Atomic Structure & The Periodic Table | 原子结构与元素周期表

📚 Atomic Structure & The Periodic Table | 原子结构与元素周期表

This article provides a comprehensive review of atomic structure and the periodic table for the Edexcel IGCSE Science syllabus. It covers the key definitions, the behaviour of subatomic particles, electron arrangements, and the patterns that explain how elements are organised. Understanding these concepts is essential for tackling exam questions on bonding, chemical reactions, and physical properties.

本文针对 Edexcel IGCSE 科学课程大纲，系统复习原子结构与元素周期表。内容包括关键定义、亚原子粒子的行为、电子排布，以及解释元素如何组织的规律。理解这些概念对于回答有关化学键、化学反应和物理性质的考试题目至关重要。

1. The Atom | 原子

An atom is the smallest particle of an element that retains the chemical properties of that element. It consists of a central nucleus surrounded by electrons. The nucleus is very small and dense, containing protons and neutrons.

原子是保持元素化学性质的最小粒子。它由一个中央原子核和围绕它运动的电子组成。原子核非常小且密度高，包含质子和中子。

Most of the atom is empty space. If an atom were enlarged to the size of a football stadium, the nucleus would be about the size of a pea at the centre.

原子的大部分是空的。如果把一个原子放大到足球场那么大，原子核大约只有中心的一粒豌豆大小。

Protons are positively charged.

质子带正电荷。
Neutrons have no charge (they are neutral).

中子不带电荷（呈电中性）。
Electrons are negatively charged and move around the nucleus in shells.

电子带负电荷，在原子核外的壳层中运动。

2. Subatomic Particles | 亚原子粒子

There are three main subatomic particles. Their relative masses and charges must be memorised for the IGCSE exam.

主要有三种亚原子粒子。它们的相对质量和相对电荷必须在 IGCSE 考试中记住。

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

The charge on an electron is equal in size to the charge on a proton, but opposite in sign. Atoms are electrically neutral because they contain equal numbers of protons and electrons.

电子所带的电荷与质子电荷大小相等、符号相反。原子呈电中性，因为它们含有相同数量的质子和电子。

Number of protons = Number of electrons (in a neutral atom)

质子数 = 电子数（对于中性原子）

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 belongs to. For example, all carbon atoms have 6 protons, so carbon has atomic number 6.

原子序数（Z）是原子核中的质子数。它确定了这个原子属于哪种元素。例如，所有碳原子都有 6 个质子，所以碳的原子序数是 6。

The mass number (A) is the total number of protons and neutrons in the nucleus. The number of neutrons is therefore found by subtracting the atomic number from the mass number.

质量数（A）是原子核中质子与中子的总数。因此，中子的数目可以通过质量数减去原子序数得到。

Mass number = Atomic number + Number of neutrons

质量数 = 原子序数 + 中子数

For a sodium atom with 11 protons and 12 neutrons, the atomic number is 11 and the mass number is 23. This can be written as sodium-23 or ²³Na.

对于含有 11 个质子和 12 个中子的钠原子，原子序数是 11，质量数是 23。这可以写成 sodium-23 或 ²³Na。

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.

同位素是同一元素中具有相同质子数但不同中子数的原子。这意味着它们具有相同的原子序数，但质量数不同。

For example, hydrogen has three common isotopes: protium (¹H), deuterium (²H), and tritium (³H). All have one proton, but they have 0, 1, and 2 neutrons respectively.

例如，氢有三种常见同位素：氕（¹H）、氘（²H）和氚（³H）。它们都有一个质子，但分别有 0、1 和 2 个中子。

Isotopes of the same element have the same chemical properties because they have the same number of electrons, but they may have different physical properties such as density and rate of diffusion.

同一元素的同位素具有相同的化学性质，因为它们具有相同的电子数，但它们可能具有不同的物理性质，例如密度和扩散速率。

5. Electron Shells | 电子壳层

Electrons orbit the nucleus in energy levels called shells or principal energy levels. Each shell can hold a maximum number of electrons. The first shell can hold 2 electrons, the second shell can hold 8, and the third shell can also hold 8 (for the first 18 elements).

电子在称为壳层或主能级的能级中围绕原子核运行。每个壳层可以容纳最大数目的电子。第一层最多容纳 2 个电子，第二层最多容纳 8 个，第三层（对于前 18 号元素）也最多容纳 8 个。

Shell number (n) maximum electrons = 2n²

第 n 层最大电子数 = 2n²

The outermost shell is called the valence shell. The electrons in it are called valence electrons. These electrons are responsible for chemical bonding and reactivity.

最外层被称为价电子层。其中的电子被称为价电子。这些电子负责化学键和化学活性。

6. Electron Configuration | 电子排布

Electron configuration describes how electrons are arranged in shells. The Edexcel IGCSE syllabus requires you to write electron configurations for the first 20 elements.

电子排布描述了电子在壳层中的排列方式。Edexcel IGCSE 大纲要求你写出前 20 号元素的电子排布。

Rules: fill the first shell first, then the second, then the third, and so on. For example, oxygen (8 electrons) fills the first shell with 2 electrons and the second shell with 6 electrons. Its configuration is written as 2,6.

