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 article covers the core ideas of atomic structure and the periodic table for Edexcel IGCSE Science. You will learn how atoms are built, how to use atomic and mass numbers, and how the periodic table organises elements by their electronic structure.

本文面向 Edexcel IGCSE 科学课程，系统讲解原子结构与元素周期表的核心概念。你将学习原子的构成、如何运用原子序数和质量数，以及元素周期表如何按照电子排布对元素进行组织。

1. Structure of an Atom | 原子结构

An atom is the smallest part of an element that can exist. It consists of a central nucleus surrounded by electrons. The nucleus contains protons and neutrons, which are collectively called nucleons.

原子是元素存在的最小微粒。它由位于中心的原子核以及围绕核运动的电子组成。原子核内含有质子和中子，它们统称为核子。

Protons are positively charged particles found in the nucleus.

质子是位于原子核内带正电的粒子。
Neutrons have no charge and also lie in the nucleus.

中子不带电，同样位于原子核内。
Electrons are negatively charged and move around the nucleus in shells.

电子带负电，在原子核外的电子壳层中运动。

proton charge = +1, electron charge = −1, neutron charge = 0

质子电荷 = +1，电子电荷 = −1，中子电荷 = 0

2. 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 which element the atom belongs to. In a neutral atom, the number of electrons equals the number of protons.

原子序数（Z）是指原子中质子的数目。它决定了该原子属于哪种元素。在电中性的原子中，电子数目等于质子数目。

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

质量数（A）是指原子核中质子与中子的总数。

mass number = number of protons + number of neutrons

质量数 = 质子数 + 中子数

For example, a sodium atom has atomic number 11 and mass number 23, so 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，因此含有 11 个质子、11 个电子和 12 个中子。

3. Isotopes | 同位素

Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. They therefore 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。因此，它们具有相同的原子序数，但质量数不同。

Isotope	Protons	Neutrons	Mass number
Carbon-12	6	6	12
Carbon-14	6	8	14

Isotopes have the same chemical properties because they have the same electronic configuration. However, their physical properties may differ, for example in mass and density.

同位素具有相同的化学性质，因为它们的电子排布相同。然而，它们的物理性质可能不同，例如质量和密度不同。

4. Electronic Configuration | 电子排布

Electrons occupy energy levels, also called shells, around the nucleus. The lowest energy shell is filled first. Each shell can hold a maximum number of electrons: shell 1 holds 2, shell 2 holds 8, shell 3 holds 8 (for the first 18 elements).

电子占据原子核周围的能级，也称为电子壳层。能量最低的壳层最先被填满。每个壳层可容纳的电子数有上限：第一层可容纳 2 个，第二层 8 个，第三层 8 个（对于前 18 号元素）。

For example, magnesium (atomic number 12) has the electron arrangement 2, 8, 2. This tells us that it has 2 electrons in the first shell, 8 in the second shell and 2 in the third shell.

例如，镁（原子序数 12）的电子排布为 2, 8, 2。这表示其第一壳层有 2 个电子，第二壳层有 8 个电子，第三壳层有 2 个电子。

The number of electrons in the outer shell is called the valence electrons. These electrons determine how the atom reacts chemically.

最外层电子数称为价电子数。这些电子决定了原子的化学性质。

5. The Periodic Table | 元素周期表

The periodic table arranges all known elements in order of increasing atomic number. Elements are placed in vertical columns called groups and horizontal rows called periods.

元素周期表按照原子序数递增的顺序排列所有已知元素。元素被放置在称为族的纵列和称为周期的横行中。

Each box in the periodic table usually shows the atomic number, the symbol and the relative atomic mass of the element.

周期表中的每个格通常显示该元素的原子序数、元素符号和相对原子质量。

Period number = number of occupied shells; Group number = number of valence electrons (for Groups 1 and 2)

周期数 = 电子壳层数；主族序号 = 最外层电子数（对于第 1 和第 2 族）

6. Groups and Periods | 族和周期

A group is a vertical column. Elements in the same group have the same number of outer-shell electrons, so they have similar chemical properties.

族是周期表中的纵列。同一族中的元素具有相同的最外层电子数，因此它们的化学性质相似。

A period is a horizontal row. Elements in the same period have the same number of electron shells. For example, all elements in Period 3 have three occupied shells.

周期是周期表中的横行。同一周期内的元素具有相同的电子壳层数。例如，第三周期的所有元素都有三个电子壳层。

As you move across a period from left to right, the atomic number increases by one each time and the electronic configuration changes systematically.

