📚 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, as required for the Edexcel IGCSE Science specification. You will learn about subatomic particles, isotopes, electron arrangements, and how the periodic table is organised to reveal patterns in element properties.
本文涵盖 Edexcel IGCSE 科学大纲所要求的原子结构和元素周期表的核心概念。你将了解亚原子粒子、同位素、电子排布，以及元素周期表如何组织并揭示元素性质的规律。
1. Subatomic Particles | 亚原子粒子
Atoms are made of three fundamental particles: protons, neutrons and electrons. Protons carry a positive charge, neutrons are neutral, and electrons carry a negative charge. Protons and neutrons are found in the tiny central nucleus, while electrons occupy the space around it.
原子由三种基本粒子构成：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。质子和中子位于微小的原子核中，而电子占据核外空间。
proton charge = +1, electron charge = −1, neutron charge = 0
质子电荷 = +1，电子电荷 = −1，中子电荷 = 0
The relative masses of the particles are also important. A proton and a neutron each have a relative mass of 1, while an electron has a relative mass of only 1/1836. Therefore, almost all the mass of an atom is concentrated in the nucleus.
这些粒子的相对质量也很重要。一个质子或一个中子的相对质量为 1，而电子的相对质量仅约为 1/1836。因此，原子的几乎所有质量都集中在原子核中。
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 is. For a neutral atom, the number of electrons equals the number of protons.
原子序数（Z）是原子中的质子数。它决定了该原子属于哪种元素。对于中性原子，电子数等于质子数。
The mass number (A) is the total number of protons and neutrons in the nucleus. You can calculate the number of neutrons by subtracting the atomic number from the mass number:
质量数（A）是原子核中质子数与中子数的总和。你可以用质量数减去原子序数来计算出中子数：
neutron number = A − Z
中子数 = A − Z
For example, a carbon atom with mass number 12 and atomic number 6 has 6 protons and 6 neutrons.
例如，一个质量数为 12、原子序数为 6 的碳原子，有 6 个质子和 6 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.
同位素是同一元素的不同原子，它们具有相同的质子数，但中子数不同。
Since isotopes have the same number of protons and electrons, they show the same chemical properties. However, their physical properties, such as density and mass, may differ slightly.
由于同位素具有相同的质子数和电子数，它们表现出相同的化学性质。但它们的物理性质，如密度和质量，可能略有不同。
A common example is carbon-12 and carbon-14:
一个常见的例子是碳-12 和碳-14：
- Carbon-12: 6 protons, 6 neutrons
- Carbon-14: 6 protons, 8 neutrons
- 碳-12：6 个质子，6 个中子
- 碳-14：6 个质子，8 个中子
4. Electron Arrangement | 电子排布
Electrons are arranged in shells (energy levels) around the nucleus. The first shell can hold up to 2 electrons, the second and third shells can each hold up to 8 electrons.
电子围绕原子核排列在壳层（能级）中。第一层最多可容纳 2 个电子，第二层和第三层最多可各容纳 8 个电子。
The electron configuration of an atom is written by listing the number of electrons in each shell. For example, sodium has 11 electrons, so its arrangement is 2, 8, 1.
原子的电子排布通过列出每个壳层中的电子数来表示。例如，钠有 11 个电子，因此其排布为 2, 8, 1。
The outer-shell electrons are very important because they are involved in chemical reactions. Elements in the same group have the same number of outer-shell electrons, which explains why they have similar chemical properties.
最外层电子非常重要，因为它们参与化学反应。同一主族的元素具有相同的最外层电子数，这解释了它们为什么具有相似的化学性质。
5. The Layout of the Periodic Table | 元素周期表的布局
The periodic table arranges all known elements in order of increasing atomic number. Each element has a symbol, often derived from its English or Latin name.
元素周期表按原子序数递增的顺序排列所有已知元素。每种元素都有一个符号，通常来自其英文或拉丁文名称。
The table is divided into rows called periods and columns called groups. There are 18 groups in the standard periodic table, but for IGCSE you mainly need to know Groups 1, 7, and 0.
周期表被划分为行（称为周期）和列（称为族）。标准周期表有 18 个族，但 IGCSE 阶段主要需要了解第 1 族、第 7 族和第 0 族。
The period number = the number of occupied electron shells
周期数 = 已占据的电子壳层数
6. Periods and Groups | 周期和族
Going across a period from left to right, the atomic number increases and the number of outer-shell electrons increases by one each time. The properties change gradually from metallic to non-metallic.
