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

Understanding the atom is the foundation of all chemistry and physics. In this revision article, we will explore how atoms are built, how their particles are arranged, and how the periodic table organises elements by atomic structure. This is a core topic for Edexcel IGCSE Science.

理解原子是所有化学和物理的基础。在这篇复习文章中，我们将探索原子如何构成、其粒子如何排列，以及元素周期表如何根据原子结构组织元素。这是 Edexcel IGCSE 科学的核心主题。

1. The Atom and Its Discovery | 原子及其发现

The idea of atoms dates back to ancient Greek philosophers, but the first scientific model of the atom was proposed by John Dalton in the early 1800s. He described atoms as tiny, indivisible spheres. Later discoveries showed that atoms are actually made of smaller particles.

原子的概念可以追溯到古希腊哲学家，但第一个科学的原子模型是由约翰·道尔顿在19世纪初提出的。他将原子描述为微小、不可再分的球体。后来的发现表明，原子实际上由更小的粒子组成。

J.J. Thomson discovered the electron in 1897 using a cathode ray tube. His “plum pudding” model suggested that electrons were embedded in a positive sphere. Then Ernest Rutherford’s gold foil experiment in 1909 revealed that atoms are mostly empty space with a tiny, dense, positive nucleus.

约瑟夫·约翰·汤姆孙于1897年利用阴极射线管发现了电子。他的“葡萄干布丁”模型认为电子嵌在正电荷球体中。随后，欧内斯特·卢瑟福在1909年的金箔实验揭示，原子大部分是空的空间，中心有一个微小、致密、带正电的原子核。

2. Subatomic Particles | 亚原子粒子

Atoms are composed of three main subatomic particles: protons, neutrons and electrons. Protons and neutrons are found in the nucleus, while electrons move in regions around the nucleus called electron shells (or energy levels).

原子由三种主要的亚原子粒子组成：质子、中子和电子。质子和中子位于原子核中，而电子在原子核周围的区域——称为电子壳层（或能级）——中运动。

Particle	Relative Charge	Relative Mass
Proton	+1	1
Neutron	0	1
Electron	-1	1/1836 (≈0)

In a neutral atom, the number of protons equals the number of electrons. This makes the overall charge zero. The mass of an electron is so tiny that it is usually ignored when calculating the mass of an atom.

在中性原子中，质子数等于电子数，因此总电荷为零。电子的质量非常小，通常在计算原子质量时被忽略不计。

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 the element. For example, carbon always has 6 protons, and any atom with 6 protons is carbon.

原子序数（Z）是原子核中的质子数，它决定了元素种类。例如，碳总是有6个质子，任何具有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 calculated by subtracting the atomic number from the mass number: neutrons = A – Z.

质量数（A）是原子核中质子与中子的总数。中子数可以通过质量数减去原子序数来计算：中子数 = A – Z。

Neutrons = Mass Number − Atomic Number

中子数 = 质量数 − 原子序数

We write the symbol of an element with the mass number as a superscript and the atomic number as a subscript, for example: ²⁴Mg₁₂ or ¹²C₆.

我们用质量数作为上标、原子序数作为下标来表示元素的符号，例如：²⁴Mg₁₂ 或 ¹²C₆。

4. 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不同原子，它们具有相同的质子数但不同的中子数。这意味着它们具有相同的原子序数，但质量数不同。

For example, carbon has three naturally occurring isotopes: carbon-12 (⁶p + ⁶n), carbon-13 (⁶p + ⁷n) and carbon-14 (⁶p + ⁸n). They all behave the same chemically because they have the same number of electrons.

例如，碳有三种天然存在的同位素：碳-12（6个质子+6个中子）、碳-13（6个质子+7个中子）和碳-14（6个质子+8个中子）。由于它们具有相同的电子数，所以化学性质相同。

Isotopes are used in many applications. Carbon-14 is used in radiocarbon dating, while radioactive isotopes such as iodine-131 are used in medicine to treat thyroid conditions.

同位素在许多应用中都有用途。碳-14用于放射性碳定年法，而像碘-131这样的放射性同位素在医学中用于治疗甲状腺疾病。

5. Electronic Configuration | 电子排布

Electrons are arranged in shells around the nucleus. Each shell can hold a limited number of electrons. The first shell holds a maximum of 2 electrons, the second shell holds up to 8, and the third shell also holds up to 8 (for the first 20 elements).

电子围绕原子核排列在壳层中。每个壳层能容纳有限数量的电子。第一层最多容纳2个电子，第二层最多8个，第三层最多8个（对前20号元素而言）。

The electron configuration of an atom shows how its electrons are distributed among the shells. For example, sodium (Na) has 11 electrons, so its configuration is 2, 8, 1. We can write it as 2·8·1 or using shell notation: (2,8,1).

原子的电子排布显示了其电子如何分布在各个壳层中。例如，钠（Na）有11个电子，所以其排布为 2, 8, 1。我们可以写成 2·8·1 或用壳层记号：(2,8,1)。

Na: 2, 8, 1

钠：2, 8, 1

Electrons in the outermost shell are called valence electrons. They determine the chemical properties of an element and how it reacts with other elements.

