By David Fowkes on Friday, 12 October 2018
Category: IGCSE Chemistry

4.1 - 4.7 Organic chemistry

Organic chemistry is concerned with the compounds of the element carbon. Here we introduce the basic principles of this huge topic. 

 4.1 - 4.3. Activity 1. Speaking Organically

Organic chemistry is concerned with the compounds of the element carbon. Carbon atoms can form four covalent bonds with a range of other elements. 

Carbon chains form longer molecules and branches create a greater complexity. 

Atoms of hydrogen, nitrogen and oxygen will bond readily with carbon atoms and can ultimately form the molecules of life including amino acids and proteins.

 4.1 - 4.3. Activity 2. Alkanes, Alkenes and other terms...

 Students should:

  • 4.1 know that a hydrocarbon is a compound of hydrogen and carbon only
  • 4.2 understand how to represent organic molecules using empirical, molecular, general, structural and displayed formulae
  • 4.3 know what is meant by the terms homologous series, functional group and isomerism

When carbon atoms bond they usually form 4 covalent bonds. Hydrogen atoms form one bond. Thus the simplest hydrocarbon molecule which can form is methane. This has the formula CH4 .

Watch both of the videos carefully pausing where instructed. Use the videos to answer the questions below:

 4.3 Activity 3. Isomers: Same atoms, different arrangements

​Isomers are two or more molecules which have the same atoms ( and therefore the same molecular formula) but a different arrangement of atoms. We need to use structural or displayed formulae to show the differences between isomers:

 4.3 Activity 4. Functional Groups

Ethanol has the molecular formula C2H6O.  The molecule contains the - OH functional group. This is shown by the semi structural formula ;C2H5OH and the fully structural formula CH3CH2OH


​ethanoic acid has the -COOH functional group

 4.4 Activity 5. It's in the name

butane : molecular formula C4H10

3D ball and spoke model 

 fully displayed formula ( straight chain)

methylpropane : molecular formula C4H10

3D ball and spoke model  

fully displayed formula ( branched chain) 

 Students should:

  • 4.4 understand how to name compounds relevant to this specification using the rules of International Union of Pure and Applied Chemistry (IUPAC) nomenclature

 Activity 6

 Students should:

  • 4.5 understand how to write the possible structural and displayed formulae of an organic molecule given its molecular formula