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

In this article, we will explore the key concepts of atomic structure and the periodic table as required for Edexcel IGCSE Science. You will learn about the particles that make up atoms, how the periodic table is organised, and how elements form bonds.

在这篇文章中，我们将探讨Edexcel IGCSE科学所要求的原子结构和元素周期表的核心概念。你将了解构成原子的微粒、元素周期表是如何组织的，以及元素如何形成化学键。

1. Inside the Atom | 原子内部

Every element is made of tiny particles called atoms. An atom consists of a central nucleus surrounded by electrons. The nucleus contains two types of particle: protons and neutrons.

每种元素都由称为原子的微小粒子组成。原子由一个位于中心的原子核和绕核运动的电子构成。原子核包含两类粒子：质子和中子。

Protons carry a positive charge, neutrons carry no charge, and electrons carry a negative charge. In a neutral atom, the number of electrons equals the number of protons.

质子带正电荷，中子不带电荷，电子带负电荷。在原子呈电中性时，电子数等于质子数。

2. Subatomic Particles | 亚原子粒子

The table below summarises the properties of the three subatomic particles that you need to memorise for the exam.

下表总结了三种亚原子粒子的性质，你需要在考试中牢记。

Particle	Charge	Relative mass
Proton	+1	1
Neutron	0	1
Electron	-1	1/1836

Electrons are so light that their mass is often ignored. The relative mass of a proton or neutron is approximately 1 atomic mass unit.

电子的质量非常小，通常可以忽略不计。质子或中子的相对质量约为1个原子质量单位。

3. Atomic Number and Mass Number | 原子序数与质量数

The atomic number (proton number) is the number of protons in the nucleus of an atom. It defines which element the atom belongs to. The mass number (nucleon number) is the total number of protons and neutrons.

原子序数（质子数）是原子核中的质子数目，它决定了该原子属于哪种元素。质量数（核子数）是质子和中子的总数。

Mass number = number of protons + number of neutrons

质量数 = 质子数 + 中子数

Therefore, the number of neutrons can be calculated by subtracting the atomic number from the mass number.

因此，中子的数量可以通过用质量数减去原子序数来计算。

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。也就是说，它们的原子序数相同而质量数不同。

For example, carbon-12 and carbon-14 are both isotopes of carbon. Carbon-12 has 6 protons and 6 neutrons, while carbon-14 has 6 protons and 8 neutrons.

例如，碳-12和碳-14都是碳的同位素。碳-12含有6个质子和6个中子，而碳-14含有6个质子和8个中子。

Isotopes have the same chemical properties because they have the same electron configuration. Their physical properties may differ slightly.

同位素具有相同的化学性质，因为它们具有相同的电子排布。它们的物理性质可能略有不同。

5. Electron Configuration | 电子排布

Electrons occupy shells (energy levels) around the nucleus. The first shell can hold up to 2 electrons, the second shell can hold up to 8 electrons, and the third shell can also hold up to 8 electrons for the first 20 elements.

电子占据原子核周围的壳层（能级）。第一壳层最多容纳2个电子，第二壳层最多容纳8个电子，对于前20号元素，第三壳层也可以容纳8个电子。

For example, a sodium atom has 11 electrons. Its electron configuration is 2,8,1. This shell arrangement is often written using numbers separated by commas.

例如，钠原子有11个电子，其电子排布为2,8,1。这种壳层排布通常用逗号分隔的数字来表示。

The electrons in the outer shell are called valence electrons and are responsible for the chemical behaviour of the atom.

最外层电子称为价电子，它决定了原子的化学行为。

6. The Periodic Table | 元素周期表

The periodic table arranges elements in order of increasing atomic number. Each horizontal row is called a period, and each vertical column is called a group.

元素周期表按照原子序数递增的顺序排列元素。每一横排行称为一个周期，每一纵列称为一个族。

The group number tells you how many electrons are in the outer shell. For example, elements in Group 1 have 1 outer-shell electron; elements in Group 2 have 2, and so on.

族序号告诉你最外层电子有多少。例如，第1族元素有1个最外层电子，第2族元素有2个，以此类推。

Metals are found on the left and middle of the table, while non-metals are on the right. Elements in the same group have similar chemical properties because they have the same number of outer electrons.

金属位于周期表的左侧和中部，非金属位于右侧。同一族的元素因为具有相同的最外层电子数而具有相似的化学性质。

7. Group 1: Alkali Metals | 第1族：碱金属

Group 1 elements include lithium, sodium and potassium. They are soft metals with low density, and they are stored in oil to prevent reaction with air.