在同一周期中从左到右，原子序数增加，最外层电子数每次增加 1。元素的性质逐渐从金属性变为非金属性。
Going down a group, the atoms gain an extra electron shell, so the atomic radius increases. This affects trends in properties such as reactivity and melting point.
在同一族中向下移动，原子增加一个电子壳层，因此原子半径增大。这会影响反应性和熔点等性质的递变规律。
For example, Group 1 elements get more reactive as you go down, while Group 7 elements get less reactive as you go down.
例如，第 1 族元素向下反应性增强，而第 7 族元素向下反应性减弱。
7. Metals and Non-metals | 金属与非金属
The periodic table can be roughly divided into metals and non-metals. Most elements are metals. Metals are found on the left and in the middle of the table, while non-metals are found on the right.
元素周期表大致可分为金属和非金属。大多数元素是金属。金属位于周期表的左侧和中部，非金属位于右侧。
Typical physical properties of metals include:
金属的典型物理性质包括：
- High melting and boiling points
- Good conductors of heat and electricity
- Malleable and ductile
- Usually shiny when freshly cut
- 熔点和沸点高
- 良好的热和电导体
- 具有延展性和可塑性
- 新切面通常有光泽
Non-metals generally show opposite properties, such as being brittle when solid and poor conductors of electricity.
非金属通常表现出相反的性质，如固态时较脆、导电性差。
8. Group 1: Alkali Metals | 第 1 族：碱金属
Group 1 elements are soft, shiny, highly reactive metals. They include lithium, sodium and potassium. They all have one electron in their outer shell, so they react in similar ways.
第 1 族元素是柔软、有光泽、高反应性的金属，包括锂、钠和钾。它们的最外层都有 1 个电子，因此反应方式相似。
When alkali metals react with water, they produce hydrogen gas and a solution of the metal hydroxide. For example:
当碱金属与水反应时，会产生氢气并生成金属氢氧化物溶液。例如：
2Na + 2H₂O → 2NaOH + H₂
As you go down the group, the atoms get larger and the outer electron is more easily lost, so reactivity increases.
随着族向下移动，原子变大，最外层电子更容易失去，因此反应性增强。
9. Group 7: Halogens | 第 7 族：卤素
Group 7 elements are non-metals called halogens. They include fluorine, chlorine, bromine and iodine. They have seven outer-shell electrons and need only one more electron to achieve a stable arrangement.
第 7 族元素是非金属，称为卤素，包括氟、氯、溴和碘。它们最外层有 7 个电子，只需再获得 1 个电子即可达到稳定结构。
Halogens exist as diatomic molecules, such as Cl₂, Br₂ and I₂. Their melting and boiling points increase as you go down the group.
卤素以双原子分子形式存在，如 Cl₂、Br₂ 和 I₂。随着族向下移动，它们的熔点和沸点升高。
Reactivity decreases down the group because the atoms become larger and it is harder to attract an extra electron.
反应性随族向下递减，因为原子变大，更难吸引额外的电子。
In displacement reactions, a more reactive halogen can displace a less reactive halogen from a solution of its salt. For example, chlorine can displace bromine from potassium bromide solution.
在置换反应中，较活泼的卤素能从其盐溶液中置换出较不活泼的卤素。例如，氯可以从溴化钾溶液中置换出溴。
10. Group 0: Noble Gases | 第 0 族：稀有气体
Group 0 elements are called noble gases. They include helium, neon and argon. They have full outer shells, so they are very stable and unreactive.
第 0 族元素称为稀有气体，包括氦、氖和氩。它们具有全满的最外层电子壳层，因此非常稳定，几乎不反应。
Noble gases are monatomic and they exist as individual atoms rather than molecules. They are used in lighting, welding and low-temperature applications.
稀有气体是单原子气体，以单个原子形式存在而非分子。它们用于照明、焊接和低温应用。
Because their electron arrangements are full, noble gases do not easily form ions or compounds. This is why they were once called ‘inert gases’.
由于电子排布饱和，稀有气体不易形成离子或化合物。这就是它们曾经被称为“惰性气体”的原因。
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