The Structure of the Atom | 原子结构

📚 The Structure of the Atom | 原子结构

In this revision article, we explore the fundamental model of the atom, the tiny building block of all matter. You will learn about the three subatomic particles, how to determine atomic and mass numbers, and why isotopes behave so similarly in chemical reactions. This topic is essential for your IGCSE Edexcel Science examination.

在这篇复习文章中，我们探讨原子的基本模型——构成所有物质的微小单元。你将了解三种亚原子粒子、如何确定原子序数与质量数，以及为什么同位素在化学反应中具有相似的化学性质。这一主题对 IGCSE Edexcel 科学考试至关重要。

1. The Historical Journey | 历史的探索之路

The idea of the atom has evolved over centuries. John Dalton proposed that atoms were solid, indivisible spheres. J.J. Thomson later discovered the electron and suggested a ‘plum pudding’ model, where negatively charged electrons were embedded in a positive cloud.

原子的概念经过数百年演进。道尔顿提出原子是实心、不可分割的球体。后来汤姆森发现了电子，并提出了“葡萄干布丁”模型：带负电的电子镶嵌在带正电的弥散云雾中。

Ernest Rutherford’s gold foil experiment in 1911 changed this view. He fired alpha particles at thin gold foil and found most passed through, but a few bounced back. This led to the nuclear model: a tiny, dense, positively charged nucleus surrounded by mostly empty space.

1911 年，卢瑟福的金箔实验改变了这一观点。他用α粒子轰击极薄的金箔，发现大多数粒子穿过，但少数反弹回来。由此提出了核模型：一个微小、致密、带正电的原子核，周围大部分是空的空间。

2. Subatomic Particles | 亚原子粒子

The modern atom contains three key particles: protons, neutrons and electrons. Protons and neutrons are found in the nucleus, while electrons occupy shells outside it.

现代原子包含三种关键粒子：质子、中子和电子。质子和中子位于原子核内，而电子则在核外的电子壳层中运动。

Protons carry a positive charge, electrons carry a negative charge, and neutrons have no charge. Because protons and electrons have equal but opposite charges, the atom is electrically neutral.

质子带正电，电子带负电，中子不带电。由于质子与电子所带电荷量相等且相反，因此原子整体呈电中性。

The mass of protons and neutrons is approximately 1 atomic mass unit (amu), while electrons are about 1/1836 of that mass. This makes the nucleus almost the entire mass of the atom.

质子与中子的质量约为 1 个原子质量单位（amu），而电子的质量约为其 1/1836。因此，原子核几乎集中了原子的全部质量。

3. Properties Table | 性质一览表

Particle	Charge	Mass (amu)	Location
Proton	+1	1	Nucleus
Neutron	0	1	Nucleus
Electron	−1	~1/1836	Electron shells

You must memorise the charge and relative mass of each particle. The electron’s mass is often taken as 0 in calculations because it is so small.

你必须牢记每种粒子的电荷和相对质量。由于电子的质量极小，在计算中通常近似为 0。

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

The atomic number (Z) is the number of protons in an atom. It defines the element. For example, any atom with 6 protons is carbon.

原子序数（Z）是原子中的质子数，它定义了元素的种类。例如，任何含有 6 个质子的原子都是碳。

The mass number (A) is the total number of protons and neutrons in the nucleus. The number of neutrons can be found by subtracting the atomic number from the mass number.

质量数（A）是原子核中质子与中子的总数。要计算中子数，只需用质量数减去原子序数。

Neutron number = Mass number − Atomic number

中子数 = 质量数 − 原子序数

In element notation, the mass number is placed as a superscript before the symbol, and the atomic number as a subscript. For example, carbon-12 is written as ¹²₆C.

在元素符号中，质量数以正上标形式写在符号左侧，原子序数以正下标形式写在下方。例如，碳-12 写作 ¹²₆C。

5. Isotopes | 同位素

Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. Thus they have the same atomic number but different mass numbers.

