Understanding the Periodic Table | 理解元素周期表

📚 Understanding the Periodic Table | 理解元素周期表

The Periodic Table is a systematic arrangement of all known chemical elements. In your IGCSE Edexcel Science course, you need to understand how it is organised, what information it provides, and how patterns in the table help predict the properties of elements. This revision guide breaks down the key ideas into clear sections with bilingual explanations to help you master the topic.

元素周期表是所有已知化学元素的有序排列。在IGCSE Edexcel科学课程中，你需要理解它的组织方式、它提供的信息，以及表中的规律如何帮助预测元素的性质。本复习指南将关键概念分为若干小节，并提供中英双语解释，帮助你掌握这一主题。

1. Atomic Structure | 原子结构

Every element is made of atoms. An atom consists of three subatomic particles: protons, neutrons and electrons. Protons have a positive charge (+1), electrons have a negative charge (−1), and neutrons have no charge. Protons and neutrons are found in the nucleus, while electrons move in shells around the nucleus.

每种元素都由原子构成。原子包含三种亚原子粒子：质子、中子和电子。质子带正电荷（+1），电子带负电荷（−1），中子不带电。质子和中子位于原子核内，而电子在核外的电子壳层中运动。

The atomic number (Z) equals the number of protons. It defines the element.
原子序数（Z）等于质子数，它决定了元素的种类。
The mass number (A) equals the total number of protons and neutrons.
质量数（A）等于质子数与中子数之和。

Number of neutrons = Mass number − Atomic number

中子数 = 质量数 − 原子序数

For example, carbon-12 has a mass number of 12 and an atomic number of 6, so it contains 6 protons, 6 electrons and 6 neutrons.

例如，碳-12的质量数为12，原子序数为6，因此它含有6个质子、6个电子和6个中子。

2. Elements, Compounds and Mixtures | 元素、化合物和混合物

An element is a pure substance made of only one type of atom. A compound is a substance formed when two or more elements chemically combine in a fixed ratio. A mixture contains two or more substances that are not chemically joined. The Periodic Table lists only elements, not compounds or mixtures.

元素是由一种原子组成的纯净物。化合物是两种或多种元素以固定比例化学结合形成的物质。混合物包含两种或多种没有化学结合的物质。元素周期表只列出元素，而不列出化合物或混合物。

Term	Example	Separated by
元素	氧气 O₂	化学方法不可分解
化合物	二氧化碳 CO₂	化学方法
混合物	空气	物理方法

3. Layout of the Periodic Table | 周期表的布局

The Periodic Table is arranged in rows called periods and columns called groups. Each box gives the element’s symbol, atomic number and relative atomic mass. The table is arranged in order of increasing atomic number.

元素周期表按行排列，横行为周期，纵列为族。每个方格给出元素的符号、原子序数和相对原子质量。周期表按原子序数递增的顺序排列。

There are about 118 elements. The first 94 occur naturally; the rest are synthetic. In the IGCSE course, you mainly need to know elements up to calcium (Z = 20), plus a few important transition metals.

周期表约有118种元素，前94种天然存在，其余为人工合成。在IGCSE课程中，你主要需要知道前20号元素（到钙），以及一些重要的过渡金属。

4. Periods and Groups | 周期和族

A period is a horizontal row. The period number tells you how many electron shells the elements have. For example, sodium (Na) is in period 3, so it has three electron shells. A group is a vertical column. The group number (for groups 1 to 8) tells you the number of outer-shell electrons of the elements in that group.

周期是横排，周期数告诉你该元素具有多少个电子壳层。例如，钠（Na）在第三周期，所以它有三个电子壳层。族是纵列，对于第1至8族，族数告诉你该族元素的外层电子数。

Group 1: alkali metals — 1 outer electron
第1族：碱金属 — 1个外层电子
Group 2: alkaline earth metals — 2 outer electrons
第2族：碱土金属 — 2个外层电子
Group 7: halogens — 7 outer electrons
第7族：卤素 — 7个外层电子
Group 8/0: noble gases — 8 outer electrons (helium has 2)
第8/0族：稀有气体 — 8个外层电子（氦为2）

5. Metals and Non-metals | 金属和非金属

The Periodic Table can be roughly divided into metals on the left and middle, and non-metals on the right. There is a zigzag line that separates them. Elements near the line, such as silicon (Si) and germanium (Ge), are metalloids with properties in between.

