Divya1568
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Hi everyone! I need some help with this question. The answer to this question is B. Why is it not C ?
Carbon (diamond) and oxygen both form covalent bonds between their atoms in the
element.
What is the best reason for the fact that diamond has a much higher melting temperature than oxygen?
A Diamond is a solid but oxygen is a gas at room temperature.
B Diamond has a giant atomic structure but oxygen has a simple molecular
structure.
C The covalent bonds between carbon atoms in diamond are stronger than those between oxygen atoms.
D There is a single covalent bond between carbon atoms in diamond but a double covalent bond between oxygen atoms.
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Pigster
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(Original post by Vidya Das)
Hi everyone! I need some help with this question.
You have to think about what bond or force is being overcome when the change occurs.

In diamond, you need to break strong covalent bonds to melt/boil it.

In oxygen, you need to break weak intermolecular forces to melt/boil it.
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Lambert87
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Oxygen has intermolecular forces. These forces are weak and a small amount of energy is required to overcome these molecules. When sufficient energy has these intermolecular forces are broken.

Diamond on the other hand does not contain any intermolecular forces. Each carbon atom is covalently bonded to 3 other carbon atoms, a high amount of energy is needed to break the COVALENT bonds.

NO covalent bonds are broken in oxygen.
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Pigster
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(Original post by Lambert87)
Diamond...Each carbon atom is covalently bonded to 3 other carbon atoms...
4 other carbon atoms in diamond, 3 in graphite.
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Divya1568
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But why is the answer B?
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Maker
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The main different between C and O is C can form many bonds with itself and form a giant structure like diamond and graphite, a bit like a polymer.

O can only form bonds with one other O as in molecular oxygen or 2 other O as ozone.
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Divya1568
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I still don’t get it.
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Divya1568
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Question- Carbon (diamond) and oxygen both form covalent bonds between their atoms in the element. What is the best reason for the fact that diamond has a much higher melting temperature than oxygen?
A. Diamond is a solid but oxygen is a gas at room temperature.
B. Diamond has a giant atomic structure but oxygen has a simple molecular structure.
C. The covalent bonds between carbon atoms in diamond are stronger than those between oxygen atoms.
D. There is a single covalent bond between carbon atoms in diamond but a double covalent bond between oxygen atoms.
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Bulletzone
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"The strength of a covalent bond is measured by its bond dissociation energy, that is, the amount of energy required to break that particular bond in a mole of molecules. Multiple bonds are stronger than single bonds between the same atoms."

With Diamond, Each carbon can form 4 other carbon bonds to one another and if we theoretically had an infinite volume, It could go on for ever.
With Oxygen, All you need is 2 oxygen atoms and that is it. They form a double bond to one another and nothing else.
Here is a visual representation:
Image

Now Diamond could continue bonding forever and ever and ever............................ ...
Oxygen, It only forms a single bond with another Oxygen and that is it.

I'm sure you're aware of Intermolecular forces right? If you want to melt a Covalent compound, you would have to break the London Dispersion Forces (Van der waal forces) between the molecules.

The diamond I drew has an Mr of 264
The oxygen has an Mr of 32. (Oxygen wouldn't have Dipole-dipole as the polarities cancel due to it being Linear)

Which one would have more points of Interaction for Van der waal forces?
That's why Diamond has a higher Melting point.
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Divya1568
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(Original post by Bulletzone)
"The strength of a covalent bond is measured by its bond dissociation energy, that is, the amount of energy required to break that particular bond in a mole of molecules. Multiple bonds are stronger than single bonds between the same atoms."
With Diamond, Each carbon can form 4 other carbon bonds to one another and if we theoretically had an infinite volume, It could go on for ever.
With Oxygen, All you need is 2 oxygen atoms and that is it. They form a double bond to one another and nothing else.
Here is a visual representation:
Image

Now Diamond could continue bonding forever and ever and ever............................ ...
Oxygen, It only forms a single bond with another Oxygen and that is it.

I'm sure you're aware of Intermolecular forces right? If you want to melt a Covalent compound, you would have to break the London Dispersion Forces (Van der waal forces) between the molecules.

The diamond I drew has an Mr of 264
The oxygen has an Mr of 32. (Oxygen wouldn't have Dipole-dipole as the polarities cancel due to it being Linear)

Which one would have more points of Interaction for Van der waal forces?
That's why Diamond has a higher Melting point.
In the mark scheme, the answer given is B. But why is it not C ?
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Bulletzone
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(Original post by Vidya Das)
In the mark scheme, the answer given is B. But why is it not C ?
Physical properties (Melting and Boiling points) are governed by the inter-molecular forces - forces attracting one molecule to its neighbours - van der Waals attractions, Dipole Dipole or hydrogen bonds.
The bond strength is irrelevant unless you're talking about Ionisation energy and stuff.

Therefore the answer can not be C, but B.
Diamond being a macro molecule means there's more VDW forces hence the higher melting point.
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Divya1568
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(Original post by Bulletzone)
Physical properties (Melting and Boiling points) are governed by the inter-molecular forces - forces attracting one molecule to its neighbours - van der Waals attractions, Dipole Dipole or hydrogen bonds.
The bond strength is irrelevant unless you're talking about Ionisation energy and stuff.

Therefore the answer can not be C, but B.
Diamond being a macro molecule means there's more VDW forces hence the higher melting point.
Thank you so much for taking the trouble. 😊 Was trying to figure out this question for a long time
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Bulletzone
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(Original post by Vidya Das)
Thank you so much for taking the trouble. 😊 Was trying to figure out this question for a long time
Absolutely no problem.
I need every bit of revision tbh.
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Divya1568
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Size:  370.6 KB How do I solve this ???
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