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

In this revision guide, we will cover the fundamentals of atomic structure and the periodic table for the Edexcel IGCSE Science (Double Award) course. You will learn about the particles that make up an atom, how electrons are arranged, and the patterns that organise the elements. This knowledge is essential for understanding chemical behaviour and for succeeding in your exams.

在本复习指南中，我们将涵盖 Edexcel IGCSE 科学（双奖）课程中原子结构和元素周期表的基础知识。你将了解组成原子的微粒、电子的排布方式以及元素组织的规律。这些知识对于理解化学行为和考试取得好成绩至关重要。

1. The Basic Structure of an Atom | 原子的基本结构

Every atom consists of a tiny, dense nucleus surrounded by a cloud of electrons. The nucleus contains protons and neutrons, which are collectively called nucleons. The electrons move in energy levels around the nucleus at very high speeds, occupying most of the atom’s volume.

每个原子都由一个微小而致密的原子核和围绕核的电子云组成。原子核中含有质子和中子，它们统称为核子。电子在核外高速运动，占据原子大部分体积，并排列在不同的能级上。

The nucleus is positively charged because of the protons.
Electrons are negatively charged and have almost no mass.
Neutrons have no charge and a mass slightly larger than protons.

原子核因质子而带正电。
电子带负电，质量几乎为零。
中子不带电，质量略大于质子。

2. Properties of Subatomic Particles | 亚原子粒子的性质

It is essential to know the relative mass and relative charge of the three subatomic particles. These values are provided in the exam, but memorising them saves time and reduces errors.

掌握三种亚原子粒子的相对质量和相对电荷至关重要。考试中会给出这些数值，但记住它们可以节省时间并减少错误。

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

From this table, you can see that protons and neutrons carry almost all the mass of an atom, while electrons contribute very little.

从这个表格可以看出，质子和中子承担了原子几乎全部的质量，而电子的贡献非常小。

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 is. 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。它决定了这个原子属于哪种元素。质量数（A）是原子核中质子数和中子数的总和。

Number of protons = atomic number
Number of electrons in a neutral atom = atomic number
Number of neutrons = mass number – atomic number

质子数 = 原子序数
中性原子中电子数 = 原子序数
中子数 = 质量数 – 原子序数

For an atom X with mass number A and atomic number Z: ₐ X ⁿ? No, use standard notation: ᴬᵦX? Let’s use simple notation: X with A above and Z below.

For example, carbon-12 has A = 12 and Z = 6, so it contains 6 protons, 6 neutrons and 6 electrons.

例如，碳-12 的 A = 12, Z = 6，因此它含有 6 个质子、6 个中子和 6 个电子。

⁶C¹²? Actually: ¹²₆C

Here, the mass number is written as a superscript left of the symbol, and the atomic number as a subscript left.

这里，质量数写在符号的左上角，原子序数写在符号的左下角。

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.

同位素是同一元素的原子，它们具有相同的质子数，但具有不同的中子数。因此，它们的原子序数相同，但质量数不同。

For example, hydrogen has three isotopes: protium (¹H), deuterium (²H), and tritium (³H). All have one proton, but they contain zero, one and two neutrons respectively.

例如，氢有三种同位素：氕（¹H）、氘（²H）和氚（³H）。它们都有一个质子，但中子数分别为零、一和二。

Isotopes have the same chemical properties because they have the same electron arrangement.
Isotopes have different physical properties, such as density and mass.
Isotopes can be radioactive, which is useful in medicine and carbon dating.

同位素具有相同的化学性质，因为它们的电子排布相同。
同位素具有不同的物理性质，如密度和质量。
同位素可能具有放射性，可用于医学和碳定年。

5. Electron Shells and Energy Levels | 电子壳层与能级

Electrons are arranged in shells (energy levels) around the nucleus. Each shell can hold a maximum number of electrons. The first shell holds up to 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（能级）中。每个壳层能容纳的最大电子数是有限的。第一壳层最多容纳 2 个电子，第二壳层最多容纳 8 个，第三壳层最多也可容纳 8 个（对于前 20 号元素）。

Maximum electrons = 2n²

where n is the shell number. So, shell 1: 2 × 1² = 2; shell 2: 2 × 2² = 8; shell 3: 2 × 3² = 18, but for IGCSE, only the first two and the outer shell are considered.

