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1.8.2Unit 1. Structure, Bonding and Introduction to Organic Chemistry

Functional Groups and Homologous Series — IAL Edexcel Linear (Chemistry) Revision Notes & Topical Questions

5 min read 5 parts Lesson 28 of 36 Unit quiz

📚 IAL Edexcel Linear (Chemistry) Hub / Topical Revision
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Curriculum Equation Key معادلة تفاعل تكوين الإستر (الأسترة) - Esterification Reaction EquationFast Exam Solution
R-COOH + R2-OH ⇌ (conc. H₂SO₄) R-COO-R2 + H₂O
Word Equation & Conditions: حمض كربوكسيلي + كحول (في وجود حمض الكبريتيك المركز كعامل حفاز ونازع للماء) ⇌ إستر + ماء
Location & Specifications: الكيمياء العضوية للثانوية العامة والتحصيلي و Edexcel Chemistry.
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Part 1 of 5Key Definitions

Organising organic compounds into families makes it possible to predict their behaviour.

Functional group
  • Functional group An atom or group of atoms in a molecule that is responsible for its characteristic chemical reactions.
Homologous series
  • Homologous series A family of compounds with the same functional group and general formula, differing by one CH₂ unit from the next member.
Chemical properties
  • Chemical properties Members of a homologous series react in similar ways because they share the same functional group.
Physical properties
  • Physical properties Boiling points and other physical properties change gradually as the carbon chain gets longer.
Hydrocarbon
  • Hydrocarbon A compound containing only hydrogen and carbon atoms.

Part 2 of 5Common Functional Groups

Common Functional Groups
Alkane
  • Alkane Single C–C bonds only, general formula CₙH₂ₙ₊₂, and suffix -ane.
Alkene
  • Alkene A carbon-carbon double bond C=C, general formula CₙH₂ₙ, and suffix -ene.
Alcohol
  • Alcohol A hydroxyl group –OH on a carbon chain, general formula CₙH₂ₙ₊₁OH, and suffix -ol.
Halogenoalkane
  • Halogenoalkane A halogen atom replacing hydrogen, general formula CₙH₂ₙ₊₁X, with prefix chloro-, bromo- or iodo-.
Aldehyde and ketone
  • Aldehyde and ketone Both contain a C=O group;
    • an aldehyde has it at the end of the chain (–CHO) and a ketone within the chain.
Carboxylic acid
  • Carboxylic acid The –COOH group, with suffix -oic acid.
Homologous seriesFunctional groupExample
AlkaneC–CEthane, C₂H₆
AlkeneC=CEthene, C₂H₄
Alcohol–OHEthanol, C₂H₅OH
Halogenoalkane–BrBromoethane, C₂H₅Br

Part 3 of 5Types of Formula

1
The empirical formula gives the simplest whole number ratio of atoms, so ethane C₂H₆ has the empirical formula CH₃.
2
The molecular formula gives the actual number of each atom, such as C₄H₁₀ for butane.
3
The structural formula shows the arrangement of groups without every bond, for example CH₃CH₂CH₂CH₃.
4
The displayed formula shows every atom and every bond in the molecule.
5
The skeletal formula shows only the carbon backbone as lines, with functional groups labelled and hydrogens on carbon not shown.

Part 4 of 5General Formulae in Use

General Formulae in Use
Finding formula
  • Finding formula For an alkane with 6 carbons, 2n + 2 gives 14 hydrogens, so the formula is C₆H₁₄.
Checking unsaturation
  • Checking unsaturation Having fewer hydrogens than 2n + 2 shows the molecule contains a double bond or ring.
Saturated
  • Saturated A saturated compound has only single bonds between carbon atoms.
Aliphatic
  • Aliphatic Compounds with carbon in chains or non-aromatic rings are classed as aliphatic, whereas benzene-based compounds are aromatic.

Part 5 of 5Exam Checklist & Tips

1.8.2 – Key Points for the Exam

  • Functional group The group of atoms that gives an organic molecule its characteristic reactions.
  • Homologous series A family of organic compounds with the same functional group and general formula.
  • General formula An algebraic formula that applies to every member of a homologous series.
  • Saturated Containing only single carbon-carbon bonds.
  • Skeletal formula A simplified representation showing only the carbon skeleton and functional groups.

Common Mistakes

  • Saying the members of a homologous series have identical physical properties.
  • Writing C₂H₅OH as the formula of an alkane.
  • Forgetting that a ketone has C=O inside the chain and an aldehyde has it at the end.
  • Including hydrogens attached to carbon in a skeletal formula.

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