Alkanes

• Alkanes


  • Hydrocarbons with general formula of CnH(2n+2)
  • saturated hydrocarbons
  • contain only carbon-carbon single bonds
  • 1 carbon atom bonds with 4 other atoms
• Physical properties (alkanes)


  
  

  • simple discrete molecules
  • Low mp/bp since small amount of energy needed to overcome weak intermolecular foa
  • insoluble in water
  • soluble in organic solvents
  • Mp/bp increase down homologous series (more carbon lower in homologous series) foa increases, more energy needed to overcome foa
  • viscosity increases down the homologous series, molecular mass increases, foa stronger
  • Flammability decreases down the homologous series
• Chemical properties (alkanes)


  
  

  • generally unreactive as carbon-carbon single bonds and carbon-hydrogen bonds are very strong and hard to break
  • undergoes combustion (burning in oxygen)
  • Complete combustion : Alkanes burn in excess oxygen to form carbon dioxide and water
  • Incomplete combustion : alkanes burn in insufficient oxygen to form carbon monoxide and water. Soot may also be formed
  • As carbon atoms increase down the homologous series, alkane molecules burn with smokier or sootier flame
• Substitution Reaction


  • Alkanes undergo substitution reaction with chlorine gas or bromine gas in presence of ultraviolet light, which acts as a catalyst
  • Substitution reaction occurs when an atom or group of atoms is replaced with another atom or group of atoms
  • UV light breaks covalent bonds in chlorine/bromine molecule to form highly reactive chlorine/bromine atoms that can replace hydrogen atoms in alkane
  • only stops when all hydrogen atoms are replaced