Chapter 22- Alkanes

  • Alkanes are hydrocarbons that contain only single covalent bonds between carbon atoms.
  • They have the general formula: CnH2n+2
  • A structural formula is the formula which shows how atoms are arranged in a molecule.
  • Alkanes are saturated hydrocarbons because they contain only single carbon-carbon bond.

 

ISOMERISM

  • Compounds that have the same molecular formula but different structural formula are isomers.
  • Branched alkyl groups are isomers of alkanes.

 

PROPERTIES OF ALKANES

  • As alkane molecules get bigger, the attractive forces become stronger.
  • Melting and boiling points, and density of alkanes increases as their molecular sizes increases.
  • Viscosity also increases as it becomes difficult to pour out bigger molecule chains.
  • The flammability decreases as the carbon chains become longer.
  • Complete combustion of alkanes produces carbon dioxide and water while incomplete combustion produces carbon monoxide and water.

CRACKING

  • Longer chains of alkanes are broken down to smaller chains of hydrocarbons which are more in demand. This process is cracking.

SUBSTITUTION REACTIONS

  • Alkanes are generally unreactive but they react with halogens.
  • One mole of chlorine substitutes one hydrogen atom. Another product of hydrogen chloride is formed.

 

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