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gcse macromolecules

hi
so this might be a really dumb question but im so confused.

diamond has a high melting point right? apparently this is because carbon atoms in diamond are bonded covalently, so require a lot of energy to overcome. but i thought that when a substance changes state, the intermolecular forces weaken? the molecules themselves don't come apart, like when water evaporates the hydrogen and oxygen dont split?

why do the bonds within molecules in diamond weaken/break rather than the intermolecular forces weakening?
Reply 1
Original post by asbestos99
hi
so this might be a really dumb question but im so confused.

diamond has a high melting point right? apparently this is because carbon atoms in diamond are bonded covalently, so require a lot of energy to overcome. but i thought that when a substance changes state, the intermolecular forces weaken? the molecules themselves don't come apart, like when water evaporates the hydrogen and oxygen dont split?

why do the bonds within molecules in diamond weaken/break rather than the intermolecular forces weakening?

Hello! For simple covalent structures (the small ones) such as water, we talk about breaking the intermolecular forces. This is because you will never really just find one water molecule alone, there will be loads of them. So, when we melt or boil water, the weak intermolecular forces (forces between the molecules of water) will break which will result in, for example, water vapour instead of gaseous hydrogen and oxygen, as the covalent bonds do not break.

However, for macromolecular structures, these are just one massive molecule. Therefore, intermolecular forces (forces between different molecules) cannot exist, because there is simply only one molecule. Therefore, we must consider the INTRAmolecular forces (the covalent bonds). This is why when we are melting or boiling diamond for example, we are talking about breaking those carbon carbon covalent bonds which are much much stronger than intermolecular forces.

Hope this helps - any more questions let me know
Reply 2
You could think of diamond like one huge molecule because each carbon atom is covalently bonded to each other carbon atom. The actual covalent bonds between carbon atoms have to break to change state of diamond because there aren't any intermolecular forces to overcome. Intermolecular forces only occur between molecules, and if the chunk of diamond is just one big molecule, there aren't any intermolecular forces.
Reply 3
Original post by Maria303
Hello! For simple covalent structures (the small ones) such as water, we talk about breaking the intermolecular forces. This is because you will never really just find one water molecule alone, there will be loads of them. So, when we melt or boil water, the weak intermolecular forces (forces between the molecules of water) will break which will result in, for example, water vapour instead of gaseous hydrogen and oxygen, as the covalent bonds do not break.

However, for macromolecular structures, these are just one massive molecule. Therefore, intermolecular forces (forces between different molecules) cannot exist, because there is simply only one molecule. Therefore, we must consider the INTRAmolecular forces (the covalent bonds). This is why when we are melting or boiling diamond for example, we are talking about breaking those carbon carbon covalent bonds which are much much stronger than intermolecular forces.

Hope this helps - any more questions let me know


you beat me haha
Reply 4
Original post by 0gg
you beat me haha

Haha only just!
Reply 5
Original post by Maria303
Hello! For simple covalent structures (the small ones) such as water, we talk about breaking the intermolecular forces. This is because you will never really just find one water molecule alone, there will be loads of them. So, when we melt or boil water, the weak intermolecular forces (forces between the molecules of water) will break which will result in, for example, water vapour instead of gaseous hydrogen and oxygen, as the covalent bonds do not break.

However, for macromolecular structures, these are just one massive molecule. Therefore, intermolecular forces (forces between different molecules) cannot exist, because there is simply only one molecule. Therefore, we must consider the INTRAmolecular forces (the covalent bonds). This is why when we are melting or boiling diamond for example, we are talking about breaking those carbon carbon covalent bonds which are much much stronger than intermolecular forces.

Hope this helps - any more questions let me know

oh my god thank you so much! this makes loads more sense, especially the bit about macromolecular structures being one big molecule with intramolecular forces. i'd never thought about it that way!

thank you!!!! have a great evening
Reply 6
Original post by 0gg
You could think of diamond like one huge molecule because each carbon atom is covalently bonded to each other carbon atom. The actual covalent bonds between carbon atoms have to break to change state of diamond because there aren't any intermolecular forces to overcome. Intermolecular forces only occur between molecules, and if the chunk of diamond is just one big molecule, there aren't any intermolecular forces.

thanks so much for taking the time to reply, this is super helpful!
this is exactly what i didnt get when i asked my chemistry teacher lol
have an amazing evening :biggrin:
(edited 7 months ago)
Reply 7
Original post by asbestos99
thanks so much for taking the time to reply, this is super helpful!
this is exactly what i didnt get when i asked my chemistry teacher lol
have an amazing evening :biggrin:

You too!! Glad I could help (:

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