GCSE Chemistry (AQA)

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General Formulae of Alkanes

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Organic chemistry Carbon compounds as fuels and feedstock

General Formulae of Alkanes

9:27 Hydrocarbons
Spec 4.7.1.1
Previous Crude Oil Fractions and Uses Next Combustion of Alkanes
  • Most hydrocarbons in crude oil are called alkanes.
  • Hydrocarbons are organic compounds consisting only of carbon and hydrogen atoms.
  • Alkanes form a homologous series, a family of compounds with similar chemical properties and the same general formula.
  • The general formula for alkanes is CnH2n+2, where n is the number of carbon atoms.
  • The first four alkanes are methane (CH4), ethane (C2H6), propane (C3H8), and butane (C4H10).
  • Each successive alkane has one more carbon atom and two more hydrogen atoms.
  • Alkanes can be represented by structural formulas, showing atoms and bonds.
  • Alkanes are made up of a chain of carbon atoms, each forming four bonds.
  • Methane has one carbon atom bonded to four hydrogens.
  • Ethane has two carbon atoms, each bonded to three hydrogens, with the last bond between the carbons.
  • Propane has three carbon atoms, with the middle carbon bonded to two hydrogens and the end carbons bonded to three hydrogens each.
  • Butane has four carbon atoms, with two end carbons bonded to three hydrogens and two middle carbons bonded to two hydrogens.
  • The pattern repeats for longer alkanes, with additional middle carbons bonded to two hydrogens.
  • The names of alkanes end in "ane," and the prefix indicates the number of carbon atoms.
  • Drawing structural formulas involves creating a carbon chain and adding hydrogens to satisfy the four-bond rule for carbon.
  • Example: For propane, the molecular formula is C3H8, and the structural formula involves a chain of three carbons with appropriate hydrogen bonds.

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