其中 n 是壳层编号。因此，第 1 壳层：2 × 1² = 2；第 2 壳层：2 × 2² = 8；第 3 壳层：2 × 3² = 18，但在 IGCSE 中，只考虑前两个壳层和最外层。

Electrons fill the lowest-energy shells first. The outermost shell is called the valence shell, and electrons there are called valence electrons.

电子首先填充能量最低的壳层。最外层称为价壳层，其中的电子称为价电子。

6. Writing Electron Configurations | 书写电子排布式

You must be able to write the electronic configuration for the first 20 elements. A simple way is to use numbers and letters, for example 2.8.1 for sodium (11 electrons). Alternatively, you can write 2,8,1.

你必须能够写出前 20 号元素的电子排布式。一种简单的方法是使用数字和圆点，例如钠（11 个电子）为 2.8.1。也可以写成 2,8,1。

For example:

Oxygen (8 electrons): 2,6
Magnesium (12 electrons): 2,8,2
Chlorine (17 electrons): 2,8,7
Potassium (19 electrons): 2,8,8,1

例如：

氧（8 个电子）：2,6
镁（12 个电子）：2,8,2
氯（17 个电子）：2,8,7
钾（19 个电子）：2,8,8,1

Notice that the last shell is the highest energy level that contains electrons.

注意，最后一个数字代表含有电子的最高能级。

7. The Layout of the Periodic Table | 元素周期表的布局

The periodic table arranges elements in order of increasing atomic number. There are rows called periods and columns called groups. There are 7 periods and 8 main groups (I to VIII, or 1 to 18 using modern numbering).

元素周期表按原子序数递增排列。行称为周期，列称为族。共有 7 个周期和 8 个主族（I 至 VIII，或使用现代编号 1 至 18）。

Elements in the same group have the same number of electrons in their outer shell.
Elements in the same group have similar chemical properties.
The group number for main group elements equals the number of valence electrons.

同一族的元素具有相同的最外层电子数。
同一族的元素具有相似的化学性质。
主族元素的族号等于其价电子数。

For example, Group I elements (Li, Na, K) all have 1 outer electron, and Group VII elements (F, Cl, Br) all have 7 outer electrons.

例如，第 I 族元素（Li、Na、K）都只有 1 个外层电子，而第 VII 族元素（F、Cl、Br）都有 7 个外层电子。

8. Trends Across a Period | 周期内的递变规律

Moving from left to right across a period, the atomic number increases and the number of protons increases. Electrons are added to the same shell. As a result, the nucleus attracts the electron cloud more strongly, making the atoms smaller (atomic radius decreases).

在同一周期中从左向右移动，原子序数增加，质子数增加。电子被添加到同一个壳层。因此，原子核对电子云的吸引力更强，使原子半径减小。

Atomic radius decreases across a period.
Electronegativity increases across a period.
Metallic character decreases across a period.

原子半径在同一周期内从左到右逐渐减小。
电负性在同一周期内逐渐增强。
金属性在同一周期内逐渐减弱。

For example, sodium is a metal, while chlorine is a non-metal, even though they are both in period 3.

例如，钠是金属，而氯是非金属，尽管它们都在第三周期。

9. Trends Down a Group | 族内的递变规律

Moving down a group, each element has one more electron shell than the one above. The outer electrons are further from the nucleus and are shielded by inner electron shells. Therefore, the atomic radius increases and the electrons are more easily lost.

