3.1.1Physical Chemistry
Functional Groups — AQA AS Chemistry Revision Notes & Topical Questions
5 min read 4 parts Lesson 64 of 102
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 4Key Terminology
Organic chemistry is the study of carbon compounds, and carbon forms so many because it can bond to itself in chains and rings.
Homologous series
- Homologous series A family of compounds with the same functional group and general formula, in which neighbouring members differ by CH₂.
Functional group
- Functional group The atom or group of atoms responsible for the characteristic chemical reactions of a compound.
Hydrocarbon
- Hydrocarbon A compound containing only hydrogen and carbon atoms, such as an alkane or alkene.
Saturated and unsaturated
- Saturated and unsaturated Saturated compounds contain only single bonds between carbons,
- while unsaturated compounds contain at least one C=C double bond.
Part 2 of 4Common Functional Groups
Common Functional Groups
General formulae
- General formulae Alkanes are CₙH₂ₙ₊₂, alkenes are CₙH₂ₙ, and alcohols are CₙH₂ₙ₊₁OH.
Shared properties
- Shared properties Members of a series show a gradual trend in physical properties, such as increasing boiling point with chain length.
Similar chemistry
- Similar chemistry All members of a series react in similar ways because they have the same functional group.
| Series | Functional group | Example |
|---|---|---|
| Alkane | C–C only | Ethane, C₂H₆ |
| Alkene | C=C | Ethene, C₂H₄ |
| Halogenoalkane | –Cl, –Br, –I | Bromoethane, C₂H₅Br |
| Alcohol | –OH | Ethanol, C₂H₅OH |
| Aldehyde | –CHO | Ethanal, CH₃CHO |
| Ketone | C=O between carbons | Propanone, CH₃COCH₃ |
| Carboxylic acid | –COOH | Ethanoic acid, CH₃COOH |
Part 3 of 4Classifying Structures
1
Aliphatic compounds have carbon chains that may be branched, while alicyclic compounds contain a ring of carbon atoms.
2
Aromatic compounds contain a benzene ring, which is a special delocalised six-carbon ring.
3
Primary, secondary and tertiary describe how many carbon atoms are attached to the carbon bearing the functional group.
4
A primary carbon is bonded to one other carbon, a secondary carbon to two, and a tertiary carbon to three.
5
Knowing the series and the type of carbon helps to predict which reactions a compound will undergo.
Part 4 of 4Exam Checklist & Tips
3.1.1 – Key Points for the Exam
- Homologous series A group of compounds with the same functional group and general formula, differing by CH₂ from one member to the next.
- Functional group The part of a molecule that determines its characteristic reactions.
- Saturated Containing only single carbon–carbon bonds.
- Aliphatic Containing carbon chains or non-aromatic rings, with no benzene ring.
Common Mistakes
- Saying members of a homologous series have identical physical properties; they show a gradual trend.
- Confusing the functional group of aldehydes (–CHO) with that of ketones (C=O within the chain).
- Describing a hydrocarbon as any compound containing carbon; it must contain only carbon and hydrogen.
- Forgetting that "differs by CH₂" refers to successive members of the series.
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