The Periodic Table: Patterns and Trends | 元素周期表：模式与趋势

📚 The Periodic Table: Patterns and Trends | 元素周期表：模式与趋势

The periodic table is more than a list of elements; it is a powerful tool that organises chemical behaviour into clear patterns. In your Edexcel IGCSE science course, understanding these patterns helps you predict reactions, bond types, and physical properties with confidence.

元素周期表不只是元素的清单，更是一件强大的工具，它将化学行为整理成清晰的规律。在爱德思 IGCSE 科学课程中，理解这些规律能帮助你自信地预测反应、键的类型和物理性质。

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1. The Structure of the Periodic Table | 元素周期表的结构

The table is arranged in order of increasing atomic number (proton number). Each element has a unique symbol, and its position reflects its electronic configuration.

周期表按照原子序数（质子数）递增的顺序排列。每种元素都有独特的符号，其位置反映了它的电子排布。

• Atomic number (Z) = number of protons in the nucleus.

  原子序数（Z）= 原子核中的质子数。

• Mass number (A) = protons + neutrons.

  质量数（A）= 质子数 + 中子数。

• Elements in the same group have the same number of outer electrons.

  同一族的元素具有相同数目的外层电子。

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2. Periods and Groups | 周期与族

A horizontal row is called a period. A vertical column is called a group. The group number often tells you how many outer electrons an atom has (for groups 1 and 2, and 5–7).

水平行称为周期，垂直列称为族。族序数通常告诉你原子有几个外层电子（对于第1、2族以及第5–7族）。

For example, sodium (Na) is in period 3, group 1. It has three electron shells and one outer electron.

例如，钠（Na）位于第3周期、第1族。它有3个电子层和1个外层电子。

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3. Metals and Non-Metals | 金属与非金属

The periodic table is divided by a diagonal staircase line from boron (B) to polonium (Po). Metals are on the left and below the line; non-metals are on the right and above the line.

周期表被一条从硼（B）到钋（Po）的阶梯状对角线划分。金属位于该线的左侧和下方；非金属位于右侧和上方。

Metals 金属	Non-metals 非金属
Shiny, malleable, good conductors 有光泽、可锻、导电性好	Dull, brittle, poor conductors 暗淡、脆、导电性差
Form basic oxides 形成碱性氧化物	Form acidic oxides 形成酸性氧化物

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4. Group 1: Alkali Metals | 第1族：碱金属

Group 1 elements (lithium, sodium, potassium, rubidium, caesium) are soft, reactive metals with one outer electron.

第1族元素（锂、钠、钾、铷、铯）是柔软的、反应性强的金属，具有一个外层电子。

They react with water to produce hydrogen gas and a hydroxide solution. For example:

它们与水反应产生氢气和碱溶液。例如：

2Na + 2H₂O → 2NaOH + H₂↑

Reactivity increases down the group because the outer electron is further from the nucleus and more easily lost.

从上到下反应性增强，因为外层电子离核更远，更容易失去。

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5. Group 7: Halogens | 第7族：卤素

Group 7 elements (fluorine, chlorine, bromine, iodine) are non-metals with seven outer electrons. They need one more electron to achieve a stable octet.

第7族元素（氟、氯、溴、碘）是具有七个外层电子的非金属。它们需要再获得一个电子以达到稳定的八电子结构。

They form ionic compounds with metals and covalent compounds with other non-metals. Reactivity decreases down the group:

它们与金属形成离子化合物，与其他非金属形成共价化合物。反应性从上到下减弱：

• Fluorine is the most reactive halogen.

  氟是最活泼的卤素。

• A more reactive halogen can displace a less reactive one from its salt solution: Cl₂ + 2KBr → 2KCl + Br₂.

  活动性更强的卤素可以从其盐溶液中置换出活动性较弱的卤素：Cl₂ + 2KBr → 2KCl + Br₂。

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6. Group 0: Noble Gases | 第0族：稀有气体

Group 0 elements (helium, neon, argon, krypton, xenon) are monatomic gases with full outer electron shells. They are very unreactive.

