Edexcel IGCSE Chemistry 复习笔记 4.1.1 Organic Compounds

Introduction

• Organic Chemistry is the scientific study of the structure, properties, and reactions of organic compounds. Organic compounds are those which contain carbon
• For conventional reasons metal carbonates, carbon dioxide and carbon monoxide are not included in organic compounds

Definition of a Hydrocarbon

• A compound that contains only hydrogen and carbon atoms

Representing Organic Molecules

• Organic compounds can be represented in a number of ways:
  • Empirical Formulae
  • Molecular Formulae
  • General Formulae
  • Structural Formulae
  • Condensed Structural Formulae

   

• The general formula shows a ratio of atoms in a family of compounds in terms of 'n' where n is a varying whole number
  • For example, the general formula of a molecule that belong to the alkane family is C_nH_2n+2

   

• The displayed formula shows the spatial arrangement of all the atoms and bonds in a molecule
• This is also known as the graphical formula.
  • For example:

   

• In a structural formulae enough information is shown to make the structure clear, but most of the actual covalent bonds are omitted
• Only important bonds are always shown, such as double and triple bonds
• Identical groups can be bracketed together
• Side groups are also shown using brackets
• Straight chain alkanes are shown as follows:

• Three important terms to know in this topic are homologous series, functional group and isomerism

Homologous Series

• This is a series or family of organic compounds that have similar features and chemical properties due to them having the same functional group
• All members of a homologous series have:
  • The same general formula
  • Same functional group
  • Similar chemical properties
  • Gradation in their physical properties
  • The difference in the molecular formula between one member and the next is CH₂

   

Functional Group

• Functional group: A group of atoms bonded in a specific arrangement that influences the properties of the homologous series
• Some examples are shown here

Structures and Names of Common Functional Groups

Isomerism

• Isomers are compounds that have the same molecular formula but different displayed formulae
  • Eg. propene and cyclopropane

   

Isomers of C₃H₆ show the same molecular formula but different structures. Isomers can show similar physical and chemical properties or if they have different functional groups, the properties can be different.

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