Boiling and melting point of ionic and covalent compound?

Ionic compounds have higher boiling and melting points. It is because ionic compounds made up of ions. They are held together by strong electrostatic (ionic) bond. For example, in sodium chloride (NaCl), the Na+ ions are attracted to the Cl- ions. Because of the strong attraction forces, a huge amount of energy is needed to break down the bond, hence to melt the substance.

Covalent compounds have lower boiling and melting points. It is because the inter-molecular forces are very weak. Most of the attractions are between the atoms of the covalent molecules. For example, in an oxygen molecule, the two oxygen atoms share electrons. The forces between the atoms are strong, while the force between the molecules are very weak. Therefore, only a small amount of energy is needed to overcome these weak forces, hence to melt and to boil the substance.

Generally, covalent compound has a lower boiling and melting point than ionic conpound. Because the interaction btw all ion in ionic compound is ionic bond. And there are only wan der waal's force between covalent compound( simple molecular structure )e.g salt. However, when a covalent compound has a giant covalent structure, its boiling point and melting point will be extremely high. Because the interaction between each atom is covalent bone.

2007-03-15 02:01:26 補充：
van der waal

2007-03-15 02:02:00 補充：
van der waal

2007-03-18 02:27:16 補充：
It seems that all of the ionic compound have Giant ionic struture.I cannot ans you which one has a higher boiling point, as you know it will affect by different molecules.But I think giant covalent structure may have a higher boiling pt.Salt:melting pt about800(I remember)diamond:melting =3000