Functional groups, formulae and structural isomers
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The teaching part (2 min) is free to watch. A free account opens the whole lecture: 1 worked example, 3 practice questions, 3 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- Same atoms, different molecules
- Homologous series
- Functional groups and general formulas
Read the transcript of the teaching part
Last time
Before we start: last time, in Chiral centres and geometrical isomers, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
Same atoms, different molecules
Ethanol and dimethyl ether both have the formula C two H six O. One is a liquid you can drink, the other a gas used as a propellant. Atoms of the same elements, in the same numbers, arranged differently, give completely different substances. That is isomerism, and it is the key to organic chemistry.
Homologous series
A homologous series is a family of compounds with the same functional group, the same general formula, and successive members differing by CH two. Members show a gradation in physical properties, such as boiling point, and have similar chemical properties. The functional group is the atom or group of atoms that gives the compound its characteristic reactions.
Functional groups and general formulas
Alkanes: C n H two n plus two. Alkenes: C n H two n, with a C double bond C. Alcohols: C n H two n plus 1 OH, with the hydroxyl group. Halogenoalkanes: C n H two n plus 1 X. Aldehydes and ketones: C n H two n O, with a C double bond O. Carboxylic acids: C n H two n O two. Esters have the group COO between two carbon chains. Amines have NH two. Nitriles have C triple bond N. An aldehyde has the C double bond O at the end of the chain. A ketone has it in the middle.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: Counting all the isomers · Empirical and molecular formulas.
The whole chapter: An Introduction to AS Level Organic Chemistry, An Introduction to AS Level Organic Chemistry.
Chapter 13: Introduction to organic chemistry
- Functional groups, formulae and structural isomers 6 min
- Chiral centres and geometrical isomers 7 min
Also for A Level Chemistry 9701
Which topics come up most in A Level Chemistry 9701 past papers, counted from every paper since 2004: Paper 2 topic frequency, Paper 4 topic frequency.