在同一族中从上向下，每个元素比上方的元素多一个电子壳层。外层电子离原子核更远，并受到内层电子壳层的屏蔽。因此，原子半径增大，电子更容易失去。

Atomic radius increases down a group.
Ionisation energy generally decreases down a group.
Reactivity trend varies: Group I metals become more reactive down the group, while Group VII non-metals become less reactive down the group.

原子半径在同一族中向下逐渐增大。
电离能通常在同一族中向下逐渐减小。
反应活性趋势不同：第 I 族金属向下越来越活泼，而第 VII 族非金属向下越来越不活泼。

For example, lithium reacts gently with water, but potassium reacts vigorously. Fluorine is more reactive than iodine.

例如，锂与水反应平缓，而钾与水反应剧烈。氟比碘活泼。

10. Metals and Non-metals | 金属与非金属

The periodic table can be roughly divided into metals (left and centre) and non-metals (right). A zigzag line, often called the ‘staircase’, separates them. Elements next to this line, such as silicon, are called metalloids.

元素周期表大致可以分为金属（左侧和中部）和非金属（右侧）。一条锯齿线（通常称为“阶梯线”）将它们分开。紧挨着这条线的元素，如硅，被称为准金属。

Metals: high melting points, good conductors of heat and electricity, malleable, ductile.
Non-metals: low melting points (except carbon and silicon), poor conductors, brittle in solid state.
Metals form basic oxides, while non-metals form acidic oxides.

金属：熔点高，能很好地传导热和电，可延展，有韧性。
非金属：熔点低（碳和硅除外），导电性差，固态时脆。
金属形成碱性氧化物，而非金属形成酸性氧化物。

In chemical reactions, metals tend to lose electrons to form positive ions, while non-metals tend to gain electrons to form negative ions.

在化学反应中，金属容易失去电子形成正离子，而非金属容易得到电子形成负离子。

11. Noble Gases | 稀有气体

Group VIII (or Group 18) elements are the noble gases: helium, neon, argon, krypton, xenon and radon. They have a full outer shell of electrons, making them very stable and unreactive.

第 VIII 族（或第 18 族）元素是稀有气体：氦、氖、氩、氪、氙和氡。它们具有完全充满的外层电子壳层，因此非常稳定，不易发生反应。

They exist as monatomic gases.
They have very low boiling points.
They are used in lighting (neon), welding (argon) and balloons (helium).

它们以单原子气体形式存在。
它们的沸点非常低。
它们可用于照明（氖气）、焊接（氩气）和气球（氦气）。

Because their outer shells are full, noble gases do not easily form compounds. This explains their old name, ‘inert gases’.

由于它们的最外层已经达到满额，稀有气体不容易形成化合物。这解释了它们旧名称“惰性气体”的由来。

12. Summary and Exam Tips | 总结与考试提示

To succeed in the Edexcel IGCSE Science exam, you must be able to recall the structure of the atom, interpret electron configurations, and explain the trends in the periodic table. Common exam questions ask you to compare isotopes or explain why elements in the same group have similar properties.

要在 Edexcel IGCSE 科学考试中取得成功，你必须能回忆原子的结构、解读电子排布式，并解释元素周期表中的趋势。常见考题要求你比较同位素，或解释为什么同一族的元素具有相似的性质。

Always use the correct notation for isotopes: ¹⁴₆C or ¹²₆C.
Remember that the number of electrons in a neutral atom equals the number of protons.
When writing electron configurations, fill inner shells first.
Be careful with terminology: ‘atomic number’ is protons, not mass.

始终使用正确的同位素符号：¹⁴₆C 或 ¹²₆C。
记住中性原子中的电子数等于质子数。
书写电子排布式时，先填充内层壳层。
注意术语：“原子序数”是质子数，不是质量数。

Revise these topics regularly and practise drawing electron shell diagrams. Working through past papers will help you identify the exact style of questions Edexcel uses.

定期复习这些主题，并练习绘制电子壳层示意图。做历年真题将帮助你识别 Edexcel 出题的确切风格。

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