Edexcel A Level Chemistry:复习笔记3.1.1 Formulae of Organic Compounds

Formulae of Organic Compounds


  • Organic chemistry is the chemistry of carbon compounds
  • Carbon forms a vast number of compounds because it can form strong covalent bonds with itself
  • This enables it to form long chains of carbon atoms, and hence an almost infinite variety of carbon compounds are known
  • Hydrocarbons are compounds that are made up of carbon and hydrogen atoms ONLY


The diagram shows examples of hydrocarbons

Ethanol is NOT a hydrocarbon as the molecule also contains an oxygen atom and is not solely made up of carbon and hydrogen

  • Hydrocarbons can be placed into two categories
    • Saturated molecules containing single carbon-carbon bonds only
    • Unsaturated molecules containing double or triple carbon-carbon bonds
  • 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



Worked Example

Drawing displayed formulae of molecules
Draw the displayed formula of the following molecules:




  • 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: