AS AQA Inorganic Chemistry: Periodicity, Group 2 and Group 7 | AS AQA 无机化学：周期性、第二族与第七族

📚 AS AQA Inorganic Chemistry: Periodicity, Group 2 and Group 7 | AS AQA 无机化学：周期性、第二族与第七族

Inorganic chemistry in the AS AQA specification, including OxfordAQA International A Level, is one of the most pattern-driven areas of the whole course. Success depends less on memorising isolated facts and more on mastering three core stories: the periodic trends across Period 3, the reactivity of Group 2 metals, and the redox behaviour of Group 7 halogens. Once you understand why these patterns exist, the exam questions become predictable and very manageable.

AQA（含牛津AQA国际版）的AS无机化学是整个课程中最强调规律的板块之一。拿高分并不靠零散背诵知识点，而在于掌握三条主线：第三周期的周期性规律、第二族金属的反应活性，以及第七族卤素的氧化还原行为。只要理解了这些规律背后的原因，大考中看似灵活的题目其实十分可预测，复习效率也会高得多。

1. The Big Picture | 整体框架

The AS inorganic syllabus has a tightly designed logic. Periodicity tells you how atomic properties change with proton number; Group 2 chemistry shows how an entire family of metals responds to the same reactions; Group 7 chemistry reveals how oxidising ability and reaction products change down a family of non-metals. All three threads depend on the same two ideas: nuclear charge and shielding.

AS无机部分的知识结构环环相扣。周期律讲的是原子性质随质子数的变化趋势；第二族展示一整族金属在同一类反应中的行为异同；第七族则揭示非金属一族氧化能力及反应产物的递变规律。三条主线其实都依赖两个核心概念：核电荷与屏蔽效应。

Exam questions rarely ask you simply to recite a fact. Instead, they will hand you an unfamiliar element or compound and ask you to predict its behaviour using the trends you have learned. This is why understanding the cause behind each trend is far more valuable than memorising a table of data.

大考很少要求你机械复述知识点。出题者往往会给你一个不熟悉的元素或化合物，要求你运用所学规律预测其行为。因此，理解趋势背后的成因远比背下一张数据表更有价值。

2. Atomic Radius Across Period 3 | 第三周期的原子半径

Across Period 3 from sodium to argon, the atomic radius decreases steadily. At each step, the nuclear charge increases by one proton, while the additional electron enters the same 3s or 3p sub-shell. The inner electrons provide a nearly constant shielding effect, so the growing nuclear charge pulls the outer electrons progressively closer to the nucleus.

第三周期从钠到氩，原子半径依次减小。每向右一步，核电荷增加一个质子，而新增电子进入相同的3s或3p亚层。内层电子提供的屏蔽效应几乎不变，不断增强的核电荷会把外层电子越拉越靠近原子核，因此半径收缩。

You should know the approximate values: Na 186 pm, Mg 160 pm, Al 143 pm, Si 117 pm, P 110 pm, S 104 pm, Cl 99 pm. Argon is usually discussed using its van der Waals radius

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