Atomic Structure and the Periodic Table | 原子结构与元素周期表

📚 Atomic Structure and the Periodic Table | 原子结构与元素周期表

This revision guide covers the core ideas of atomic structure and the periodic table for the Edexcel IGCSE Science syllabus. You will learn how atoms are built, how the periodic table is organised, and how the position of an element relates to its properties.

本复习指南涵盖 Edexcel IGCSE 科学大纲中原子结构与元素周期表的核心概念。你将了解原子如何构成、元素周期表如何排列，以及元素的位置如何与其性质相关联。

1. The Structure of an Atom | 原子的结构

Every atom is made of three subatomic particles: protons, neutrons and electrons. Protons and neutrons are packed together in the tiny nucleus at the centre, while electrons move around the nucleus in shells.

每个原子都由三种亚原子粒子构成：质子、中子和电子。质子和中子紧密聚集在中心的微小原子核中，而电子在核外的电子壳层中运动。

Proton: positive charge, relative mass 1, found in the nucleus.
Neutron: no charge, relative mass 1, found in the nucleus.
Electron: negative charge, relative mass 1/1840, found in shells.

质子：带正电，相对质量为 1，位于原子核中。
中子：不带电，相对质量为 1，位于原子核中。
电子：带负电，相对质量约为 1/1840，位于电子壳层中。

Atomic number = number of protons
Mass number = number of protons + number of neutrons

原子序数 = 质子数
质量数 = 质子数 + 中子数

In a neutral atom, the number of electrons equals the number of protons, so the overall charge is zero.

在中性原子中，电子数等于质子数，因此总电荷为零。

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

The atomic number (Z) identifies the element. The mass number (A) tells you the total number of protons and neutrons in the nucleus.

原子序数（Z）决定了元素的种类。质量数（A）表示原子核中质子与中子的总数。

For example, a sodium atom has atomic number 11 and mass number 23. This means it has 11 protons, 11 electrons and 23 − 11 = 12 neutrons.

例如，一个钠原子原子序数为 11，质量数为 23。这意味着它有 11 个质子、11 个电子和 23 − 11 = 12 个中子。

Symbol representation	Example: ²³₁₁Na
Meaning	Mass number is 23, atomic number is 11

Number of neutrons = mass number − atomic number

中子数 = 质量数 − 原子序数

3. Isotopes | 同位素

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

同位素是同一元素的原子，具有相同的质子数但不同的中子数。因此它们具有相同的原子序数但不同的质量数。

For example, carbon-12 (¹²C) and carbon-14 (¹⁴C) are both carbon atoms, but carbon-14 has two extra neutrons.

例如，碳-12（¹²C）和碳-14（¹⁴C）都是碳原子，但碳-14 多了两个中子。

Isotopes have the same chemical properties because they have the same number of electrons.
Isotopes may have different physical properties, such as density or rate of diffusion.

同位素具有相同的化学性质，因为它们具有相同的电子数。
同位素可能具有不同的物理性质，例如密度或扩散速率。

4. Electron Shells and Electronic Configuration | 电子壳层与电子排布

Electrons occupy shells (energy levels) around the nucleus. The first shell can hold up to 2 electrons, the second and third shells can hold up to 8 electrons each.

电子占据原子核周围的壳层（能级）。第一层最多容纳 2 个电子，第二层和第三层最多各容纳 8 个电子。

Electronic configuration shows how the electrons are arranged in the shells. For example, sodium has 11 electrons, so its configuration is 2.8.1.

电子排布表示电子在壳层中的分布方式。例如，钠有 11 个电子，因此其排布为 2.8.1。

Electron shells fill from the innermost shell outwards.

电子壳层从最内层开始向外填充。

The number of electrons in the outermost shell determines how an element reacts chemically.

最外层电子数决定了元素的化学反应方式。

5. The Periodic Table: Groups and Periods | 元素周期表：族与周期

The periodic table arranges elements in order of increasing atomic number. A row is called a period, and a column is called a group.

元素周期表按照原子序数递增的顺序排列元素。横行为周期，纵列为族。

Group number = number of outer-shell electrons (for Groups 1–2 and 13–18).
Period number = number of occupied electron shells.

族号 = 最外层电子数（适用于第 1–2 族和第 13–18 族）。
周期号 = 电子所占的壳层数。

For example, chlorine is in Group 7 and Period 3. It has 7 outer-shell electrons and 3 shells.

例如，氯位于第 7 族、第 3 周期。它有 7 个最外层电子和 3 个电子壳层。

6. Group 1: Alkali Metals | 第 1 族：碱金属

Group 1 elements, such as lithium, sodium and potassium, are soft metals that react vigorously with water.

第 1 族元素，如锂、钠和钾，是柔软的金属，能与水剧烈反应。

They have one outer-shell electron.
They are very reactive and become more reactive down the group.
They form compounds with a charge of +1.

它们只有一个最外层电子。
它们非常活泼，且越往下越活泼。
它们形成 +1 价的化合物。

Down the group, atoms get larger, the outer electron is further from the nucleus and is easier to lose, so reactivity increases.

