AQA AS Chemistry 4.2 Inorganic Chemistry | AQA AS化学4.2 无机化学

📚 AQA AS Chemistry 4.2 Inorganic Chemistry | AQA AS化学4.2 无机化学

This section of the AQA AS Chemistry scheme of work brings together three core inorganic topics: Periodicity, Group 2 metals, and Group 7 halogens. You will study patterns across Period 3, explain trends in terms of structure and bonding, and apply the same ideas to groups going down the periodic table. The key skills are describing trends, linking them to atomic structure, writing equations, and interpreting chemical tests.

AQA AS化学教学计划第4.2部分涵盖三大无机化学核心主题：元素周期律、第2族金属和第7族卤素。你将学习第3周期的规律，从结构与成键角度解释趋势，并将相同思路应用到周期表中各族自上而下的变化。本节的关键技能是描述趋势、将其与原子结构联系起来、书写化学方程式以及解释化学检验结果。

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1. Overview of Section 4.2 | 第4.2节总览

Inorganic chemistry in AS Level focuses on predictive patterns. Periodicity describes how properties of elements change across Period 3, while Group 2 and Group 7 show vertical trends down groups. You must be able to explain these trends using electron configuration, nuclear charge, shielding, atomic radius, and bonding type.

AS阶段的无机化学重点关注可预测的规律。元素周期律描述第3周期元素性质如何横向变化，而第2族和第7族则展示同一族自上而下的纵向趋势。你必须能够运用电子排布、核电荷、屏蔽效应、原子半径和成键类型来解释这些趋势。

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2. s, p and d Block Classification | s区、p区和d区分类

Elements are classified into blocks according to the orbital that receives the highest-energy electron. Group 1 and Group 2 elements are in the s block because their outer electrons occupy s orbitals. Groups 13 to 18 are in the p block because their outer electrons occupy p orbitals. Transition metals sit in the d block. At AS Level, the focus is mainly on the s and p blocks.

元素根据最高能量电子所进入的轨道类型划分为不同区。第1族和第2族元素位于s区，因为它们的价电子排布在s轨道中。第13族至第18族元素位于p区，因为它们的价电子排布在p轨道中。过渡金属位于d区。在AS阶段，重点主要放在s区和p区。

• Na: 1s² 2s² 2p⁶ 3s¹ → s block
• S: 1s² 2s² 2p⁶ 3s² 3p⁴ → p block

Na是s区元素，S是p区元素，两者的分类由最外层电子所在轨道决定。

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3. Period 3 Trend: Atomic Radius | 第3周期趋势：原子半径

Across Period 3 from sodium to chlorine, atomic radius decreases. The number of protons increases, so nuclear charge increases. Electrons are added to the same principal energy level, so shielding remains similar. The stronger attraction pulls the outer electrons closer to the nucleus, making atoms smaller.

从钠到氯，第3周期的原子半径逐渐减小。质子数增加，因此核电荷增加。电子添加到同一主能层，因此屏蔽效应基本不变。更强的核吸引力将外层电子拉得更靠近原子核，使原子半径减小。

Element	Na	Mg	Al	Si	P	S	Cl
Atomic radius	Decreases across Period 3

原子半径的变化是解释第3周期许多其他性质的基础，包括电离能和电负性。

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4. Period 3 Trend: First Ionisation Energy | 第3周期趋势：第一电离能

First ionisation energy generally increases across Period 3. Nuclear charge increases, atomic radius decreases, and outer electrons are held more strongly. However, there are two small drops: from Mg to Al and from P to S. The Mg-Al drop occurs because Al has its outer electron in a 3p orbital, which is slightly higher in energy and more shielded than the 3s orbital. The P-S drop occurs because sulfur has a paired electron in a 3p orbital, and electron-pair repulsion makes that electron easier to remove.

第3周期的第一电离能总体呈增大趋势。核电荷增加，原子半径减小，外层电子被更牢固地束缚。但存在两处小幅下降：从Mg到Al以及从P到S。Mg到Al下降是因为Al的最外层电子位于3p轨道，其能量略高且屏蔽稍强于3s轨道。P到S下降是因为硫的一个3p轨道中有一对成对电子，电子对之间的排斥作用使其中一个电子更容易失去。

Mg > Al (3s electron removed vs 3p electron removed)

P > S (half-filled 3p orbital vs paired 3p electrons)

这些“反常”下降是考试中的高频考点，必须用轨道排布和电子排斥来解释。

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5. Period 3 Melting Points and Structure | 第3周期熔点与结构

Melting points across Period 3 show a distinctive pattern. Sodium, magnesium, and aluminium are metals, and their melting points increase from Na to Al because metallic bonding becomes stronger: more electrons are delocalised and the ions become smaller and more charged. Silicon has a giant covalent structure, giving it the highest melting point in Period 3. Phosphorus, sulfur, and chlorine are simple molecular; their melting points are low, but S₈ melting point is higher than P₄ because S₈ molecules are larger and have more van der Waals forces. Argon is monatomic and has the lowest melting point.

