Simple molecular substances are made up of molecules containing a few atoms joined together by covalent bonds such as H2, Cl2, O2, N2, CH4 (Methane), H2O and HCL
Substances containing covalent bonds usually have simple molecular strucutures. The atoms within the molecules are held together by strong covalent bonds but th forces of attraction between the molecules are weak. To melt or boil a simple molecular compounds, you only need to break these weak intermolecular forces and not the covalent bonds.This is because the molecules are easily parted from each other. As molecules get bigger, the strength of the intermolecular forces increase. They do not conduct electricity because they aren't charged and therre are no free elctrons