同族往下，原子变大，外层电子离核更远，更容易失去，因此反应活性增强。

7. Group 7: Halogens | 第 7 族：卤素

Group 7 elements, such as fluorine, chlorine, bromine and iodine, are non-metals with reactive diatomic molecules.

第 7 族元素，如氟、氯、溴和碘，是非金属，能形成活泼的双原子分子。

They have seven outer-shell electrons.
They typically gain one electron to form a −1 ion.
Reactivity decreases down the group.

它们有 7 个最外层电子。
它们通常获得一个电子，形成 −1 价离子。
同族往下，反应活性减弱。

A more reactive halogen can displace a less reactive halogen from its salt solution. For example, chlorine displaces bromine from potassium bromide solution.

较活泼的卤素可以从其盐溶液中置换出较不活泼的卤素。例如，氯能从溴化钾溶液中置换出溴。

Cl₂ + 2KBr → 2KCl + Br₂

8. Group 0: Noble Gases | 第 0 族：稀有气体

Group 0 elements, including helium, neon and argon, are monatomic and very unreactive because their outer shells are full.

第 0 族元素，包括氦、氖和氩，是单原子气体，由于最外层电子已经排满，因此非常不活泼。

Helium has 2 outer-shell electrons; neon and argon have 8.
They exist as single atoms, not molecules.
They have high ionisation energies and no tendency to lose or gain electrons.

氦有 2 个最外层电子；氖和氩有 8 个。
它们以单原子形式存在，而不是分子。
它们具有很高的电离能，没有失去或获得电子的趋势。

The full outer shell gives them a stable electronic configuration, which is why they are often called ‘noble’ or ‘inert’ gases.

充满的最外层使它们具有稳定的电子排布，因此常被称为“惰性气体”。

9. Metals and Non-Metals | 金属与非金属

The periodic table can be divided into metals on the left and non-metals on the right, separated by a staircase line.

元素周期表可以划分为左侧的金属和右侧的非金属，两者之间以阶梯线分界。

Property	Metal	Non-metal
Conductivity	Good conductor of heat and electricity	Poor conductor (except graphite)
Malleability	Malleable and ductile	Brittle when solid
Oxide	Basic oxide	Acidic oxide

性质	金属	非金属
导电性	良好导电导热	较差（石墨除外）
延展性	可延展、可锻造	固态时脆
氧化物	碱性氧化物	酸性氧化物

10. Trends in the Periodic Table | 元素周期表中的递变规律

Several properties show clear trends across a period and down a group.

许多性质在周期和族中表现出明显的递变规律。

Across a period: number of outer-shell electrons increases; atomic radius decreases; nuclear charge increases.
Down a group: number of shells increases; atomic radius increases; shielding increases.

同一周期从左到右：最外层电子数增加；原子半径减小；核电荷数增加。
同一族从上到下：电子壳层数增加；原子半径增大；屏蔽效应增强。

These trends explain why elements at the left of a period are more metallic, while those at the right are more non-metallic.

这些规律解释了为什么周期左侧的元素金属性更强，而右侧的元素非金属性更强。

11. Ion Formation and Noble Gas Configuration | 离子形成与稀有气体电子构型

Atoms lose or gain electrons to achieve the stable electron configuration of a noble gas. This forms ions.

原子通过失去或获得电子来达到稀有气体的稳定电子构型，从而形成离子。

Metals tend to lose electrons to form positive ions (cations). Non-metals tend to gain electrons to form negative ions (anions).

金属倾向于失去电子形成正离子（阳离子）。非金属倾向于获得电子形成负离子（阴离子）。

Na → Na⁺ + e⁻
Cl + e⁻ → Cl⁻

The charge of an ion is determined by how many electrons are lost or gained to reach a full outer shell.

离子所带电荷取决于为了达到充满的最外层而失去或获得的电子数。

12. Exam Tips and Common Mistakes | 考试技巧与常见错误

Here are some quick points to remember in the exam.

以下是一些考试中需要注意的要点。

Always write the number of protons before neutrons when calculating mass number.
Do not confuse atomic number with mass number. In ²³₁₁Na, the top number is mass number.
Remember that isotopes have the same electronic configuration, so they react the same way.

计算质量数时，始终先确定质子数再确定中子数。
不要混淆原子序数与质量数。在 ²³₁₁Na 中，上方数字是质量数。
记住同位素具有相同的电子排布，因此它们具有相同的化学反应方式。

When drawing electronic configurations, fill the inner shells first and never put more than 2 electrons in the first shell or 8 in the second and third shells.

画电子排布时，先填满内层，第一层不能超过 2 个电子，第二层和第三层不能超过 8 个电子。

Always state the ‘full outer shell’ reason when explaining why noble gases are unreactive or why ions form.

解释稀有气体不活泼或离子形成原因时，一定要提到“最外层为全满”这一要点。

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Atomic Structure and the Periodic Table | 原子结构与元素周期表