why iodine is a solid, bromine is a liquid and chlorine is gas at room temperature?

It has to do with intermolecular forces. I has the strongest, so it doesn't boil until 364degF; Br is next & boils at 137.8degF. Cl boils at -29.27degF.

Tags: intermolecular forcebriodinechlorinegas 
Thursday, February 02 2012
Source: http://education.jlab.org/itselemental/ele035.html