Non-metals are elements that do not show metallic characteristics like heat conductivity, electrical conductivity, malleability, e.t.c. They are generally less dense and are bonded with weak forces in between their compounds.
The weakness of non-metals is the chief reason why they generally tend to have low boiling point. Only the presence of impurities can cause an elevation in their boiling points.
Metals on the other hand are good heat conductors and they generally have a high boiling point.