周期表大致可分为左侧和中间的金属，以及右侧的非金属。二者之间有一条阶梯线。靠近阶梯线的元素如硅（Si）和锗（Ge）是类金属，性质介于金属和非金属之间。

Property	Metal	Non-metal
光泽	有光泽	无光泽
导电性	良好	不良（石墨除外）
状态（室温）	固体（汞除外）	固、液、气
延展性	可延展、可锻造	脆

6. Electronic Configuration and Chemical Behaviour | 电子排布与化学行为

Electrons are arranged in shells around the nucleus. The first shell holds up to 2 electrons, the second and third shells each hold up to 8. The chemical properties of an element depend mainly on the number of electrons in its outermost shell. Elements in the same group have the same number of outer electrons, so they have similar chemical properties.

电子在原子核周围按壳层排列。第一壳层最多容纳2个电子，第二和第三壳层最多各容纳8个。元素的化学性质主要取决于最外层电子数。同一族的元素具有相同的外层电子数，因此化学性质相似。

Na (Z = 11): 2, 8, 1

Sodium has 1 outer electron, which it tends to lose to form a Na⁺ ion with a full outer shell. Chlorine (Z = 17) has 7 outer electrons, so it tends to gain 1 electron to form Cl⁻, achieving a stable octet.

钠有1个外层电子，倾向于失去该电子形成Na⁺离子，从而使外层达到全满。氯（Z = 17）有7个外层电子，倾向于获得1个电子形成Cl⁻，达到稳定的八电子结构。

7. Ions and Ionic Bonding | 离子与离子键

When metals react with non-metals, electrons are transferred from the metal to the non-metal. The metal forms a positive ion (cation), and the non-metal forms a negative ion (anion). The opposite charges attract, forming an ionic compound.

当金属与非金属反应时，电子从金属转移到非金属。金属形成正离子（阳离子），非金属形成负离子（阴离子）。异性电荷相互吸引，形成离子化合物。

For example, sodium chloride (NaCl) is formed when a sodium atom gives its outer electron to a chlorine atom:

例如，当钠原子将最外层电子给予氯原子时，形成氯化钠（NaCl）：

Na → Na⁺ + e⁻ Cl + e⁻ → Cl⁻ Na⁺ + Cl⁻ → NaCl

Ionic compounds have high melting points because of strong electrostatic attractions between ions. They conduct electricity when molten or dissolved in water, but not when solid.

离子化合物因离子间强烈的静电作用而具有高熔点。它们在熔融或溶于水时能导电，但在固态时不导电。

8. Covalent Bonding | 共价键

Non-metal atoms often share electrons to achieve a full outer shell. A shared pair of electrons is called a covalent bond. Covalent bonding occurs in molecules such as water (H₂O), carbon dioxide (CO₂) and methane (CH₄).

非金属原子常通过共享电子来达到满壳层。共享的一对电子称为共价键。共价键出现在水（H₂O）、二氧化碳（CO₂）和甲烷（CH₄）等分子中。

Water: H−O−H, with two single covalent bonds.
水：H−O−H，含有两个单共价键。
Carbon dioxide: O=C=O, with two double covalent bonds.
二氧化碳：O=C=O，含有两个双共价键。
Methane: four C−H single bonds arranged tetrahedrally.
甲烷：四个C−H单键，呈四面体排列。

Simple covalent substances have low melting points and do not conduct electricity. Giant covalent structures, such as diamond and graphite, have high melting points but only graphite conducts electricity.

简单共价物质熔点低，不导电。巨型共价结构，如金刚石和石墨，熔点高，但只有石墨导电。

9. Group 1: Alkali Metals | 第1族：碱金属

The alkali metals are lithium, sodium, potassium, rubidium, caesium and francium. They are soft, have low densities, and are very reactive. Reactivity increases down the group because the outer electron is further from the nucleus, so it is lost more easily.

碱金属包括锂、钠、钾、铷、铯和钫。它们质软、密度低、非常活泼。反应活性向下递增，因为外层电子离核更远，更容易失去。

They react with water to produce a hydroxide and hydrogen gas:

它们与水反应生成氢氧化物和氢气：

2Na + 2H₂O → 2NaOH + H₂

Sodium fizzes, melts into a ball and moves on the water surface. Potassium reacts even more violently with a lilac flame.

