📚 IGCSE WJEC Chemistry: The Periodic Table Exam Essentials | IGCSE WJEC 化学：元素周期表 考点精讲
The periodic table is the chemist’s most powerful tool, organising all known elements in a way that reveals patterns and predicts chemical behaviour. For IGCSE WJEC Chemistry, a strong grasp of the table’s structure, group trends, and the link between electron arrangement and reactivity is essential. This revision guide covers every key examination point, from the basics of periods and groups to the distinctive properties of Group 1, Group 7, Group 0 and the transition metals, and shows you how to apply that knowledge confidently in the exam.
元素周期表是化学家最强大的工具，它以一种揭示规律并预测化学行为的方式将所有已知元素组织在一起。对于 IGCSE WJEC 化学来说，扎实掌握周期表的结构、族内的递变规律以及电子排布与反应性之间的联系至关重要。这份复习指南涵盖了从周期与族的基础知识到第1族、第7族、第0族和过渡金属的独特性质的所有考试要点，并教你如何在考试中自信地应用这些知识。
1. Overview of the Periodic Table | 元素周期表概述
The modern periodic table arranges elements in order of increasing atomic number (number of protons). This arrangement places elements with similar chemical properties in the same vertical column, known as a group.
现代元素周期表按照原子序数（质子数）递增的顺序排列元素。这种排列方式使得化学性质相似的元素位于同一纵列，即族。
The table was originally developed by Mendeleev, who left gaps for undiscovered elements and predicted their properties. In the IGCSE WJEC specification, you are expected to know that the table is structured into periods (horizontal rows) and groups (vertical columns), and be able to use the table to deduce an element’s electron arrangement and likely reactivity.
周期表最初由门捷列夫提出，他为尚未发现的元素留下了空位并预言了它们的性质。在 IGCSE WJEC 考试大纲中，你需要知道周期表由周期（横行）和族（纵列）构成，并能够利用周期表推断元素的电子排布和可能的反应性。
Elements on the left side and in the centre of the table are typically metals, while those on the right side are non-metals. The staircase line that separates metals from non-metals is a key visual guide.
周期表左侧和中间的元素通常是金属，而右侧的元素则是非金属。分隔金属和非金属的阶梯线是一个重要的视觉指引。
2. Periods and Electron Shells | 周期与电子层
The period number of an element tells you the number of occupied electron shells in its atoms. For example, lithium (Li) is in Period 2, so its atoms have two occupied shells; sodium (Na) is in Period 3, so it has three occupied shells.
元素的周期数告诉你其原子中占据的电子层数。例如，锂 (Li) 位于第2周期，因此其原子有两个电子层；钠 (Na) 位于第3周期，所以有三个电子层。
Across a period from left to right, the number of outer-shell electrons increases by one each time, while the number of occupied shells stays the same. This gradual change in outer electrons leads to a trend from metallic to non-metallic character across a period.
在同一周期中，从左到右，最外层电子数逐一递增，而占据的电子层数保持不变。这种外层电子的逐步变化导致了同周期从左到右金属性到非金属性的递变。
Understanding this link is critical: the position of an element in the periodic table directly reflects its electronic configuration, which in turn governs the element’s chemical properties.
理解这种联系至关重要：元素在周期表中的位置直接反映了它的电子排布，而电子排布又决定了该元素的化学性质。
3. Groups and Valence Electrons | 族与价电子
The group number (for Groups 1–2 and 13–18) indicates the number of electrons in the outermost shell, known as valence electrons. For example, all Group 1 elements have one outer electron; all Group 7 elements have seven outer electrons.
族序数（对于第1–2族和第13–18族）表示最外层的电子数，即价电子数。例如，所有第1族元素最外层都有一个电子；所有第7族元素最外层都有七个电子。
Elements in the same group undergo similar chemical reactions because they have identical outer-electron configurations. This is why sodium and potassium, both in Group 1, react with water in a comparable way, although potassium reacts more vigorously.
同一族的元素因为具有相同的最外层电子排布，所以发生类似的化学反应。这就是为什么同属第1族的钠和钾与水反应的方式相似，尽管钾的反应更为剧烈。
In WJEC IGCSE exams, you may be asked to deduce the group and period of an element from its electron configuration, or to write the electron arrangement of an element given its position in the table (e.g. 2.8.1 for sodium).
