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 atomic structure is the foundation of all chemistry. This article breaks down the key ideas from the Edexcel IGCSE Science specification: the subatomic particles, atomic number, mass number, isotopes, and how the periodic table is arranged.

理解原子结构是所有化学的基础。本文围绕 Edexcel IGCSE 科学考纲中的核心内容展开：亚原子粒子、原子序数、质量数、同位素，以及元素周期表的排列方式。

1. The Three Subatomic Particles | 三种亚原子粒子

An atom is made of protons, neutrons, and electrons. Protons carry a positive charge, neutrons are neutral, and electrons carry a negative charge. Protons and neutrons are packed together in the nucleus, while electrons move in shells around the nucleus.

原子由质子、中子和电子构成。质子带正电荷，中子不带电，电子带负电荷。质子和中子紧密排列在原子核内，而电子则在核外的电子壳层中运动。

Proton: relative mass 1, relative charge +1

质子：相对质量为 1，相对电荷为 +1
Neutron: relative mass 1, relative charge 0

中子：相对质量为 1，相对电荷为 0
Electron: relative mass 1/1836, relative charge -1

电子：相对质量约为 1/1836，相对电荷为 -1

The number of protons defines the element. In a neutral atom, the number of electrons equals the number of protons.

质子数决定了元素的种类。在电中性的原子中，电子数等于质子数。

2. 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. The mass number (A) is the total number of protons and neutrons. You can calculate the number of neutrons using: mass number – atomic number.

原子序数（Z）是原子核中的质子数。质量数（A）是质子和中子总数。中子数可用质量数减去原子序数得到。

Number of neutrons = A – Z

中子数 = 质量数 – 原子序数

For example, a sodium atom has atomic number 11 and mass number 23. It contains 11 protons, 11 electrons, and 12 neutrons.

例如，钠原子原子序数为 11，质量数为 23。它含有 11 个质子、11 个电子和 12 个中子。

3. 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 holds a maximum of 2 electrons, the second and third shells hold up to 8 electrons each. The electronic configuration shows how electrons are arranged.

电子占据核外的电子壳层（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。电子排布表示电子的分布方式。

For example, oxygen has 8 electrons: 2 in the first shell and 6 in the second shell, written as 2.6. Magnesium has 12 electrons: 2.8.2.

例如，氧有 8 个电子：第一层 2 个，第二层 6 个，写作 2.6。镁有 12 个电子：2.8.2。

The electrons in the outermost shell are called valence electrons. They determine the chemical properties of an element.

最外层电子称为价电子，它们决定元素的化学性质。

4. Isotopes | 同位素

Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons. They have the same atomic number but different mass numbers.

同位素是同一元素的不同原子，它们质子数相同而中子数不同。因此它们原子序数相同，质量数不同。

Carbon-12 and carbon-14 are isotopes of carbon. Both have 6 protons, but carbon-12 has 6 neutrons and carbon-14 has 8 neutrons.

碳-12 和碳-14 是碳的同位素。两者都有 6 个质子，但碳-12 有 6 个中子，碳-14 有 8 个中子。

Isotopes have identical chemical properties because they have the same electronic configuration. However, they may have different physical properties, such as mass or density.

同位素的化学性质相同，因为它们具有相同的电子排布。但它们的物理性质可能不同，如质量或密度。

5. Relative Atomic Mass and Relative Isotopic Mass | 相对原子质量与相对同位素质量

The relative atomic mass (Aᵣ) is the weighted average mass of an element’s isotopes compared with 1/12 the mass of a carbon-12 atom. It is not a whole number because it accounts for the natural abundance of each isotope.

相对原子质量（Aᵣ）是元素各同位素的加权平均质量，以碳-12 原子质量的 1/12 为标准。它通常不是整数，因为要考虑各同位素的天然丰度。

For chlorine, the relative atomic mass is about 35.5 because chlorine has two main isotopes: chlorine-35 (about 75%) and chlorine-37 (about 25%).

例如氯的相对原子质量约为 35.5，因为氯有两种主要同位素：氯-35（约占 75%）和氯-37（约占 25%）。

Aᵣ = Σ(isotopic mass × abundance) / total abundance

相对原子质量 = Σ（同位素质量 × 丰度）÷ 总丰度

6. 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 horizontal row is called a period; a vertical column is called a group. Elements in the same group have the same number of valence electrons, so they have similar chemical properties.