第3周期熔点呈现出独特的模式。钠、镁、铝是金属，其熔点从Na到Al逐渐升高，因为金属键越来越强：离域电子增多，金属离子变小且所带电荷增大。硅具有巨大的共价结构，因此是第3周期中熔点最高的元素。磷、硫、氯为简单分子结构，熔点较低，但S₈的熔点高于P₄，因为S₈分子更大，具有更多的范德华力。氩为单原子分子，熔点最低。

Substance	Structure	Melting point trend
Na, Mg, Al	Metallic	Increases Na → Al
Si	Giant covalent	Very high
P₄, S₈, Cl₂	Simple molecular	Low; S₈ > P₄ > Cl₂
Ar	Monatomic	Lowest

在解释熔点时，务必先判断结构类型，再讨论粒子间作用力的大小。

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6. Group 2 Trends: Radius, Ionisation Energy, Melting Point | 第2族趋势：半径、电离能、熔点

Going down Group 2 from magnesium to barium, atomic radius increases because extra electron shells are added. First ionisation energy decreases because outer electrons are further from the nucleus and experience more shielding. Melting point generally decreases down the group because metallic bonding weakens: the ions become larger, so charge density decreases and the attraction between metal ions and delocalised electrons becomes weaker.

从镁到钡，第2族自上而下原子半径增大，因为增加了新的电子层。第一电离能降低，因为外层电子离核更远且屏蔽效应增强。熔点通常自上而下降低，因为金属键减弱：离子变大，电荷密度降低，金属离子与离域电子之间的吸引力减弱。

These trends help explain the increasing reactivity of Group 2 metals with water down the group.

这些趋势有助于解释第2族金属与水反应活性自上而下逐渐增强的原因。

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7. Group 2 Reactions with Water | 第2族与水的反应

Group 2 metals react with water to form a metal hydroxide and hydrogen gas. The reaction becomes more vigorous down the group. Magnesium reacts very slowly with cold water, calcium reacts steadily, strontium reacts quickly, and barium reacts vigorously. The general equation is:

第2族金属与水反应生成金属氢氧化物和氢气。自上而下反应越来越剧烈。镁与冷水反应非常缓慢，钙反应平稳，锶反应较快，钡反应剧烈。通式如下：

M + 2H₂O → M(OH)₂ + H₂ (M = Mg, Ca, Sr, Ba)

For example: Ca + 2H₂O → Ca(OH)₂ + H₂. The metal hydroxide is alkaline, so the solution turns red litmus blue. Solubility of Group 2 hydroxides increases down the group: Mg(OH)₂ is sparingly soluble, Ba(OH)₂ is much more soluble.

例如：Ca + 2H₂O → Ca(OH)₂ + H₂。生成的金属氢氧化物呈碱性，因此溶液使红色石蕊变蓝。第2族氢氧化物的溶解度自上而下增大：Mg(OH)₂微溶，Ba(OH)₂溶解度较大。

Reactivity increases down the group because ionisation energy decreases, so the metal loses its two outer electrons more easily.

反应活性自上而下增强是因为电离能降低，金属更容易失去两个外层电子。

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8. Group 2 Oxides and Industrial Uses | 第2族氧化物与工业用途

Group 2 metals burn in oxygen to form ionic oxides, for example:

第2族金属在氧气中燃烧生成离子型氧化物，例如：

2Mg + O₂ → 2MgO

Oxides react with water to form hydroxides. MgO reacts only slightly with water, while CaO reacts strongly to form Ca(OH)₂. The resulting solutions or suspensions are alkaline.

氧化物与水反应生成氢氧化物。MgO与水仅微弱反应，而CaO与水剧烈反应生成Ca(OH)₂。所得溶液或悬浊液呈碱性。

Three important uses are: magnesium is used to extract titanium by reducing TiCl₄;

Published by TutorHao | AS Revision Series | aleveler.com

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