在 WJEC IGCSE 考试中，你可能会被要求根据电子排布推断元素的族和周期，或者根据元素在表中的位置写出其电子排布（例如钠的电子排布为2.8.1）。
4. Distribution of Metals and Non-metals | 金属与非金属的分布
Metals are found on the left-hand side and in the centre of the periodic table, including the transition metals block. Non-metals are concentrated on the right-hand side, with a staircase boundary starting between boron and aluminium.
金属位于周期表的左侧和中间区域，包括过渡金属区域。非金属集中在右侧，以一条始于硼和铝之间的阶梯线为界。
Metals tend to lose electrons to form positive ions (cations), while non-metals tend to gain electrons to form negative ions (anions). This simple rule explains why metals and non-metals form ionic compounds when they react together.
金属倾向于失去电子形成阳离子（正离子），而非金属倾向于得到电子形成阴离子（负离子）。这条简单的规则解释了为什么当金属和非金属一起反应时，它们会形成离子化合物。
Elements near the staircase, such as silicon, are often metalloids (semi-metals) that show intermediate properties — a detail that sometimes appears in higher-tier WJEC questions.
靠近阶梯线的元素，例如硅，通常是准金属（半金属），表现出介于两者之间的性质——这一细节偶尔会出现在 WJEC 的高阶题目中。
5. Group 1: The Alkali Metals | 第1族：碱金属
Group 1 contains lithium (Li), sodium (Na), potassium (K), rubidium (Rb) and caesium (Cs). These are soft, silvery metals with low densities that can be cut with a knife. They all have one electron in their outer shell.
第1族包含锂 (Li)、钠 (Na)、钾 (K)、铷 (Rb) 和铯 (Cs)。它们都是质地柔软、可用刀切的银白色金属，密度较低。它们的最外层都有一个电子。
Alkali metals are stored under oil because they tarnish rapidly in air and react vigorously with oxygen and water. Their reaction with water produces a metal hydroxide and hydrogen gas.
碱金属需保存在油中，因为它们在空气中会迅速失去光泽，并与氧气和水剧烈反应。它们与水的反应生成金属氢氧化物和氢气。
A typical equation you must learn for WJEC is:
2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g)
Lithium reacts gently, sodium more vigorously, and potassium so violently that it ignites the hydrogen produced, burning with a lilac flame. Rubidium and caesium react even more explosively.
锂反应温和，钠较剧烈，而钾反应极其猛烈，会点燃生成的氢气，并产生淡紫色火焰。铷和铯的反应甚至更具爆炸性。
6. Reactivity and Trends in Group 1 | 碱金属的反应性与趋势
Reactivity in Group 1 increases as you go down the group. This is because the outer electron is progressively further from the nucleus, experiencing more shielding from inner shells and a weaker electrostatic attraction, making it easier to lose.
第1族的反应性随着族往下而增强。这是因为最外层电子离原子核越来越远，受到内层电子更多的屏蔽，静电吸引力减弱，因此更容易失去。
As you move down the group, melting and boiling points generally decrease, and density increases slightly. You will be expected to explain these trends in terms of atomic structure, not just recite them.
沿族往下，熔点和沸点通常降低，密度略微增加。你需要从原子结构的角度解释这些趋势，而不仅仅是背诵。
A common WJEC question asks you to compare the reaction of lithium, sodium and potassium with water, noting observations such as fizzing, melting into a ball, flame colour and movement on the water surface.
WJEC 考试中常见的题目会要求比较锂、钠和钾与水的反应，注意到如嘶嘶作响、熔成小球、火焰颜色以及在水面游动等实验现象。
All Group 1 compounds are white solids that dissolve in water to give colourless solutions. The metal ions give characteristic flame colours: lithium (crimson), sodium (yellow/orange) and potassium (lilac) — a key identification test.
所有第1族化合物都是白色固体，溶于水形成无色溶液。这些金属离子会产生特征焰色：锂（深红色）、钠（黄色/橙色）和钾（淡紫色）——这是一项重要的鉴定检验。
7. Group 7: The Halogens | 第7族：卤素
Group 7 consists of fluorine (F), chlorine (Cl), bromine (Br), iodine (I) and astatine (At). They all have seven electrons in their outer shell and typically gain one electron to form a halide ion with a 1– charge, e.g. Cl⁻.
第7族包含氟 (F)、氯 (Cl)、溴 (Br)、碘 (I) 和砹 (At)。它们最外层都有七个电子，通常得到一个电子形成带1–电荷的卤离子，如 Cl⁻。
At room temperature, the physical states and colours are distinctive: chlorine is a pale green gas, bromine a red-brown liquid, and iodine a grey-black solid that sublimes to a purple vapour. You need to know these details for WJEC practical-based questions.
