The covalent compounds have low melting and boiling points.
There is a reason behind this phenomenon.
In case of covalent compounds the molecules are non-polar and even if there is a polarity in the molecule, that is also just for a moment. Thus each molecule exists as a discrete particle which do not have affinity for other molecules.
And the intermolecular forces in covalent compounds are very low thus very less energy is required to change the state from solid to liquid and from liquid to gas.
But in case of ionic compounds there are ions (atoms with positive and negative charges) which attract each other strongly. And due to this it exists as a 3 dimensional networking molecule. Due to higher intermolecular forces the melting and boiling points of Ionic compounds are higher.