Aldehydes and Ketones for GCSE CCEA Chemistry | GCSE CCEA 化学：醛和酮 考点精讲

📚 Aldehydes and Ketones for GCSE CCEA Chemistry | GCSE CCEA 化学：醛和酮 考点精讲

Aldehydes and ketones are two important families of organic compounds that feature the carbonyl group (C=O). For GCSE CCEA Chemistry students, understanding their structures, naming, properties, and key reactions—especially oxidation and reduction—is essential. This guide breaks down everything you need to know about aldehydes and ketones, with clear explanations and comparison tables to help you succeed in your exam.

醛和酮是包含羰基（C=O）的两个重要有机化合物家族。对于学习 CCEA GCSE 化学的学生来说，理解它们的结构、命名、性质以及关键反应（尤其是氧化和还原）至关重要。本指南将详细讲解你需要掌握的关于醛和酮的所有知识，配有清晰的解释和对比表格，助你在考试中取得好成绩。

1. Introducing Aldehydes and Ketones | 醛和酮简介

Aldehydes and ketones both contain the carbonyl functional group, which consists of a carbon atom double-bonded to an oxygen atom (C=O). In aldehydes, the carbonyl carbon is always at the end of the carbon chain and is bonded to at least one hydrogen atom. In ketones, the carbonyl carbon is located in the middle of the carbon chain and is bonded to two other carbon atoms.

醛和酮都含有羰基官能团，它由一个碳原子与一个氧原子形成的双键（C=O）组成。在醛中，羰基碳总是在碳链的末端，并且至少与一个氢原子相连。而在酮中，羰基碳位于碳链中间，并与另外两个碳原子相连。

2. Functional Groups and General Formulae | 官能团与通式

The functional group for aldehydes is —CHO, often written as —C(H)=O. Their general molecular formula is CₙH₂ₙO (for n ≥ 1). The simplest aldehyde is methanal (HCHO). Ketones have the functional group —CO—, with a carbonyl group between two alkyl groups or aryl groups. The general formula for ketones is also CₙH₂ₙO, but n must be at least 3 (propanone, C₃H₆O, is the smallest ketone).

醛的官能团是 —CHO，通常写作 —C(H)=O。它们的一般分子通式为 CₙH₂ₙO（n ≥ 1）。最简单的醛是甲醛（HCHO）。酮的官能团是 —CO—，羰基位于两个烷基或芳基之间。酮的通式也是 CₙH₂ₙO，但 n 至少为 3（丙酮 C₃H₆O 是最小的酮）。

3. Naming Aldehydes and Ketones | 醛和酮的命名

IUPAC naming for aldehydes: Find the longest continuous carbon chain containing the –CHO group. Replace the final ‘-e’ of the corresponding alkane with ‘-al’. No number is needed for the aldehyde group when it is at the end of the chain. Examples: methanal (HCHO), ethanal (CH₃CHO), propanal (CH₃CH₂CHO). For ketones: Locate the longest chain with the carbonyl group, replace ‘-e’ with ‘-one’. Number the chain to give the carbonyl carbon the lowest possible number. Examples: propanone (CH₃COCH₃), butanone (CH₃COCH₂CH₃), pentan-2-one (CH₃COCH₂CH₂CH₃).

醛的 IUPAC 命名：找出包含 —CHO 的最长连续碳链，将对应烷烃末尾的“烷”字改为“醛”。由于醛基位于碳链末端，无需编号。例如：甲醛（HCHO）、乙醛（CH₃CHO）、丙醛（CH₃CH₂CHO）。酮的命名：找出带有羰基的最长碳链，将“烷”改为“酮”，并从靠近羰基的一端开始编号，使羰基碳的位次最小。例如：丙酮（CH₃COCH₃）、丁酮（CH₃COCH₂CH₃）、2-戊酮（CH₃COCH₂CH₂CH₃）。

4. Physical Properties | 物理性质

Aldehydes and ketones are polar molecules due to the electronegative oxygen in the carbonyl group. This gives them dipole-dipole interactions, but they cannot form hydrogen bonds with themselves (no O–H bond). As a result, their boiling points are higher than those of alkanes of similar molecular mass, but lower than those of corresponding alcohols and carboxylic acids. Short-chain aldehydes and ketones (up to about four carbons) are soluble in water because they can form hydrogen bonds with water molecules. Solubility decreases as the hydrocarbon chain length increases.

醛和酮由于羰基中存在电负性较强的氧原子而成为极性分子。这使它们具有偶极-偶极相互作用，但由于分子间没有 O–H 键，因此无法在自身间形成氢键。所以，它们的沸点高于相对分子质量相近的烷烃，但低于相应的醇和羧酸。短碳链的醛和酮（大约四个碳原子以内）能与水分子形成氢键，因而可溶于水。随着烃链增长，溶解度下降。

5. Oxidation of Aldehydes | 醛的氧化反应

Aldehydes can be easily oxidised

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