12.1 Properties of the alkanes

• Alkanes have the general formula CnH2n+2
• Alkanes are saturated hydrocarbons
• The C-C and C-H bonds in alkane molecules are sigma bonds
• Sigma bonds are formed from an overlap of orbitals directly between the bonding atoms
• Sigma bonds can freely rotate
• In alkane molecules, the carbon atoms form 4 bonded pairs of electrons, resulting in bond angles of 109.5 degrees
• As the carbon chain length increases, the boiling point increases

  • more electrons and more points of contact between molecules
  • increasing strength of induced dipole-dipole interactions
  • more energy needed to break the intermolecular forces
• As branching in isomers of alkanes increases, boiling point decreases

  • fewer points of contact between molecules
  • strength of induced dipole-dipole interactions decreases
  • less energy is needed to break the intermolecular forces
• Alkanes are non-polar molecules and do not dissolved in polar solvents like water