元素周期表按原子序数递增排列。横行称为周期，纵列称为族。同一族的元素具有相同的价电子数，因此化学性质相似。

Group 1 elements (alkali metals) have 1 valence electron and are highly reactive metals. Group 7 elements (halogens) have 7 valence electrons and are reactive non-metals. Group 0 elements (noble gases) have full outer shells and are unreactive.

第 1 族元素（碱金属）有 1 个价电子，是非常活泼的金属。第 7 族元素（卤素）有 7 个价电子，是活泼的非金属。第 0 族元素（稀有气体）具有满电子外层，非常不活泼。

7. Metals and Non-metals in the Periodic Table | 周期表中的金属与非金属

Metals are found on the left and in the middle of the periodic table. Non-metals are found on the right. The dividing line is a diagonal staircase from boron to polonium.

金属位于周期表的左侧和中部。非金属位于右侧。两者之间有一条从硼到钋的对角线分界。

Metals: shiny, malleable, good conductors of heat and electricity, high melting points

金属：有光泽、可延展、良好的热和电导体、熔点较高
Non-metals: dull, brittle, poor conductors, low melting points

非金属：暗淡、易碎、导电导热差、熔点较低

Some elements, such as carbon and silicon, have properties of both metals and non-metals.

一些元素如碳和硅，同时具有金属和非金属的性质。

8. Group 1: Alkali Metals | 第 1 族：碱金属

The alkali metals are lithium, sodium, potassium, rubidium, caesium, and francium. They are soft, low-density metals that react vigorously with water to produce hydrogen gas and an alkaline solution.

碱金属包括锂、钠、钾、铷、铯和钫。它们都是柔软、密度低的金属，能与水剧烈反应生成氢气和碱性溶液。

Reactivity increases down the group. This is because the outer electron is further from the nucleus and is more easily lost.

同族中从上到下反应活性增强。这是因为最外层电子离核越来越远，更容易失去。

2Na + 2H₂O → 2NaOH + H₂

9. Group 7: Halogens | 第 7 族：卤素

Halogens include fluorine, chlorine, bromine, iodine, and astatine. They are non-metals that exist as diatomic molecules (F₂, Cl₂, Br₂, I₂). Their reactivity decreases down the group.

卤素包括氟、氯、溴、碘和砹。它们是非金属，以双原子分子形式存在（F₂、Cl₂、Br₂、I₂）。同族中从上到下反应活性减弱。

At room temperature, chlorine is a greenish gas, bromine is a reddish-brown liquid, and iodine is a grey-black solid. These trends reflect increasing molecular size and stronger van der Waals forces.

室温下，氯是黄绿色气体，溴是红棕色液体，碘是灰黑色固体。这些趋势反映了分子尺寸增大和范德华力增强。

10. Group 0: Noble Gases | 第 0 族：稀有气体

Noble gases are helium, neon, argon, krypton, xenon, and radon. They are all monatomic gases with a full outer shell of electrons. This gives them very low reactivity – they are inert.

稀有气体包括氦、氖、氩、氪、氙和氡。它们都是单原子气体，具有全满的外层电子。这使得它们反应性极低，性质不活泼。

As you go down the group, the boiling points increase because the atoms become larger and stronger intermolecular forces form.

同族中从上到下沸点升高，因为原子变大，分子间作用力增强。

11. Group Trends Summary | 族趋势总结

In Group 1, atomic radius increases down the group and electronegativity decreases. In Group 7, atomic radius increases down the group but reactivity decreases. In Group 0, boiling point increases down the group.

在第 1 族中，原子半径从上到下增大，电负性减小。在第 7 族中，原子半径从上到下增大，但反应活性降低。在第 0 族中，沸点从上到下升高。

Understanding these trends helps predict the properties of unfamiliar elements and is a key skill in the IGCSE exam.

理解这些趋势有助于预测不熟悉元素的性质，这也是 IGCSE 考试中的关键技能。

12. Exam Tips: Working with Atomic Structure | 考试技巧：原子结构题解法

Always read the mass number and atomic number from the notation. Remember that electrons are arranged in shells and the outer shell determines reactivity. When calculating relative atomic mass, use the percentage abundance as the weighting factor.

务必从元素符号中读取质量数和原子序数。牢记电子按壳层排列，最外层电子决定反应活性。计算相对原子质量时，以百分丰度作为权重。

When drawing atoms, show the nucleus with protons and neutrons, and draw electrons as dots or crosses in the correct shells. Double-check that the total number of electrons equals the atomic number.

画原子示意图时，在原子核中标出质子和中子，并用小点或叉号在正确的壳层中画出电子。反复检查电子总数是否等于原子序数。

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