当从左向右横穿一个周期时，原子序数逐一增加，电子排布也发生有规律的变化。

7. Trends in the Periodic Table | 元素周期表中的规律

Across a period, the number of protons increases, so the positive charge of the nucleus increases. The electrons are held more tightly, so atomic size generally decreases across a period.

在同一周期中，质子数目增加，导致原子核正电荷增加。核对电子的吸引增强，因此原子大小总体上随周期从左到右而减小。

Down a group, each element has an extra electron shell. The outer electrons are farther from the nucleus and are shielded by inner shells, so atomic size increases down a group.

在同一个族中，每个元素比上一个元素多一个电子壳层。最外层电子离核更远，且被内层电子屏蔽，因此原子大小随族从上到下而增大。

Across a period, elements go from metallic to non-metallic character.

横穿周期时，元素由金属性逐渐过渡到非金属性。
Down a group, metallic character increases for Groups 1 and 2.

对于第 1 族和第 2 族，自上而下金属性增强。

8. Metals and Non-metals | 金属与非金属

Metals are found on the left and middle of the periodic table. They are shiny, conduct electricity well, are malleable and have high melting points in general.

金属位于周期表的左侧和中部。它们具有金属光泽，导电性强，具有延展性，通常熔点较高。

Non-metals are found on the right side of the periodic table. They are poor conductors of electricity, are dull, and exist as solids or gases at room temperature (except bromine, which is a liquid).

非金属位于周期表的右侧。它们不善于导电，外观暗淡，在室温下以固体或气体形式存在（溴除外，它是液体）。

Metals tend to lose electrons to form positive ions, while non-metals tend to gain electrons to form negative ions.

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。

9. Group 1: Alkali Metals | 第 1 族：碱金属

Group 1 elements are called the alkali metals. They include lithium, sodium and potassium. They all have one electron in their outer shell.

第 1 族元素被称为碱金属，包括锂、钠和钾。它们的最外层都有一个电子。

Alkali metals are soft, have relatively low melting points, and react with water to produce hydrogen gas and an alkaline solution.

碱金属质地软，熔点相对较低，与水反应生成氢气和碱性溶液。

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

碱金属的活泼性随原子序数增大而增强，因为最外层电子离核更远，更容易失去。

2Na + 2H₂O → 2NaOH + H₂

10. Group 7: Halogens | 第 7 族：卤素

Group 7 elements are called the halogens. They include fluorine, chlorine, bromine and iodine. They all have seven electrons in their outer shell.

第 7 族元素被称为卤素，包括氟、氯、溴和碘。它们的最外层都有七个电子。

Halogens are non-metals. Their reactivity decreases down the group, because the atoms get larger and it becomes harder to gain an additional electron.

卤素是非金属。它们的活泼性随原子序数增大而减弱，因为原子变大，获得额外电子变得更困难。

Halogens form diatomic molecules, such as Cl₂ and Br₂. They react with metals to form salts, for example sodium chloride.

卤素形成双原子分子，例如 Cl₂ 和 Br₂。它们与金属反应生成盐，例如氯化钠。

11. Group 0: Noble Gases | 第 0 族：稀有气体

Group 0 elements are the noble gases: helium, neon, argon, krypton and xenon. They have full outer shells, so they are very stable and unreactive.

第 0 族元素是稀有气体，包括氦、氖、氩、氪和氙。它们具有全满的最外层电子壳层，因此非常稳定，不易发生反应。

Noble gases exist as single atoms and are colourless gases at room temperature. Their boiling points increase down the group as the size of the atoms increases.

稀有气体以单原子形式存在，在室温下是无色气体。它们的沸点随原子序数增大而升高，因为原子体积增大。

Because they are unreactive, noble gases are used in filling balloons and in providing an inert atmosphere for welding.

由于稀有气体不活泼，它们可用于填充气球以及为焊接提供惰性气氛。

12. Summary of Key Ideas | 核心要点总结

In this article, we have covered the basics of atomic structure, isotopes, electronic configuration and the periodic table. Remember that the atomic number is the number of protons, and the mass number is the sum of protons and neutrons.

在本文中，我们学习了原子结构、同位素、电子排布以及元素周期表的基础知识。请记住：原子序数是质子数，质量数是质子数与中子数之和。

Elements in the same group have similar chemical properties because they have the same number of outer-shell electrons. Elements in the same period have the same number of electron shells.

同一族元素具有相似的化学性质，因为它们的最外层电子数相同。同一周期元素具有相同的电子壳层数。

Practise drawing the electron configuration for the first 20 elements, and compare the trends in Groups 1, 7 and 0. This will help you answer many exam questions confidently.

请练习画出前 20 号元素的电子排布，并比较第 1 族、第 7 族和第 0 族的规律。这将帮助你自信地回答许多考试题目。

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