同位素是同一元素的不同原子，它们质子数相同，但中子数不同。因此，它们的原子序数相同，质量数不同。

For example, chlorine has two common isotopes: chlorine-35 (¹⁷₁₇Cl? Actually ³⁵₁₇Cl) and chlorine-37 (³⁷₁₇Cl). Both have 17 protons, but one has 18 neutrons and the other has 20.

例如，氯有两种常见同位素：氯-35（³⁵₁₇Cl）和氯-37（³⁷₁₇Cl）。两者都有 17 个质子，但一个含 18 个中子，另一个含 20 个中子。

Isotopes of the same element show identical chemical properties because chemical behaviour depends on the number and arrangement of electrons, not on the neutron number.

同一元素的同位素具有完全相同的化学性质，因为化学行为取决于电子数目及排列，而非中子数。

However, physical properties such as mass and density can differ. Radioactive isotopes are widely used in medicine, archaeology and industry.

然而，物理性质如质量和密度可能不同。放射性同位素广泛应用于医学、考古和工业领域。

6. Electron Shell Configuration | 电子壳层排布

Electrons are arranged in energy levels called shells. The first shell can hold a maximum of 2 electrons, and the second and third shells can hold up to 8 electrons each.

电子分布在称为壳层的能级中。第一层最多容纳 2 个电子，第二层和第三层最多可各容纳 8 个电子。

Electrons fill the innermost shell first. When it is full, they occupy the next shell. This arrangement is called the electronic configuration or electronic structure.

电子首先填充最内层。当第一层填满后，再进入下一层。这种排布称为电子排布式或电子结构。

For example, an atom of sodium (Na) has 11 electrons. Its configuration is 2,8,1. This tells us that sodium has two electrons in the first shell, eight in the second, and one in the outer shell.

例如，钠（Na）原子有 11 个电子。其排布为 2,8,1。这意味着钠在第一层有 2 个电子，第二层有 8 个，最外层有 1 个。

Maximum electrons in a shell = 2n², where n is the shell number

每个壳层最大电子数 = 2n²，其中 n 为壳层序数

The outermost shell is called the valence shell. It is responsible for how an atom reacts. Elements with a full outer shell are stable, like the noble gases.

最外层称为价电子层，它决定原子如何发生反应。具有满外层电子的元素非常稳定，如稀有气体。

7. The Periodic Table and the Atom | 元素周期表与原子

The periodic table is arranged according to atomic number. The number of protons increases by one as you move left to right across a period.

元素周期表按原子序数递增排列。从左到右跨越一个周期时，质子数逐个增加。

The group number for main-group elements tells you the number of electrons in the outer shell. For example, Group 1 elements have one outer electron, while Group 7 elements have seven outer electrons.

对于主族元素，其族数表示最外层电子数。例如，第 1 族元素最外层有 1 个电子，第 7 族元素最外层有 7 个电子。

The period number indicates the number of occupied electron shells. Sodium (Na) is in Period 3 because it has three electron shells: 2,8,1.

周期数表示占据的电子壳层数。钠（Na）位于第三周期，因为它有三个电子壳层：2,8,1。

Element	Atomic number	Electron arrangement	Group / Period
Fluorine (F)	9	2,7	Group 7, Period 2
Magnesium (Mg)	12	2,8,2	Group 2, Period 3

This relationship helps you predict the electronic structure of any main-group element simply from its position on the table.

这一关系帮助你仅根据主族元素在周期表中的位置预测其电子结构。

8. Ions and Ionisation | 离子与电离

Atoms gain or lose electrons to form ions. This process is called ionisation. A metal atom tends to lose its outer electrons, becoming a positively charged cation.

原子通过获得或失去电子形成离子，这一过程称为电离。金属原子倾向于失去外层电子，成为带正电的阳离子。

A non-metal atom usually gains electrons to complete its outer shell, forming a negatively charged anion.

非金属原子通常获得电子以填满最外层，形成带负电的阴离子。

For example, a sodium atom (2,8,1) loses its outer electron to become Na⁺ with configuration 2,8. A chlorine atom (2,8,7) gains one electron to become Cl⁻ with configuration 2,8,8.

