Chapter 12
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Sigma bond
The result of two overlapping orbitals Pair of electrons shared between bonding atoms
Alkanes shape
109.5 Tetrahedral shape
Why does more carbon atoms = ^ boiling point
More carbons Larger surfaces area of contact points between molecules More London forces Higher strength of attraction between alcane chains More heat need to overcome forces
Why does more branching = lower bp
More branching Less surface area of contact points between molecules Less London forces Lower strength of attraction between molecules Less energy needed to overcome forces
Complete combustion of alkanes
Alkane + oxygen –> carbon dioxide + water
Incomplete combustion of alkanes
Limited supply of oxygen Alkane + oxygen –> carbon monoxide / carbon (soot) + water
Alkanes undergo radical substitution (halogénation)
Presence of uv radiation Initiation propagation termination
Initiation of radical substitution
Halogen molecule absorbs uv radiation Undergoes homolytic fission 2 highly reactive radicals
Propagation radical substitution 2 steps
Step 1 Halogen reacts with hydrogen in h-c bond Producing an alkane radical and a hydrogen halide compound Step 2 Alkane radical reacts with another halogen molecule Producing an haloalkane and halogen radical
Termination - radical substitution
2 radicals collide Producing a molecule with all electron pairs The radicals are removed from the reaction mixture - stopping the reaction
What are the limitations of radical substitution and why does it happen
Produces a mixture of Of products, that may be unwanted and need to be filtered If there is too much halogen The hydrogen on wanted product with react with the halide forming an unwanted product To stop this make sure there is an excess of alkane so there is a greater chance of the halogen radical colliding with alkane