basic definitions

• Structural isomers

  Molecules with the same molecular formula but different structural formulae
• Homologous series

  same functional group but each successive member has an additional$-CH_2$
• Saturated hydrocarbons

  Contains only C-C covalent bonds
• Unsaturated hydrocarbons

  contains more than one carbon bond

  $C\equiv C$ or $C=$$C$
• Molecular formula

  The actual number of atoms of the elements in that compound
• Empirical formula

  The simplest whole number ratio of the atoms of each element in a compound
• Displayed formula

  Shows the relative position of each atom and all of the covalent bonds
• What does the displayed formula not show?

  The bond angles of$109.5^{\circ}$ and the arrangement of them (tetrahedral)
• Structural formula

  Shows how the atoms are arranged but not the bonds
• Skeletal formula

  Simplest possible way to represent the structure of an organic molecule. Carbon and hydrogen atoms are not shown, only covalent bonds between the carbons and any functional groups.
• General formula for alkane

  CnH2n+2
• Stereoisomers

  Molecules with the same structural formula but the atoms are arranged differently in space
• What are the covalent bonds called in an alkane?

  Sigma bonds
• How are sigma bonds formed?

  When electron orbitals from adjacent atoms directly overlap
• Key feature of sigma bonds

  They are fully rotational

  Relatively strong and take a lot of energy to break
• Why are alkanes non-polar molecules?

  Carbon and hydrogen have very similar electronegativity
• Properties of alkanes

  -Insoluble in water (no permanent dipoles)

  -Generally unreactive (Strong covalent bonds within the molecules)

  -Boiling point increases as the chain increases (More electrons, longer chains have greater surface area)(intermolecular forces are induced dipole dipole interactions, London forces are weak so are relatively easy to break for shorter chains)
• Propertied of branched chain alkanes

  Have lower boiling points than straight chain isomers

  Branches prevent alkane molecules from getting close together and London forces are reduced as they are stronger over short distances
• What are alkanes used for

  Fuel

  Starting materials for the production of organic molecules including pharmaceuticals
• Where are alkanes found

  Crude oil
• What is crude oil

  A fossil fuel made from the remains of plants and animals

  It is non-renewable
• Where is fractional distillation taken place?

  Fractionating columns
• Fractional distillation of alkanes

  • longer chain alkanes have a higher boiling point than shorter chain alkanes
  • If an alkane is taken as a gas and cool it to below its boiling point it will condense to a liquid