Question

do alkenes and alkynes have lower melting and boiling point than alkanes?why/why not?

Answer 1

Dear student,

The boiling point of alkene is slightly less than that of corresponding alkane since alkene has two electrons less than alkane.
The intermolecular force between between the alkane molecules and between the alkene molecules is van der Waals force.

The alkyne has higher melting point than alkane and alkene because of the triple bond. The triple bond shows the presence of the pi electrons which make it easier to induce dipole in the alkene and hence it give rise to stronger intermolecular force.

Regards