钠在水面上发出嘶嘶声、熔化成小球并四处游动。钾反应更加剧烈，产生淡紫色火焰。

10. Group 7: Halogens | 第7族：卤素

Halogens are non-metals with typical properties. They exist as diatomic molecules: F₂, Cl₂, Br₂, I₂. As you go down the group, they change from gas to liquid to solid, and their colour becomes darker. Reactivity decreases down the group because the atoms get larger and it becomes harder for them to gain an electron.

卤素是非金属，具有典型非金属性质。它们以双原子分子存在：F₂、Cl₂、Br₂、I₂。向下移动，状态从气体变为液体再到固体，颜色加深。反应活性向下递减，因为原子变大，更难获得电子。

More reactive halogens can displace less reactive halogens from their salt solutions:

较活泼的卤素可以从其盐溶液中置换出较不活泼的卤素：

Cl₂ + 2KBr → 2KCl + Br₂

Chlorine is more reactive than bromine, so it pushes bromine out of potassium bromide solution, turning it orange.

氯比溴活泼，所以氯能将溴从溴化钾溶液中置换出来，溶液变为橙色。

11. Group 8/0: Noble Gases | 第8/0族：稀有气体

The noble gases are helium, neon, argon, krypton, xenon and radon. They all have a full outer shell of electrons, so they are very stable and unreactive. They exist as monatomic gases and have very low boiling points.

稀有气体包括氦、氖、氩、氪、氙和氡。它们的最外层电子全满，因此非常稳定，不反应。它们以单原子气体存在，沸点极低。

Uses of noble gases include filling balloons (helium) and providing an inert atmosphere in welding or light bulbs (argon).

稀有气体的用途包括填充气球（氦）以及在焊接或灯泡中提供惰性气氛（氩）。

12. Development of the Periodic Table | 周期表的发展

Early chemists like Döbereiner and Newlands noticed patterns among elements, but it was Dmitri Mendeleev in 1869 who first arranged elements in a table based on atomic weight and left gaps for undiscovered elements. Later, Henry Moseley arranged the table by atomic number, providing the basis of the modern table we use today.

早期的化学家如德贝莱纳和纽兰兹注意到了元素间的规律，但直到1869年，门捷列夫才首次根据原子量排列元素表，并为未发现的元素留出空位。后来，亨利·莫塞莱按原子序数排列元素，为现代周期表奠定了基础。

Mendeleev predicted the properties of elements not yet discovered, such as germanium, which matched the gaps he left. This proved the power of the Periodic Table as a predictive tool.

门捷列夫预测了尚未发现元素的性质，例如锗，与他留下的空位完全吻合。这证明了周期表作为预测工具的强大力量。

13. Exam Tips and Common Mistakes | 考试技巧与常见错误

In the exam, remember to state both the number and the sign when writing ions. For example, write Mg²⁺, not Mg². Always specify that “number of electrons = number of protons for a neutral atom.” When comparing reactivity, explain it using electron loss or gain based on distance from the nucleus and the attraction of the nucleus.

在考试中，写离子时要同时注明数字和符号。例如，写Mg²⁺，而不是Mg²。始终说明“中性原子中电子数等于质子数”。比较反应活性时，要用电子得失、距核距离以及核对电子的吸引来解释。

Common mistakes: confusing period number with group number; thinking all atoms become ions; forgetting that helium has 2 outer electrons, not 8. Practice drawing dot-and-cross diagrams for ionic and covalent compounds.

常见错误：混淆周期数与族数；认为所有原子都会变成离子；忘记氦有2个外层电子而非8个。练习绘制离子化合物和共价化合物的点叉电子图。

Remember the group number for elements in groups 1 and 2 gives the number of outer electrons, and the period number gives the number of shells. For groups 3 to 7, the group number is not simply the number of outer electrons for all elements, but in the IGCSE course this pattern works for the main group elements.

记住：第1、2族的族数等于外层电子数，周期数等于电子壳层数。对于第3至7族，在IGCSE课程中，主族元素的族数也与最外层电子数有关，但需注意过渡金属例外。

Summary | 总结

The Periodic Table brings order to the elements. By understanding atomic structure, electron configurations and group trends, you can predict the chemical and physical properties of elements. Revise the definitions, key trends and example equations, and you will be well prepared for your Edexcel Science exam.

元素周期表将元素排列得井井有条。通过理解原子结构、电子排布和族的规律，你可以预测元素的化学和物理性质。复习定义、关键规律和示例方程式，你将在Edexcel科学考试中做好充分准备。

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Understanding the Periodic Table | 理解元素周期表