Covalent bond is a strong bond compared to Ionic Bonds but Ionic Compounds have higher melting and boiling points then covalent compounds. Why?
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2$\begingroup$ Maybe covalent bonds are stronger than ionic bonds. But ionic bonds are even stronger than that. $\endgroup$– Ivan NeretinMar 11, 2020 at 8:25
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$\begingroup$ You cannot generalise from the bonding type to whether a compound is high or low melting. There are ionic compounds that are liquid at room temperature and there are covalent compounds that have very, very high melting points (like graphite). $\endgroup$– matt_blackMar 13, 2020 at 13:22
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1 Answer
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When a substance is made of molecules, these molecules are made of atoms being strongly attached to one another. But a given molecule is not attached to its neighbor by strong bonds. On the contrary, they are attached by so-called van der Waals forces, which are rather weak. If you heat such a substance, the van der Waals forces are easy to destroy, and the substance melts easily. In the liquid, the covalent bonds are not modified.
When a substance is made of ions, the ionic bonds may not be as strong as covalent bonds. But they are stronger than van der Waals forces. This is why the ionic substances are melting at higher temperatures than substances made of pure covalent molecules.
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$\begingroup$ In a chemistry site one should be not afraid to say that ionic bonds per sé can be very strong, having energies exceeding that of covalent bonds. In principle and it in vacuum it can be. Nevertheless I simple and clear answer which I upvote. $\endgroup$ Mar 11, 2020 at 11:46
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$\begingroup$ chemistry.stackexchange.com/questions/21774/… and especially top answer therein. $\endgroup$ Mar 11, 2020 at 11:52