Alkanes

• Carbon


  Forms more compounds than all other elements combined because it has certain properties
• Carbon


  • Has four valence electrons
  • Can potentially form covalent bonds with four different atoms
• Covalent bonds


  Can be a combination of single, double or triple bonds
• Because of the ability to form covalent bonds, carbon can bond to itself to form molecules of varied length and shape</b>
• Carbon-based molecules are all around you - caffeine, petrol, pesticides, plant and artificial flavours are all carbon-based compounds
• Crude oil


  Produced by the effects of heat and pressure on dead animals, plants and microorganisms trapped in the Earth's crust and buried beneath sediment formed over millions of years
• Organic chemistry


  The branch of chemistry that studies the chemistry of carbon compounds
• The amount of carbon on Earth is essentially fixed, with most of the carbon atoms having been here for billions of years
• Origin of crude oil


  1. Prehistoric marine microorganisms, such as bacteria and plankton, died and were buried by sands millions of years ago

  2. The organic material was affected by high temperatures and pressures, causing the oils and fats to be converted into hydrocarbons

  3. This mixture of hydrocarbons is crude oil
• Crude oil has a low density, which means it could migrate upwards through the Earth's crust, where it often became trapped beneath impervious rock
• Accumulation of oil and gas under the rock creates an oil field
• Fractional distillation of crude oil


  1. Crude oil is transported from oil fields to refineries

  2. It undergoes fractional distillation in a fractionating tower

  3. The crude oil is separated into its various components, or fractions

  4. Each fraction is made up of a range of hydrocarbons with similar boiling points and hence molecular masses

  5. The components of crude oil that are obtained by fractional distillation are used for a wide range of purposes
• Cracking


  1. Heavier fractions undergo a process called cracking

  2. This process breaks the larger hydrocarbon molecules into smaller ones

  3. The smaller molecules and especially those with carbon-carbon double bonds (called alkenes) are needed by the petrochemical industry
• Hydrocarbons


  Composed only of carbon and hydrogen
• Methane


  The simplest hydrocarbon, with one carbon atom covalently bonded with four hydrogen atoms to form a molecule with the formula CH4
• Alkanes


  Hydrocarbons that contain only single bonds, with all the carbon-carbon bonds being single covalent bonds
• Alkanes


  • Each member of the alkane series differs from the previous member by a -CH2- unit
  • Members of the same homologous series have similar structure, a pattern to their physical properties, similar chemical properties, and the same general formula
• Non-polar


  Alkanes have only weak forces between the molecules because they are non-polar
• As the number of carbons and the size of the alkane molecules increase, the strength of the intermolecular forces increases, so the melting and boiling points of the alkanes increase
• Stem names for molecules with 1-10 carbon atoms

  • meth-
  • eth-
  • prop-
  • but-
  • pent-
  • hex-
  • hept-
  • oct-
  • non-
  • dec-
• Alkanes


  Named by adding -ane after the stem name, e.g. octane
• Molecular formula of alkanes


  C_nH_2n+2, where n is the number of carbon atoms
• Ways to represent alkanes


  • Molecular formula
  • Lewis structure diagram (electron dot diagram)
  • Condensed structural formula
  • Structural formula
• Structural isomers are compounds with the same molecular formula but different arrangements of atoms
• Alkyl groups


  Side groups with one less hydrogen atom than the corresponding alkane, e.g. methyl (-CH3), ethyl (-CH2CH3)
• Structural isomers have different physical and chemical properties, such as different melting and boiling points
• IUPAC naming system for alkanes


  1. Identify the longest unbranched carbon chain

  2. Number the carbon atoms from the end closest to the branch

  3. Name the side branches and main chain

  4. Combine all components to write the full name
• IUPAC names for alkanes

  • 3-methylpentane

  3,3-dimethylpentane

  2,3-dimethylbutane
• The position of branches or substituents is indicated by numbering the carbon atoms in the main chain, starting from the end closest to the branch, to give the lowest possible locants to the substituents.
• If there are branches or substituents in the alkane molecule, they are named using prefixes like "methyl" or "ethyl" based on the number of carbon atoms in the branch.
• Alkanes are named based on the number of carbon atoms in the longest continuous chain, with the suffix "-ane" indicating it is an alkane.
• The reaction between an alkene and bromine water produces a mixture of dibromoalkane and tribromomethylalkane.
• Addition reactions of alkenes involve breaking the C=C double bond and adding another atom/group across it.
• Alkenes have lower boiling points than alkanes due to their polar nature caused by the presence of the double bond.