在室温下，它们的物理状态和颜色各具特色：氯是淡绿色气体，溴是红棕色液体，碘是灰黑色固体且会升华成紫色蒸气。你需要掌握这些细节以应对 WJEC 的实验类题目。
Halogens exist as diatomic molecules (Cl₂, Br₂, I₂) and react with metals to form ionic halides, such as sodium chloride. The balanced equation is:
2Na(s) + Cl₂(g) → 2NaCl(s)
Halogens also undergo displacement reactions: a more reactive halogen can displace a less reactive halogen from its halide solution. For instance, chlorine displaces bromine from potassium bromide solution, turning the solution orange.
卤素之间还会发生置换反应：反应性更强的卤素能把较弱的卤素从其卤化物溶液中置换出来。例如，氯能把溴从溴化钾溶液中置换出来，使溶液变为橙色。
8. Reactivity and Trends in Group 7 | 卤素的反应性与趋势
In contrast to Group 1, reactivity in Group 7 decreases going down the group. Fluorine is the most reactive halogen, and astatine the least. This is because the outer shell is further from the nucleus, making the attraction for an incoming electron weaker.
与第1族相反，第7族的反应性从上到下逐渐减弱。氟是最活泼的卤素，砹最不活泼。这是因为外层的距离原子核越来越远，对获得电子的吸引力变弱。
Melting and boiling points increase down the group, reflecting stronger intermolecular forces between larger diatomic molecules. You should be able to explain why iodine is a solid while chlorine is a gas at room temperature.
熔点和沸点沿族往下升高，这反映出较大的双原子分子之间分子间作用力更强。你应当能够解释为什么在室温下碘是固体而氯是气体。
In the WJEC IGCSE exam, you may be shown a table of observations for displacement reactions and asked to deduce the order of reactivity. Always link the colour change to the production of the displaced halogen.
在 WJEC IGCSE 考试中，可能会给出一张置换反应的现象表格，要求你推断反应性顺序。务必将颜色变化与被置换出的卤素联系起来。
The halogens form acidic solutions and are toxic. Their halide ions can be identified by adding silver nitrate solution and observing precipitate colours: white for chloride, cream for bromide and yellow for iodide.
卤素形成酸性溶液且有毒。它们的卤离子可以通过加入硝酸银溶液并观察沉淀颜色来鉴定：氯化物为白色，溴化物为奶油色，碘化物为黄色。
9. Group 0: The Noble Gases | 第0族：惰性气体
Group 0 (also called Group 18) includes helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe) and radon (Rn). They all have full outer electron shells — two for helium, eight for the rest — giving them exceptional chemical inertness.
第0族（也称第18族）包括氦 (He)、氖 (Ne)、氩 (Ar)、氪 (Kr)、氙 (Xe) 和氡 (Rn)。它们都具有全满的最外层电子——氦为两个，其余为八个——这使得它们具有极强的化学惰性。
Because the atoms do not need to gain, lose or share electrons, noble gases exist as monatomic gases and are very unreactive. This stability explains why they are used in applications such as helium in balloons and argon in light bulbs.
由于这些原子不需要得到、失去或共享电子，惰性气体以单原子气体形式存在，且极不活泼。这种稳定性解释了它们为何被用于充气球（氦气）和灯泡填充（氩气）等领域。
WJEC questions often test your understanding that the lack of reactivity is due to the stable electron arrangement, not because the atoms are ‘tired’ or ‘weak’. A full outer shell is the key concept.
WJEC 题目经常考查你是否理解惰性原因在于稳定的电子排布，而非因为原子“累了”或“弱”。全满的最外层电子是关键概念。
Boiling points increase down the group, though they remain low. Helium has the lowest boiling point of any element, which makes it useful for cooling superconducting magnets in MRI scanners.
沸点沿族往下升高，但仍保持较低。氦是所有元素中沸点最低的，这使其可用于冷却 MRI 扫描仪中的超导磁体。
10. Transition Metals | 过渡金属
Transition metals are located in the central block of the periodic table, between Group 2 and Group 3. Common examples include iron (Fe), copper (Cu), zinc (Zn) and chromium (Cr). For WJEC IGCSE, you must contrast their properties with those of Group 1 metals.
过渡金属位于周期表中部，即第2族和第3族之间。常见的例子有铁 (Fe)、铜 (Cu)、锌 (Zn) 和铬 (Cr)。在 WJEC IGCSE 中，你需要将其性质与第1族金属进行对比。
Transition metals are harder, stronger, and have much higher melting points than alkali metals. They are less reactive: for instance, iron reacts slowly with air and water to rust, while sodium reacts instantly with water.
