Which Bond is Stronger: Metallic or Covalent?

[photon79]

which is the strongest of all the chemical bonds? metallic or covalent?

 

[Bladibla]

Metallic, or ionic.

 

[photon79]

but the strong diamond is foemed by covalent bond!

 

[Facial]

I really don't know, and that's a pretty darn good question. I'd like to know myself from some of the experts.

You can probably tell the bond strength roughly by the melting temperature of the solid, which is where interatomic interactions partially break loose. In this case, tungsten is the solid with the highest melting temperature (at STP) of any element.

But if you take a look at carbon, which essentially is a covalent network solid, it sublimes at a temperature just above tungsten's melting point. This suggests that covalent bonds can be quite tough as well.

The highest melting of any ionic solid that I have encountered is MgO, which liquefies at just over 2800 C. Pretty impressive.

 

[ZapperZ]

The crystal structure can determine the bond length, and thus, the "hardness". For example, if you look at graphite, the c-axis bonds are very long when compared to the in-plane bonds. So graphite appears to be "soft" simply because one can "shave off" sheets of graphite structure.

On the other hand, the same carbon atoms when arranged in a hexagonal closed-pack, will have extremely short bond length. This produces a stronger material, even when the atom and the type of bonding are the same as graphite.

Zz.

 

[fasterthanjoao]

They overlap.

Bond energy strengths can be taken roughly as:

Ionic 5ev (per bond) {with a boiling dissociation >1000K}
covalent 1-5ev (per bond) {boiling dissociation >1000K for non-molecular solids}
metallic 1-2ev (per atom) {boiling dissociation 1000K}

----
intermolecular: hydrogen 0.5ev (per bond)
van der waals 0.1 per atom (or formula unit)

 

[fargoth]

melting temperature isn't a good indicator for bond energy - the boiling point is a better measure.

it seems from what i found so far that Rhenium (with 5627.0 °C boiling temperature) is the matter with the highest bonding energy.
after that you get Tungsten (with 5555°C boiling temperature).


(note that at high temperatures like these the values arent accurate, litterature gives more then one value here for the boiling points, but I am pretty sure that Rhenium has higher boiling temperature...)

while Carbon boils at 4827°C


anyway, i don't know how to calculate these values...
it'll be interesting if anyone around here knew it.

 

[fargoth]

They overlap.

Bond energy strengths can be taken roughly as:

Ionic 5ev (per bond) {with a boiling dissociation >1000K}
covalent 1-5ev (per bond) {boiling dissociation >1000K for non-molecular solids}
metallic 1-2ev (per atom) {boiling dissociation 1000K}

----
intermolecular: hydrogen 0.5ev (per bond)
van der waals 0.1 per atom (or formula unit)

but the two matterials with highest boiling points are metals!
i haven't found any ion matterial that has higher boiling point...

can you point me where i could learn to calculate the exact bond energy?

 

[fargoth]

oops, haven't seen ZapperZ answered the OP...
id still like someone to show me where i could learn more about calculating bond energies though...

 

[Pieter Kuiper]

Covalent bonding is also important in transition metals. It is difficult to distinguish between these contribution. It is all calculated by the same programs.

When considering bonds, one might take into consideration that carbon i diamond only has only four bonds to nearest neighbours, where tungsten has eight (at room temperature) and rhenium has twelve.

 

[Intuitive]

hexagonal density makes for some very tough Material.