例如，钠原子（2,8,1）失去最外层一个电子后变成 Na⁺，排布为 2,8。氯原子（2,8,7）获得一个电子后变成 Cl⁻，排布为 2,8,8。

Na → Na⁺ + e⁻

Cl + e⁻ → Cl⁻

The number of charges on an ion equals the number of electrons gained or lost. The periodic table group number can help you predict the charge: Group 1 forms +1, Group 2 forms +2, Group 6 forms −2, and Group 7 forms −1.

离子所带电荷数等于获得或失去的电子数。周期表中的族数可帮助预测电荷：第 1 族形成 +1，第 2 族形成 +2，第 6 族形成 −2，第 7 族形成 −1。

9. Relative Atomic Mass | 相对原子质量

The relative atomic mass (Aᵣ) of an element is the weighted average mass of its isotopes compared with 1/12 of the mass of a carbon-12 atom. It has no units.

元素的相对原子质量（Aᵣ）是其同位素的加权平均质量与碳-12 原子质量的 1/12 之比。它没有单位。

To calculate Aᵣ from isotopic abundances, use the following formula:

要由同位素丰度计算 Aᵣ，请使用以下公式：

Aᵣ = (mass of isotope 1 × abundance of isotope 1 + mass of isotope 2 × abundance of isotope 2) / total abundance

Aᵣ =（同位素 1 的质量 × 同位素 1 的丰度 + 同位素 2 的质量 × 同位素 2 的丰度）÷ 总丰度

For example, chlorine consists of 75% ³⁵Cl and 25% ³⁷Cl. Its relative atomic mass is:

例如，氯由 75% 的 ³⁵Cl 和 25% 的 ³⁷Cl 组成。其相对原子质量为：

(35 × 75 + 37 × 25) / 100 = (2625 + 925) / 100 = 35.5

（35 × 75 + 37 × 25）÷ 100 =（2625 + 925）÷ 100 = 35.5

This explains why chlorine’s relative atomic mass is not a whole number.

这就解释了为什么氯的相对原子质量不是整数。

10. Applications and Exam Tips | 应用与考试提示

Radioactive isotopes like carbon-14 are used for carbon dating of ancient materials. Cobalt-60 is used in cancer radiotherapy, and iodine-131 helps diagnose thyroid disorders.

放射性同位素如碳-14 用于古物的碳定年。钴-60 用于癌症放射治疗，碘-131 用于诊断甲状腺疾病。

In industry, isotopes can be used to check for leaks in pipelines or to measure the thickness of materials.

在工业中，同位素可用于检测管道泄漏或测量材料厚度。

For your exam, remember the following key points:

为了应考，请记住以下要点：

Protons determine the identity of an element.
质子决定元素的种类。
Isotopes have identical chemical properties.
同位素具有完全相同的化学性质。
Electron configuration controls chemical reactivity.
电子排布控制化学活性。
Aᵣ is a weighted average, not a simple mean.
Aᵣ 是加权平均值，不是简单平均数。

Practise drawing electron configurations and calculating relative atomic masses. These skills are frequently tested in structured questions.

练习画出电子排布并计算相对原子质量。这些技能在结构化问答题中经常出现。

11. Summary | 总结

The atom consists of a central nucleus containing protons and neutrons, surrounded by electrons in shells. The atomic number equals the number of protons, while the mass number is the sum of protons and neutrons.

原子由一个包含质子和中子的中心原子核以及核外电子壳层组成。原子序数等于质子数，质量数是质子与中子之和。

Isotopes are atoms with the same number of protons but different numbers of neutrons. Their chemical behaviour is identical because it depends on electron arrangement.

同位素是质子数相同但中子数不同的原子。由于化学行为取决于电子排布，所以同位素的化学性质完全相同。

Mastering the structure of the atom forms the foundation for understanding chemical bonding, reactions and the periodic table. Use this guide to reinforce your revision and build confidence for the IGCSE Edexcel Science examination.

掌握原子结构是理解化学键、化学反应和元素周期表的基础。请使用本指南巩固复习，为 IGCSE Edexcel 科学考试建立信心。

Published by TutorHao | Science Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）

The Structure of the Atom | 原子结构