过渡金属比碱金属更硬、更强韧，熔点也高得多。它们的反应性较低：例如，铁与空气和水缓慢反应而生锈，而钠遇水即刻剧烈反应。
They form coloured compounds (e.g. copper(II) sulfate is blue, iron(II) compounds are pale green) and often have more than one stable oxidation state. Many transition metals and their oxides are important catalysts, such as iron in the Haber process and vanadium(V) oxide in the Contact process.
它们能生成有色化合物（如硫酸铜(II)为蓝色，铁(II)化合物为淡绿色），并往往具有不止一种稳定氧化态。许多过渡金属及其氧化物是重要的催化剂，例如哈伯法中的铁和接触法中的五氧化二钒。
Tip: in the exam, if asked for a use of a transition metal, do not give an erroneous answer such as ‘sodium is used for bridges’. Always remember that transition metals are the typical engineering metals.
提示：考试中如果问到过渡金属的用途，不要给出诸如“钠用于造桥”的错误答案。始终牢记，过渡金属才是典型的工程金属。
11. Predicting Properties Using the Periodic Table | 利用周期表预测化学行为
One of the most common WJEC exam skills is predicting the properties of an element based on its group and period. For example, if an unfamiliar element X lies below potassium in Group 1, you can predict it will be even softer, have a lower melting point and react more violently with water.
WJEC 考试中最常见的技能之一是根据元素所在的族和周期预测其性质。例如，如果某未知元素 X 位于第1族钾的下方，你可以预测它更软、熔点更低、与水反应更猛烈。
You can also predict the formula of compounds by applying group patterns. A Group 2 element will form a compound of the type MCl₂ when combined with chlorine, because it loses two electrons to achieve a stable electron arrangement.
你还可以通过应用族内的规律来预测化合物的化学式。第2族元素与氯结合时会形成 MCl₂ 型化合物，因为它失去两个电子以达到稳定电子排布。
The periodic table also allows you to compare atomic size. Atoms become larger down a group and smaller across a period (due to increasing nuclear charge pulling the electrons closer). This size trend influences reactivity.
周期表还可以让你比较原子大小。在同族中原子自上而下变大，在同周期中从左到右变小（因为核电荷增加将电子拉得更靠近原子核）。这种大小趋势影响着反应性。
Always justify your predictions using electron configuration and the idea of outer-shell attraction. A common mark in WJEC mark schemes is awarded for stating ‘the outer electron is further from the nucleus and is more shielded, so it is lost more easily’.
做出预测时一定要用电子排布和外层电子吸引力的概念来论证。WJEC 的评分标准中，常因说出“最外层电子离核更远且受到更多屏蔽，因此更容易失去”而得分。
12. Common Exam Questions and Tips | 常见题型与应试技巧
WJEC IGCSE questions on the Periodic Table often include completing tables of properties, writing word and symbol equations, and explaining trends. You must be precise with state symbols (s, l, g, aq) and charges on ions.
WJEC IGCSE 关于元素周期表的题目经常包括补全性质表格、书写文字与符号方程式，以及解释变化趋势。你必须精准使用状态符号 (s, l, g, aq) 和离子电荷。
A typical 3-mark question might ask: “Explain why potassium is more reactive than sodium.” The perfect answer links atomic structure: potassium atoms are larger, have the outer electron in a shell further from the nucleus, feel a weaker attractive force, and therefore lose the electron more readily.
一个典型的3分题目可能会问：“解释为什么钾比钠更活泼。”完美的答案要将原子结构联系起来：钾原子更大，最外层电子离核更远，受到的吸引力更弱，因此更容易失去电子。
When drawing diagrams of electron arrangements, always show the shells as circles and write the number of electrons in each shell. Label the nucleus and remember the 2.8.8.2 rule for the first 20 elements.
绘制电子排布示意图时，始终用圆圈表示电子层，并在每层写上电子数。标注原子核，并记住前20号元素的2.8.8.2排布规则。
Finally, practise past paper questions on displacement, flame tests and noble gas uses. Be prepared to write a balanced equation and state the colour change observed. With a thorough understanding of the periodic table, you can tackle any WJEC IGCSE Chemistry question with confidence.
最后，要大量练习关于置换反应、焰色反应和惰性气体用途的历年真题。准备好书写配平方程式并描述观察到的颜色变化。透彻理解元素周期表，你就能充满信心地应对任何 WJEC IGCSE 化学试题。
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