移

Atoms can become charged by losing or gaining electrons. A neutral atom has equal numbers of protons and electrons. If an atom loses one or more electrons, it has more protons than electrons and becomes a positive ion. If it gains electrons, it becomes a negative ion.

原子可以通过失去或获得电子而带电。中性原子的质子数和电子数相等。如果原子失去一个或多个电子，质子数就会多于电子数，从而成为正离子。如果获得电子，则成为负离子。

Metals tend to lose electrons, forming positive ions. For example, a sodium atom loses one electron to become a sodium ion, Na⁺. A magnesium atom loses two electrons to become Mg²⁺. Non-metals tend to gain electrons, forming negative ions. For example, a chlorine atom gains one electron to become Cl⁻.

金属倾向于失去电子，形成正离子。例如，钠原子失去一个电子成为钠离子 Na⁺；镁原子失去两个电子成为 Mg²⁺。非金属倾向于获得电子，形成负离子。例如，氯原子获得一个电子成为 Cl⁻。

The charge on an ion shows how many electrons have been gained or lost. Ions with opposite charges attract each other through ionic bonds, which are strong forces that hold ionic compounds together.

离子所带的电荷显示了其获得或失去电子的数量。带相反电荷的离子通过离子键相互吸引，这种强作用力将离子化合物牢固地结合在一起。

8. The Periodic Table and Atomic Structure | 元素周期表与原子结构

The periodic table is arranged in columns called groups and rows called periods. The position of an element is directly linked to its atomic structure.

元素周期表按列（称为族）和行（称为周期）排列。元素的位置与其原子结构直接相关。

The group number of a main-group element equals the number of electrons in its outermost shell. For example, all elements in Group 1 have 1 valence electron. Lithium (2,1), sodium (2,8,1), and potassium (2,8,8,1) all have one outer electron. This gives them similar chemical properties.

主族元素的族序数等于其最外层电子数。例如，第 1 族的所有元素都有 1 个价电子。锂（2,1）、钠（2,8,1）和钾（2,8,8,1）都只有一个外层电子，因此它们具有相似的化学性质。

The period number equals the number of electron shells an atom has. Elements in Period 2 have two shells, such as carbon (2,4) and oxygen (2,6). Elements in Period 3 have three shells, such as aluminium (2,8,3) and chlorine (2,8,7).

周期数等于原子的电子壳层数。第 2 周期的元素有两个壳层，例如碳（2,4）和氧（2,6）。第 3 周期的元素有三个壳层，例如铝（2,8,3）和氯（2,8,7）。

As you move across a period, the atomic number increases and the electron shells fill gradually. As you move down a group, the atoms have more shells, so the atomic radius increases and the outer electrons are further from the nucleus.

当沿着周期从左向右移动时，原子序数增加，电子壳层逐渐填满。当沿着族从上向下移动时，原子具有更多壳层，因此原子半径增大，外层电子距原子核更远。

9. Summary and Key Exam Tips | 总结与考试要点

In this article, we have reviewed the structure of the atom, including the properties and locations of protons, neutrons, and electrons. We also discussed atomic number, mass number, isotopes, electronic configurations, relative atomic mass, and the formation of ions.

在这篇文章中，我们复习了原子的结构，包括质子、中子和电子的性质与位置。我们还讨论了原子序数、质量数、同位素、电子排布、相对原子质量和离子的形成。

For exams, remember the following key points:

考试时需要记住以下关键点：

The atomic number is the number of protons. In a neutral atom, this equals the number of electrons.

原子序数就是质子数。在中性原子中，它等于电子数。
Mass number = protons + neutrons. Neutrons do not affect chemical properties.

质量数 = 质子数 + 中子数。中子不影响化学性质。
Isotopes have the same proton number but different neutron numbers.

同位素具有相同的质子数，但中子数不同。
Electronic configuration shows how electrons are arranged in shells. The group number relates to the outer-shell electrons, and the period number relates to the number of shells.

电子排布显示了电子在壳层中的分布。族序数与最外层电子数相关，周期数与壳层数相关。
When calculating relative atomic mass, use the weighted average of isotope masses based on their abundances.

计算相对原子质量时，要根据同位素的丰度求加权平均值。

Be careful with ionic charges and the notation of ions. For example, sodium loses one electron to form Na⁺, while magnesium loses two to form Mg²⁺. Always check the number of electrons gained or lost.

注意离子电荷和离子符号的书写。例如，钠失去一个电子形成 Na⁺，而镁失去两个电子形成 Mg²⁺。始终检查得失电子的数量。

Practise drawing electronic diagrams and writing configurations for common elements. This will help you save time in the exam and avoid simple mistakes. Good luck with your revision!

多练习绘制电子结构示意图并书写常见元素的电子排布，这将帮助你在考试中节省时间并避免低级错误。祝复习顺利！

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The Structure of the Atom | 原子结构