最外层电子称为价电子。它们决定了元素的化学性质以及它与其他元素反应的方式。

6. Structure of the Periodic Table | 元素周期表的结构

The periodic table arranges all known elements in order of increasing atomic number. Elements are placed in rows called periods and columns called groups. The position of an element is directly linked to its electron configuration.

元素周期表按原子序数递增的顺序排列所有已知元素。元素被放置在称为“周期”的行和称为“族”的列中。元素的位置与其电子排布直接相关。

Elements in the same group have the same number of valence electrons, so they show similar chemical properties. For example, Group 1 elements all have one valence electron, and Group 7 elements all have seven valence electrons.

同一族的元素具有相同的价电子数，因此显示出相似的化学性质。例如，第1族元素都有1个价电子，第7族元素都有7个价电子。

The number of periods tells us how many shells are occupied. For instance, an element in period 3 has three electron shells.

周期数告诉我们占据的电子壳层数。例如，第三周期的元素有三个电子壳层。

7. Groups and Periods – Key Facts | 族和周期——关键事实

Group 1 elements (Li, Na, K, etc.) are called alkali metals. They are soft, have low densities, and react vigorously with water to produce hydrogen gas and an alkaline solution.

第1族元素（锂、钠、钾等）称为碱金属。它们质地柔软、密度低，能与水剧烈反应生成氢气和碱性溶液。

Group 7 elements (F, Cl, Br, I) are called halogens. They are non-metals with increasing boiling points as you go down the group. Their reactivity decreases down the group.

第7族元素（氟、氯、溴、碘）称为卤素。它们是非金属，随着往下移动沸点逐渐增加。其反应活性随族往下递减。

Group 0 elements (He, Ne, Ar) are called noble gases. They are unreactive because they have full outer shells. Helium has 2 outer electrons; neon and argon have 8.

第0族元素（氦、氖、氩）称为稀有气体。由于它们具有充满的外壳层，因此不活泼。氦有2个外层电子；氖和氩有8个。

Period number = number of electron shells

周期数 = 电子壳层数
Group number = number of valence electrons (for groups 1–2 and 3–8 for representative elements)

族数 = 价电子数（对于第1–2族和3–8族的代表性元素）

8. Metals and Non-metals | 金属与非金属

The periodic table can be roughly divided into metals (on the left) and non-metals (on the right). Most elements are metals. Metals tend to lose electrons to form positive ions, while non-metals tend to gain electrons to form negative ions.

元素周期表大致可分为金属（左侧）和非金属（右侧）。大多数元素是金属。金属倾向于失去电子形成正离子，而非金属倾向于获得电子形成负离子。

Metals are usually shiny, malleable, ductile, and good conductors of heat and electricity. Non-metals are often dull, brittle, and poor conductors. However, graphite is an exception – it is a non-metal that conducts electricity.

金属通常有光泽、可延展、可锻且是良好的热和电导体。非金属通常暗淡、易碎且不善于传导。然而，石墨是个例外——它是一种导电的非金属。

The staircase line between metals and non-metals helps us predict the type of element. Elements near the line, like silicon and germanium, are called metalloids and have intermediate properties.

金属与非金属之间的阶梯线帮助我们预测元素的类型。靠近该线的元素，如硅和锗，被称为类金属，具有中间性质。

9. Trends in Period 3 | 第三周期的趋势

In period 3 (Na, Mg, Al, Si, P, S, Cl, Ar), we see trends across the period. As we move from left to right, the number of protons increases, so the nucleus attracts electrons more strongly. This causes atomic radius to decrease across the period.

在第三周期（Na、Mg、Al、Si、P、S、Cl、Ar）中，我们观察到了跨周期的趋势。从左向右移动时，质子数增加，因此原子核对电子的吸引力更强。这导致原子半径沿周期递减。

Ionisation energy generally increases across the period because it becomes harder to remove an electron. Metallic character decreases, and non-metallic character increases. The elements change from metals (Na, Mg, Al) to metalloid (Si) and then to non-metals (P, S, Cl, Ar).

电离能通常沿周期增加，因为失去电子变得更加困难。金属性减弱，非金属性增强。元素从金属（Na、Mg、Al）变为类金属（Si），再变为非金属（P、S、Cl、Ar）。

10. Why the Periodic Table Matters | 元素周期表为何重要

The periodic table is more than a list – it is a powerful tool for predicting properties. By knowing an element’s position, we can predict its reactivity, the types of compounds it forms, and even its physical state at room temperature.

元素周期表不仅仅是一个列表——它是一个预测性质的有力工具。通过了解元素的位置，我们可以预测其反应活性、形成的化合物类型，甚至其在室温下的物理状态。

For example, elements in group 1 all form compounds with valency +1, while group 2 elements form valency +2. This pattern helps chemists balance equations and understand reactions.

例如，第1族元素都形成+1价的化合物，而第2族元素形成+2价。这种规律帮助化学家配平方程式和理解反应。

In the Edexcel IGCSE Science exam, you may be asked to draw the electronic configuration of an element, identify an element from its position, or explain trends in the periodic table. Practice these skills with past paper questions to build confidence.

在 Edexcel IGCSE 科学考试中，你可能会被要求画出某一元素的电子排布、根据位置识别元素，或解释周期表中的趋势。通过练习历年真题来掌握这些技能，以增强信心。

Published by TutorHao | Science Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）

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