Atomic Structure | 原子结构

📚 Atomic Structure | 原子结构

Atoms are the fundamental building blocks of all matter. Understanding their structure is essential for explaining chemical reactions, bonding, and the behaviour of elements in the Periodic Table.

原子是所有物质的基本组成单位。理解原子的结构，是解释化学反应、化学键以及元素在周期表中行为的关键基础。

1. The Subatomic Particles | 亚原子粒子

An atom is composed of three main subatomic particles: protons, neutrons and electrons. Protons carry a positive charge, neutrons carry no charge, and electrons carry a negative charge.

原子由三种主要亚原子粒子组成：质子、中子和电子。质子带正电荷，中子不带电荷，电子带负电荷。

Proton: relative mass 1, relative charge +1.

质子：相对质量 1，相对电荷 +1。
Neutron: relative mass 1, relative charge 0.

中子：相对质量 1，相对电荷 0。
Electron: relative mass 1/1840, relative charge -1.

电子：相对质量 1/1840，相对电荷 -1。

2. Nuclear Model | 核模型

In the nuclear model, protons and neutrons are located in a tiny central nucleus. Electrons move in energy levels (shells) around the nucleus at relatively large distances.

在核模型中，质子和中子位于极小的原子核内。电子则在离核较远的能级（电子层）中运动。

The nucleus is positively charged and contains nearly all of the atom’s mass, even though it occupies a very small volume.

原子核带正电，几乎集中了原子的全部质量，尽管它只占据了很小的体积。

3. 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. The mass number (A) is the total number of protons and neutrons.

原子序数（Z）是原子中质子的数目，它决定了元素的种类。质量数（A）是质子数与中子数之和。

Mass number A = number of protons (Z) + number of neutrons

质量数 A = 质子数（Z）+ 中子数

4. Notation of Nuclides | 核素符号

A nuclide is represented by its element symbol with the mass number written as a superscript and the atomic number as a subscript on the left-hand side.

核素用元素符号表示，质量数写在左上角，原子序数写在左下角。

¹⁶₈O

Here, the mass number is 16 and the atomic number is 8. The number of neutrons is 16 − 8 = 8.

这里，质量数为 16，原子序数为 8。中子数 = 16 − 8 = 8。

5. Calculating Neutrons | 计算中子数

To find the number of neutrons in an atom, subtract the atomic number from the mass number.

要计算原子中的中子数，用质量数减去原子序数即可。

Particle 粒子	Symbol 符号	Mass number 质量数	Neutrons 中子数
Sodium 钠	²³₁₁Na	23	23 − 11 = 12
Chlorine 氯	³⁵₁₇Cl	35	35 − 17 = 18

6. 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.

同位素是同一元素中质子数相同而中子数不同的原子，因此它们具有相同的原子序数，但质量数不同。

For example, carbon-12 (¹²₆C) and carbon-14 (¹⁴₆C) are both carbon isotopes. They have the same chemical properties, but carbon-14 is unstable and radioactive.

例如，碳-12（¹²₆C）和碳-14（¹⁴₆C）都是碳的同位素。它们具有相同的化学性质，但碳-14不稳定且具有放射性。

7. Electron Shells and Configuration | 电子层与电子排布

Electrons occupy shells at increasing distances from the nucleus. The first shell can hold up to 2 electrons, and the second shell can hold up to 8 electrons.

电子在离核由近及远的电子层中排布。第一层最多容纳 2 个电子，第二层最多容纳 8 个电子。

For the first 20 elements, the third shell can also hold up to 8 electrons before filling the fourth shell.

对于前 20 号元素，第三层最多容纳 8 个电子，然后才填充第四层。

8. Writing Electron Configurations | 书写电子排布

Electron configuration shows how electrons are arranged in shells. For example, the configuration of magnesium (12 electrons) is written as 2,8,2.

电子排布表示电子在各层中的分布。例如，镁（12 个电子）的排布写作 2,8,2。

Sodium (11): 2,8,1. Oxygen (8): 2,6. Neon (10): 2,8.

钠（11）：2,8,1。氧（8）：2,6。氖（10）：2,8。

9. Ions and Electron Configurations | 离子与电子排布

When atoms lose or gain electrons, they form ions. Positive ions (cations) have fewer electrons than protons; negative ions (anions) have more electrons than protons.

当原子失去或获得电子时，就形成了离子。阳离子（正离子）的电子数少于质子数；阴离子（负离子）的电子数多于质子数。

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

例如，钠原子（2,8,1）失去一个电子形成 Na⁺，其排布为 2,8。氯原子（2,8,7）获得一个电子形成 Cl⁻，其排布为 2,8,8。

10. Valence Electrons and Reactivity | 价电子与化学性质

The electrons in the outermost shell are called valence electrons. These determine how an element reacts chemically.

最外层的电子称为价电子，它决定了元素的化学性质。

Elements in the same group of the Periodic Table have the same number of valence electrons, so they show similar chemical behaviour. Noble gases have full outer shells (8), which makes them very stable and unreactive.

周期表中同一族的元素具有相同的价电子数，因此化学性质相似。稀有气体的最外层已达到 8 个电子（稳定结构），因此非常稳定，不易发生反应。

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Atomic Structure | 原子结构