Explain why the three isomers have the same molecular mass but different boiling points?

Question

in terms of the type of bonding and/or the forces inbetween the molecules.

Pentane:- B.P= 36
Methylbutane:- B.P=28
Dimethylpropane:- B.P=9

Answer 1

The bonding is the same, but the attractive intermolecular (vdW) forces get progressively weaker. This is due to the lack of surface area overlap between neighbouring molecules if they have side branches - they can't pack together so well.