第0族元素（氦、氖、氩、氪、氙）是具有满电子层的单原子气体。它们非常不活泼。

Their boiling points increase down the group because the atoms get larger and the van der Waals forces become stronger.

它们的沸点从上到下升高，因为原子变大，范德华力变强。

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7. Trends in Atomic Radius | 原子半径的变化趋势

Atomic radius is the distance from the nucleus to the outermost electron. Across a period, atomic radius decreases because the nuclear charge increases and electrons are pulled closer.

原子半径指从原子核到最外层电子的距离。在同一周期中，原子半径减小，因为核电荷增加，电子被拉得更近。

Down a group, atomic radius increases because extra electron shells are added.

在同一族中，原子半径增大，因为增加了新的电子层。

Across period → radius decreases | 同一周期从左到右半径减小
Down group → radius increases | 同一族从上到下半径增大

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8. Trends in Electronegativity | 电负性的变化趋势

Electronegativity measures an atom’s attraction for bonding electrons. It increases across a period because nuclear charge rises and atomic radius shrinks.

电负性衡量原子对成键电子的吸引能力。它在同一周期中增大，因为核电荷增加且原子半径减小。

It decreases down a group because the outer electrons are further away and more shielded by inner electron shells.

它在同一族中减小，因为外层电子更远，被内层电子屏蔽更多。

For example, fluorine is the most electronegative element, while francium is the least.

例如，氟是电负性最强的元素，而钫是最弱的。

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9. Ionic and Covalent Bonding | 离子键与共价键

Metals on the left lose electrons to form positive ions. Non-metals on the right gain electrons to form negative ions. When a metal and a non-metal react, electrons are transferred – this creates ionic bonds.

左侧的金属失去电子形成阳离子，右侧的非金属获得电子形成阴离子。当金属与非金属反应时，电子发生转移——这就形成离子键。

Between non-metals, electrons are shared – this creates covalent bonds. For example, H₂O has two covalent bonds.

在非金属之间，电子被共享——这就形成共价键。例如，H₂O 有两个共价键。

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10. Predicting Reactions | 预测化学反应

Once you understand group trends, you can predict a family of compounds. For example, all Group 1 metals form oxides with the formula M₂O, where M is the metal.

一旦你理解了族的规律，就可以预测一系列化合物。例如，所有第1族金属都会形成化学式为 M₂O 的氧化物，其中M代表金属。

Similarly, all Group 7 elements form hydrogen halides: HF, HCl, HBr, HI. The bond strength decreases down the group.

类似地，所有第7族元素都能形成卤化氢：HF、HCl、HBr、HI。键的强度从上到下减弱。

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11. The History of the Periodic Table | 元素周期表的历史

Dmitri Mendeleev arranged elements in order of increasing atomic weight and left gaps for undiscovered elements. He predicted their properties, which later elements confirmed.

门捷列夫按照原子量递增顺序排列元素，并为未发现的元素留出空位。他预测了这些元素的性质，后来得到证实。

Today, the table is ordered by atomic number, not atomic weight, because isotopes cause anomalies in atomic weight sequences.

如今，周期表按原子序数排序，而不是原子量，因为同位素会导致原子量序列出现异常。

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12. Summary and Exam Tips | 总结与考试提示

In Edexcel IGCSE exams, you may be asked to describe group trends or identify an element from its position. Always link electronic configuration to group number and period number.

在爱德思 IGCSE 考试中，你可能会被要求描述族的趋势，或根据位置识别元素。始终将电子排布与族序数和周期数联系起来。

• Know the special names: Group 1 alkali metals, Group 7 halogens, Group 0 noble gases.

  记住特殊名称：第1族碱金属、第7族卤素、第0族稀有气体。

• Remember that ionic bonds involve transfer, covalent bonds involve sharing.

  记住离子键涉及转移，共价键涉及共享。

• Practise writing balanced equations for group reactions.

  练习书写族反应配平的化学方程式。

Master these patterns and you will turn periodicity from memorisation into understanding.

掌握这些规律，你就能把周期性从死记硬背转化为真正的理解。

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