规则：先填满第一层，再填第二层，然后第三层，依此类推。例如，氧（8 个电子）第一层填 2 个，第二层填 6 个。它的排布写作 2,6。

For potassium (19 electrons), the configuration is 2,8,8,1. Note that the third shell can hold 8 electrons before the fourth shell starts filling, for calcium and potassium.

对于钾（19 个电子），排布为 2,8,8,1。注意对于钾和钙，第三层最多容纳 8 个电子后，第四层才开始填入。

Helium: 2

氦：2
Carbon: 2,4

碳：2,4
Sodium: 2,8,1

钠：2,8,1
Chlorine: 2,8,7

氯：2,8,7

7. The Periodic Table | 元素周期表

The periodic table arranges all known elements in order of increasing atomic number. It is divided into rows called periods and columns called groups. Elements in the same group have similar chemical properties.

元素周期表按原子序数递增的顺序排列所有已知元素。它分为称为周期的横行和称为族的纵列。同一族的元素具有相似的化学性质。

The periodic table also shows each element’s symbol, atomic number, and relative atomic mass. In most tables, the atomic number is written above the symbol, and the relative atomic mass is written below.

元素周期表还显示每个元素的符号、原子序数和相对原子质量。在大多数表中，原子序数写在符号上方，相对原子质量写在下方。

Elements are placed into groups based on the number of electrons in their outer shell. For groups 1, 2, and 13-18, the group number (using the old IGCSE system) is equal to the number of outer electrons.

元素根据最外层电子数分入各族。对于第 1、2 和 13-18 族（使用旧 IGCSE 体系），族号等于最外层电子数。

8. Groups and Periods | 族与周期

A group is a vertical column in the periodic table. Elements in the same group have the same number of outer electrons and similar chemical properties. A period is a horizontal row. Elements in the same period have the same number of occupied shells.

族是周期表中的纵列。同一族的元素具有相同的最外层电子数和相似的化学性质。周期是横行。同一周期的元素具有相同的电子壳层数。

Group 1 elements (alkali metals) have 1 outer electron. Group 2 elements (alkaline earth metals) have 2 outer electrons. Group 7 elements (halogens) have 7 outer electrons. Group 0 elements (noble gases) have a full outer shell (2 or 8 electrons).

第 1 族元素（碱金属）有 1 个外层电子。第 2 族元素（碱土金属）有 2 个外层电子。第 7 族元素（卤素）有 7 个外层电子。第 0 族元素（稀有气体）具有全满的外层（2 或 8 个电子）。

Going down a group, the atoms get larger and the number of shells increases. Their reactivity changes in a predictable way: group 1 metals become more reactive down the group, while group 7 non-metals become less reactive down the group.

在族中向下移动时，原子变大，壳层数增加。它们的活性以可预测的方式变化：第 1 族金属向下反应性增强，而第 7 族非金属向下反应性减弱。

9. Metals and Non-Metals | 金属与非金属

The periodic table is roughly divided into metals on the left and non-metals on the right, with a zig-zag line separating them. Metals tend to be shiny, conductive, malleable, and ductile. Non-metals are usually dull, brittle, and poor conductors.

元素周期表大致分为左侧的金属和右侧的非金属，它们之间以一条锯齿线分隔。金属通常有光泽、能导电、可锻造、可拉伸。非金属通常暗淡、易碎，且导电性差。

Metals lose electrons to form positive ions, while non-metals gain electrons to form negative ions. This difference explains many of the trends in the periodic table.

金属失去电子形成正离子，而非金属获得电子形成负离子。这种差异解释了周期表中的许多递变规律。

Metals are found in groups 1, 2, and the transition metals in the middle. Non-metals are found in groups 15, 16, 17, and 0, as well as hydrogen at the top of group 1.

金属位于第 1、2 族和中间的过渡金属区域。非金属位于第 15、16、17、0 族，以及第 1 族顶部的氢。

10. Trends in the Periodic Table | 周期表中的递变规律

Across a period, the number of protons increases, so the positive charge on the nucleus increases. The electrons are added to the same shell, so they are pulled closer to the nucleus. This causes the atomic radius to decrease and the ionisation energy to increase.

在同一周期中，质子数增加，因此原子核的正电荷增加。电子增加到同一壳层，因此它们被拉得更靠近原子核。这导致原子半径减小，电离能增大。

Down a group, the number of shells increases. The outer electrons are farther from the nucleus and are shielded by inner electrons, so the atom is larger and it is easier to lose an outer electron.

在同一族中，壳层数增加。外层电子离原子核更远，并且受到内层电子的屏蔽，因此原子更大，更容易失去外层电子。

These trends help predict the physical and chemical properties of elements. For example, the reactivity of alkali metals increases down the group because the outer electron is more easily lost, while the reactivity of halogens decreases down the group because it becomes harder to gain an electron.

这些趋势有助于预测元素的物理和化学性质。例如，碱金属的活性向下增强，因为外层电子更容易失去；而卤素的活性向下减弱，因为获得电子变得更加困难。

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Atomic Structure & The Periodic Table | 原子结构与元素周期表