Why do some alkyl halides have higher boiling points as compared to others with a higher electronegativity?

I was under the impression that the high boiling points of alkyl halides was due to the dipole dipole forces in between molecules making them slightly polar. Yet why then does floromethane with such a high electronegativity difference have the lowest boiling point compared to other alkyl-methane groups? I know this is apparently due to their greater molecular mass' but how does that have relation to the topic? thanks