第1族元素包括锂、钠和钾。它们是密度低的软金属，需储存在油中以防止与空气反应。

Alkali metals react with water to produce a metal hydroxide and hydrogen gas. For example, sodium reacts vigorously with water:

碱金属与水反应生成金属氢氧化物和氢气。例如，钠与水剧烈反应：

2Na + 2H₂O → 2NaOH + H₂

Going down the group, the metals become more reactive because the outer electron is farther from the nucleus and is lost more easily.

在元素周期表中向下移动，金属反应活性增强，因为最外层电子离原子核更远，更容易失去。

8. Group 7: Halogens | 第7族：卤素

Group 7 elements include fluorine, chlorine, bromine and iodine. They are non-metals with each atom needing to gain one electron to achieve a full outer shell.

第7族元素包括氟、氯、溴和碘。它们是非金属，每个原子需要得到1个电子以达到最外层满壳层。

Halogens exist as diatomic molecules, such as Cl₂ and Br₂. Their reactivity decreases as you go down the group, because the outer shell is further from the nucleus.

卤素以双原子分子形式存在，例如Cl₂和Br₂。其反应活性从上到下逐渐减弱，因为最外层电子壳层离原子核更远。

A more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt. For example, chlorine displaces bromine from potassium bromide solution.

一种更活泼的卤素可以从其盐的水溶液中置换出较不活泼的卤素。例如，氯可以将溴从溴化钾溶液中置换出来。

Cl₂ + 2KBr → 2KCl + Br₂

9. Group 0: Noble Gases | 第0族：稀有气体

Group 0 elements are helium, neon and argon. They are inert (unreactive) because their outer energy levels are already full.

第0族元素包括氦、氖和氩。它们是惰性的（不反应），因为最外层能级已经填满。

Noble gases exist as single atoms and are used in applications that require non-reactive environments. For example, argon is used in light bulbs and neon is used in advertising signs.

稀有气体以单原子形式存在，用于需要非反应环境的场合。例如，氩用于白炽灯泡，氖用于广告霓虹灯。

Because their outer shells are full, they do not easily gain or lose electrons, making them stable.

由于最外层壳层已满，它们不容易得失电子，因此非常稳定。

10. Ionic Bonding | 离子键

Ionic bonding occurs when a metal transfers electrons to a non-metal. The metal atoms lose electrons to become positively charged ions (cations), while non-metal atoms gain electrons to become negatively charged ions (anions).

当金属将电子转移给非金属时，就会形成离子键。金属原子失去电子变成带正电荷的离子（阳离子），而非金属原子获得电子变成带负电荷的离子（阴离子）。

The electrostatic attraction between oppositely charged ions holds the compound together. For example, sodium chloride is formed when sodium transfers one electron to chlorine.

带相反电荷离子之间的静电引力将所有离子结合在一起。例如，当钠将一个电子转移给氯时，就形成氯化钠。

Na· → Na⁺ + e⁻ | Cl· + e⁻ → Cl⁻

Ionic compounds have high melting points and conduct electricity when molten or in solution, but not when solid.

离子化合物熔点高，在熔融状态或水溶液中导电，固态不导电。

11. Covalent Bonding | 共价键

Covalent bonding occurs when non-metal atoms share pairs of electrons to achieve a full outer shell. A shared pair of electrons is called a single covalent bond.

共价键发生在非金属原子之间共享电子对以获得满壳层结构时。共享的一对电子称为单共价键。

For example, water contains two hydrogen atoms and one oxygen atom. Oxygen shares two electron pairs, one with each hydrogen atom.

例如，水分子包含两个氢原子和一个氧原子。氧原子共享两对电子，每对与一个氢原子共用。

Molecular compounds formed by covalent bonds have low melting points and do not conduct electricity because they have no free charged particles.

由共价键形成的分子化合物熔点低，不导电，因为它们没有自由移动的带电粒子。

12. Key Equations and Exam Tips | 关键方程与考试技巧

When writing equations for ion formation, remember that charges always balance. For the exam, you should be able to draw dot-and-cross diagrams for simple molecules such as H₂O, CH₄ and CO₂.

在写离子形成方程时，记住电荷必须守恒。考试中，你要能画出简单分子（如H₂O、CH₄和CO₂）的电子点叉示意图。

Always check the atomic number in the periodic table, and use the formula:

要经常查看周期表中的原子序数，并使用公式：

Number of electrons in an atom = atomic number

原子中电子数 = 原子序数

Practice writing electron configurations as numbers (e.g. 2,8,1) and matching them to groups in the periodic table. Good revision is the key to success.

练习用数字（如2,8,1）书写电子排布，并将其与周期表中的族对应。好的复习是成功的关键。

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