Question

if covelent bond have low boiling and melting point then why dimond have heigh melting and boiling points?? I will mark best answer as brainlist pakka​

Answer 1

Explanation:

Because covalent bonds don’t have low melting (Tm) and boiling points (Tb). Some examples:

Carbon, Tsublimation=3915 K (it doesn’t melt, it sublimates to gas)

Silicon, Tm=1414, Tb=3265

Tungsten (which is not entirely covalent but has a strong metallic part), Tm=3422 K, Tb=5555 K

What your textbook correctly states is that “Covalently bonded molecules have strong bonds within the molecule but intermolecular forces are low giving rise to lower melting and boiling point”. Let’s see what this means. Take water, H2OH2O. Two hydrogen atoms covalently bonded to one oxygen atom. This molecule is, by itself, stable and wouldn’t require any other bonds to complete the filling of its outer electronic shells so what’s solid water? And what about liquid water? Single molecules that are chemically stable liquify and solidify with weak bonds, such as Van der Waals forces. These are the weak links. These are easy to break and give rise to substances, such as water, such as ethylene, methane, etc that have low melting temperatures and boiling points.

If, on the other hand, you take a material made of a single atomic species (so the bond is intrinsically covalent, or metallic), you are not dealing with a stable covalent molecule in itself but with a covalent solid with only covalent bonds. These solids have no weak bonds to break but only strong, rigid, covalent bonds

Answer 2

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Diamond is very hard due to the strong covalent bonds and rigid tetrahedral 3d arrangement. It does not conduct electricity, as there are no electrons free to move and carry charge. It has a high melting point and boiling point as much energy is needed to break the many strong covalent bonds.