12.1 Properties Of Alkanes
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Alkane general formula
CnH2n+2
What are the bonds in alkanes called?
Sigma bonds
What is a sigma bond?
A head on overlap of orbitals
Shape and angle around a carbon atom in alkanes
Tetrahedral arrangement Bond angle of 109.5
Rotation around a sigma bond
Free rotation
Why can alkanes be separated using fractional distillation?
Boiling points of the alkanes are different BP increases as chain length increases
Why do longer chains have higher boiling points?
As chain length increases, surface area increases There is greater surface contact within the molecule Greater London forces so more energy is required to overcome these
Effect of branching on boiling point
Branched isomers have lower boiling points More branching - fewer surface points of contact between molecules of the branched alkanes Fewer London forces Branching also prevents them packing close together, so there are fewer intermolecular forces