Q1. [3] medium thorough-understanding
In an organic compound, all hydrogen atoms bonded to carbon are replaced one by one with chlorine atoms. (i) What is the term used for the –Cl group in organic chemistry? (ii) A chemist states that whether the compound has 2 carbon atoms or 10 carbon atoms in its chain, the chemical reactions it undergoes will remain largely the same. Explain why the chemist's statement is correct.
Generated by claude-sonnet-4-6 · 2026-06-26 01:10 · grounding rag
Model Answer
(i) The –Cl group is called a functional group (specifically, the halo/chloro functional group). It is also referred to as a heteroatom when considered as the replacing atom.
(ii) The chemist's statement is correct because chemical properties of a carbon compound are determined solely by its functional group, regardless of the length of the carbon chain. Whether the chloro (–Cl) group is attached to a 2-carbon or 10-carbon chain, it confers the same characteristic chemical properties to the compound. This is the basis of a homologous series — members differ in chain length but show similar chemical behaviour.
Source: Chapter 4, Sections 4.2.3 and 4.2.4
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Explanation
- For part (i), examiners accept "functional group" or "heteroatom"; both terms appear in the passage. Writing both is safest.
- For part (ii), the key phrase to use is: "chemical properties are determined solely by the functional group, regardless of the length of the carbon chain" — this is almost directly from the textbook and will earn full marks.
- Mentioning "homologous series" shows higher-order understanding and impresses examiners.
- Do not write about physical properties changing — that would contradict the chemist's statement and cost marks.