IGCSE Chemistry Notes Organic Chemistry / Formulae, functional groups and terminology

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Syllabus Objectives

IGCSE:Organic chemistry

Sub Topic:11.1 Formulae, functional groups and terminology

Syllabus Objectives:

CORE:

  • Draw and interpret the displayed formula of a molecule to show all the atoms and all the bonds
  • Write and interpret general formulae of compounds in the same homologous series, limited to:
  • (a) alkanes, Cn H2n+2
  • (b) alkenes, Cn H2n
  • (c) alcohols, Cn H2n+1OH
  • (d) carboxylic acids, Cn H2n+1COOH
  •  Identify a functional group as an atom or group of atoms that determine the chemical properties of a homologous series
  • State that a homologous series is a family of similar compounds with similar chemical properties due to the presence of the same functional group
  •  State that a saturated compound has molecules in which all carbon–carbon bonds are single bonds
  •  State that an unsaturated compound has molecules in which one or more carbon–carbon bonds are not single bonds

EXTENDED:

  • State that a structural formula is an unambiguous description of the way the atoms in a molecule are arranged, including CH2=CH2, CH3CH2OH, CH3COOCH3
  •  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
  • 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

Revision Notes

IGCSE Chemistry Notes  Organic Chemistry /Formulae, functional groups and terminology

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Core Objectives

  1. Displayed Formula of a Molecule:

    • Drawing and Interpretation:
      • Show all atoms and all bonds clearly.
      • Example: Ethane (C2H6) can be drawn as H3C-CH3 showing each hydrogen and the single bond between carbons.

  2. General Formulae of Compounds in Homologous Series:

    • Alkanes:
      • General Formula: CnH2n+2
      • Example: Methane (CH4), Ethane (C2H6)
    • Alkenes:
      • General Formula: CnH2n
      • Example: Ethene (C2H4), Propene (C3H6)
    • Alcohols:
      • General Formula: CnH2n+1OH
      • Example: Methanol (CH3OH), Ethanol (CH5OH)
    • Carboxylic Acids:
      • General Formula: CnH2n+1COOH
      • Example: Methanoic Acid (HCOOH), Ethanoic Acid (CH3COOH)

  3. Functional Group:

    • Definition: An atom or group of atoms that determine the chemical properties of a homologous series.
    • Examples: Hydroxyl group (-OH) in alcohols, Carboxyl group (-COOH) in carboxylic acids.

  4. Homologous Series:

    • Definition: A family of similar compounds with similar chemical properties due to the presence of the same functional group.

  5. Saturated and Unsaturated Compounds:

    • Saturated Compounds: Molecules with all carbon–carbon bonds as single bonds.
      • Example: Alkanes (e.g., Ethane C2H5)
    • Unsaturated Compounds: Molecules with one or more carbon–carbon bonds not being single bonds.
      • Example: Alkenes (e.g., Ethene C2H4)

Extended Objectives

  1. Structural Formula:

    • Definition: An unambiguous description of the arrangement of atoms in a molecule.
    • Examples:
      • Ethene (CH2=CH2)
      • Ethanol (CH3CH2OH)
      • Methyl ethanoate (CH3COOCH3)

  2. Structural Isomers:

    • Definition: Compounds with the same molecular formula but different structural formulae.
    • Examples:
      • Butane (C4H10): CH3CH2CH2CH3 and CH3CH(CH3)CH3
      • Butene (C4H8): CH3CH2CH=CH2 and CH3CH=CHCH3

  3. Characteristics of a Homologous Series:

    • Same Functional Group: All members have the same functional group.
    • Same General Formula: All members fit the same general formula.
    • Difference by –CH2– Unit: Each successive member differs by a –CH2– unit.
    • Trend in Physical Properties: There is a gradual change in physical properties (e.g., boiling points, melting points) within the series.
    • Similar Chemical Properties: Members have similar chemical reactions due to the same functional group.

 

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IGCSE Chemistry Revised Syllabus Notes[ 2023-2025 exams]

1-States of matter

2 Atoms, elements and compounds

3 Stoichiometry

4 Electrochemistry

5 Chemical energetics

6 Chemical reactions

7 Acids, bases and salts

8 The Periodic Table

9 Metals

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