AQA AS Chemistry

Revision Notes

3.1.2 Types of Formulae

Types of Formulae

  • The general formula is a formula that represents a homologous series of compounds using letters and numbers
    • Eg. the general formula of alkanes is CnH2n+2
    • A homologous series is a group of organic compounds that have the same functional group, the same general formula and the same chemical properties
  • The structural formula is a formula that shows how the atoms are bonded to each carbon atom in a molecule
  • The displayed formula is a 2D representation of an organic molecule showing all its atoms (by their symbols) and their bonds (by single, double or triple bonds)
  • The skeletal formula is a simplified displayed formula with all the carbon and hydrogen (C-H) bonds removed

Overview of the Formulae of Organic Compounds Table

 

Worked Example

Drawing skeletal formulae of molecules

Draw the skeletal formula of the following molecules:

  1. CH3(CH2)3OH
  2. (CH3)2CHCH2OH
  3. CH3CH2OCH2CH3

Answer:

An Introduction to AS Level Organic Chemistry Answer Worked example - Drawing skeletal formulae of molecules, downloadable AS & A Level Chemistry revision notes

Worked Example

Drawing displayed formulae of molecules

Draw the displayed formula of the following molecules:

 

Answer

An Introduction to AS Level Organic Chemistry Answer Worked example - Drawing displayed formulae of molecules, downloadable AS & A Level Chemistry revision notes

Molecular & Empirical Formulae

  • The molecular formula shows the number and type of each atom in a molecule
    • Eg. the molecular formula of ethanoic acid is C2H4O2
  • The empirical formula shows the simplest whole number ratio of the elements present in one molecule of the compound
    • Eg. the empirical formula of ethanoic acid is CH2O

Worked Example

Deducing molecular & empirical formulae

Deduce the molecular and empirical formula of the following compounds:

 

Answer

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