Natures chemistry

• Homologous series

  A family of compounds with the same general formula and similar chemical properties
• Homologous series

  • Patterns are often seen in the physical properties of the members
  • Subsequent members show a general increase in their melting and boiling points
  • This is attributed to increasing strength of the intermolecular forces as the molecular size increases
• Hydrocarbons

  Compounds containing only hydrogen and carbon atoms
• Saturated compounds

  Compounds containing only single carbon-carbon bonds
• Unsaturated compounds

  Compounds containing at least one carbon-carbon double bond
• Distinguishing unsaturated from saturated compounds

  1. Using bromine solution

  2. Unsaturated compounds decolourise bromine solution quickly
• Structural formula


  A way to draw the structure of any molecule
• Isomers

  • Compounds with the same molecular formula but different structural formulae
  • May belong to different homologous series
  • Usually have different physical properties
• Alkanes


  • A homologous series of saturated hydrocarbons
  • Commonly used as fuels
  • Insoluble in water
  • Can be represented by the general formula CnH2n+2
• Cycloalkanes


  • A homologous series of saturated, cyclic hydrocarbons
  • Used as fuels and solvents
  • Insoluble in water
  • Can be represented by the general formula CnH2n
• Naming cycloalkanes

  Cycloalkanes (CnH2n) can be systematically named from structural formulae. Branched cycloalkanes are not required.
• Alkenes

  • A homologous series of unsaturated hydrocarbons
  • Used to make polymers and alcohols
  • Insoluble in water
  • Contain the C=C double bond functional group
  • Can be represented by the general formula CnH2n
• Writing and drawing alkenes

  Molecular formulae can be written and structural formulae can be drawn, from the systematic names of straight-chain and branched alkenes, containing no more than 8 carbons in the longest chain
• Addition reactions of alkenes

  1. With hydrogen forming alkanes (hydrogenation)

  2. With halogens forming dihaloalkanes

  3. With water forming alcohols (hydration)
• Alcohols


  • Used as fuels as they are highly flammable and burn with very clean flames
  • Often used as solvents
  • Methanol, ethanol and propanol are miscible with water, thereafter the solubility decreases as size increases
  • As alcohols increase in size their melting and boiling points increase due to the increasing strength of the intermolecular forces
  • Contain a hydroxyl functional group (-OH)
  • Can be represented by the general formula CnH2n+1OH
• Carboxylic acids


  • Used in the preparation of preservatives, soaps and medicines
  • Vinegar is a solution of ethanoic acid, with molecular formula CH3COOH
  • Vinegar is used in household cleaning products as it is a non-toxic acid so can be used safely in household situations
  • Methanoic, ethanoic, propanoic and butanoic acid are miscible in water, thereafter the solubility decreases as size increases
  • As carboxylic acids increase in size their melting and boiling points increase due to the increasing strength of the intermolecular forces
  • Can be identified by the carboxyl functional group (-COOH)
  • Can be represented by the general formula CnH2n+1COOH
• Carboxylic acid solutions


  • Have a pH less than 7
  • Like other acids, can react with metals, metal oxides, hydroxides and carbonates forming salts
  • Salts formed from straight-chain carboxylic acids containing no more than 8 carbons, can be named
• Exothermic

  A reaction or process that releases heat energy
• Endothermic

  A reaction or process that takes in heat energy
• Combustion

  A substance reacts with oxygen releasing energy
• Combustion of hydrocarbons and alcohols

  1. Hydrocarbons and alcohols burn in a plentiful supply of oxygen to produce carbon dioxide and water

  2. Equations can be written for the complete combustion of hydrocarbons and alcohols
• Fuels burn releasing different quantities of energy