11.1

Formulae, functional groups and nomenclature

Cambridge IGCSE Chemistry (0620)  · Unit 11: Organic chemistry  · 12 flashcards

Formulae, functional groups and nomenclature is topic 11.1 in the Cambridge IGCSE Chemistry (0620) syllabus , positioned in Unit 11 — Organic chemistry , alongside Alkanes, Alkenes and Alcohols.  In one line: Alkanes have the general formula CnH2n+2, where 'n' represents the number of carbon atoms in the molecule.

This topic is examined in Paper 1 (multiple-choice) and Papers 3/4 (theory), plus Paper 5 or Paper 6 (practical / alternative to practical). Past papers from 2022 to 2025 show this topic across undefined questions worth 131 marks (around 2.0% of all Chemistry marks in those years).

The deck below contains 12 flashcards — 9 definitions, 1 key concept and 2 identification cards — covering the precise wording mark schemes reward.  Use the 9 definition cards to lock down command-word answers (define, state), then move on to the concept and application cards to handle explain, describe and compare questions.

Key definition

The general formula for alkanes

Alkanes have the general formula CnH2n+2, where 'n' represents the number of carbon atoms in the molecule.

Example: butane (n=4) has the formula C4H10.

What the Cambridge 0620 syllabus says

Official 2026-2028 spec

These are the exact learning objectives Cambridge sets for this topic. Match the command word (Describe, Explain, State, etc.) in your answer to score full marks.

  1. Draw Draw and interpret the displayed formula of a molecule to show all the atoms and all the bonds
  2. Write Write and interpret general formulae of compounds in the same homologous series, limited to: (a) alkanes, CnH2n+2 (b) alkenes, CnH2n (c) alcohols, CnH2n+1OH (d) carboxylic acids, CnH2n+1COOH
  3. Identify Identify a functional group as an atom or group of atoms that determine the chemical properties of a homologous series
  4. State State that a structural formula is an unambiguous description of the way the atoms in a molecule are arranged, including CH2=CH2, CH3CH2OH, CH3COOCH3 Supplement
  5. Define Define structural isomers as compounds with the same molecular formula, but different structural formulae, including C4H10 as CH3CH2CH2CH3 and CH3CH(CH3)CH3 and C4H8 as CH3CH2CH=CH2 and CH3CH=CHCH3 Supplement
  6. State State that a homologous series is a family of similar compounds with similar chemical properties due to the presence of the same functional group
  7. State State that a saturated compound has molecules in which all carbon–carbon bonds are single bonds
  8. State State that an unsaturated compound has molecules in which one or more carbon- carbon bonds are not single bonds
  9. Describe Describe the general characteristics of a homologous series as: (a) having the same functional group (b) having the same general formula (c) differing from one member to the next by a –CH2– unit (d) displaying a trend in physical properties (e) sharing similar chemical properties Supplement
Definition Flip

What is the general formula for alkanes?

Answer Flip

Alkanes have the general formula CnH2n+2, where 'n' represents the number of carbon atoms in the molecule.

Example: butane (n=4) has the formula C4H10.
Definition Flip

What is the general formula for alkenes?

Answer Flip

Alkenes have the general formula CnH2n, where 'n' represents the number of carbon atoms in the molecule.

Example: ethene (n=2) has the formula C2H4.
Definition Flip

What is the general formula for alcohols?

Answer Flip

Alcohols have the general formula CnH2n+1OH, where 'n' represents the number of carbon atoms in the molecule.

Example: ethanol (n=2) has the formula C2H5OH.
Definition Flip

What is the general formula for carboxylic acids?

Answer Flip

Carboxylic acids have the general formula CnH2n+1COOH, where 'n' represents the number of carbon atoms in the molecule.

Example: ethanoic acid (n=1) has the formula CH3COOH.
Definition Flip

Define a functional group.

Answer Flip

A functional group is an atom or group of atoms within a molecule that is responsible for the characteristic chemical reactions of that molecule.

Example: the -OH group in alcohols.
Definition Flip

What are structural isomers?

Answer Flip

Structural isomers are compounds that have the same molecular formula but different structural formulae (different arrangements of atoms).

Example: butane (CH3CH2CH2CH3) and 2-methylpropane (CH3CH(CH3)CH3) both have the formula C4H10.
Definition Flip

What is a homologous series?

Answer Flip

A homologous series is a family of organic compounds with the same functional group, similar chemical properties, and a general formula, with each successive member differing by a -CH2- unit. Alkanes are an example.

Definition Flip

What defines a saturated compound?

Answer Flip

A saturated compound is one in which all carbon-carbon bonds are single bonds. Alkanes are saturated compounds (

Example: ethane, C2H6).
Definition Flip

What defines an unsaturated compound?

Answer Flip

An unsaturated compound is one in which one or more carbon-carbon bonds are not single bonds (i.e., they are double or triple bonds). Alkenes and alkynes are unsaturated (

Example: ethene, C2H4).
Key Concept Flip

List four general characteristics of a homologous series.

Answer Flip

Homologous series have the same functional group, the same general formula, differ by a –CH2– unit, display a trend in physical properties, and share similar chemical properties.

Key Concept Flip

Give the correct systematic name for Isopropyl alcohol.

Answer Flip

The correct systematic (IUPAC) name for isopropyl alcohol is propan-2-ol. This indicates that the -OH group is attached to the second carbon atom in a three-carbon chain.

Key Concept Flip

What reactants are required to produce ethyl propanoate?

Answer Flip

To produce ethyl propanoate you will need ethanol and propanoic acid and concentrated sulfuric acid as a catalyst.

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10.3 Carbon dioxide and methane 11.2 Alkanes

Key Questions: Formulae, functional groups and nomenclature

What is the general formula for alkanes?

Alkanes have the general formula CnH2n+2, where 'n' represents the number of carbon atoms in the molecule.

Example: butane (n=4) has the formula C4H10.
What is the general formula for alkenes?

Alkenes have the general formula CnH2n, where 'n' represents the number of carbon atoms in the molecule.

Example: ethene (n=2) has the formula C2H4.
What is the general formula for alcohols?

Alcohols have the general formula CnH2n+1OH, where 'n' represents the number of carbon atoms in the molecule.

Example: ethanol (n=2) has the formula C2H5OH.
What is the general formula for carboxylic acids?

Carboxylic acids have the general formula CnH2n+1COOH, where 'n' represents the number of carbon atoms in the molecule.

Example: ethanoic acid (n=1) has the formula CH3COOH.
Define a functional group.

A functional group is an atom or group of atoms within a molecule that is responsible for the characteristic chemical reactions of that molecule.

Example: the -OH group in alcohols.

Tips to avoid common mistakes in Formulae, functional groups and nomenclature

More topics in Unit 11 — Organic chemistry

Formulae, functional groups and nomenclature sits alongside these Chemistry decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.

11.2 Alkanes

13 flashcards
11.3 Alkenes

12 flashcards
11.4 Alcohols

11 flashcards
11.5 Carboxylic acids

12 flashcards
11.6 Esters

8 flashcards
11.7 Polymers

6 flashcards

Cambridge syllabus keywords to use in your answers

These are the official Cambridge 0620 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.

organic hydrocarbon carbon hydrogen homologous series functional group general formula molecular formula structural formula displayed formula nomenclature IUPAC prefix suffix

Key terms covered in this Formulae, functional groups and nomenclature deck

Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.

The general formula for alkanes
The general formula for alkenes
The general formula for alcohols
The general formula for carboxylic acids
A functional group
Structural isomers
Homologous series
What defines a saturated compound
What defines an unsaturated compound

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