chapter 12

• alkanes have the general formula cnh2n+2

  alkanes contain one sigma bond that is caused by the head on overlap of two orbitals
• alkanes have a tetrahedral shape with a bond angle of 109.5 around each carbon atom
• boiling points increase as the carbon chain increases because there are stronger london forces due to greater surface area of contact which require more energy to overcome
• london forces are weak intermolecular forces that hold molecules together. the stronger the london forces, the greater the boiling point
• when branching increases, there are few surface area points of contact which causes weaker london forces, so boiling points decrease
• alkanes are unreactive because the C-C C-H bonds are strong and non polar
• in complete combustion there is a sufficient supply of oxygen, so carbon dioxide and water were formed

  in incomplete combustion there is a limited supply of oxygen so the products are water and carbon monoxide
• alkanes react with halogens in the presence of ultraviolet radiation to form haloalkanes in a mechanism called radical substitution
• step 1 initiation-

  the covalent bond is broken by homolytic fission to form two halogen radicals
• step 2 propagation-

  the first step forms a molecule of a hydrogen halogen

  the second step forms the haloalkane
• step 3 termination-

  the two radicals combine 3 times to stop the reaction