Boiling and Melting points Watch

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fares22

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Why is it that for some elements, you say that you need to break the intermolecular forces for it to boil or melt e.g. Chlorine but for others you have to break covalent bonds e.g. carbon. Does carbon not have any intermolecular forces?? or are the intermolecular forces only possible between molecules and a carbon atom isnt a molecule???

Please reply! got a mock tomorrow

Spannerin'moi

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(Original post by fares22)
Why is it that for some elements, you say that you need to break the intermolecular forces for it to boil or melt e.g. Chlorine but for others you have to break covalent bonds e.g. carbon. Does carbon not have any intermolecular forces?? or are the intermolecular forces only possible between molecules and a carbon atom isnt a molecule???

Please reply! got a mock tomorrow

https://www.khanacademy.org/test-pre...lecular-forces

fares22

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(Original post by Spannerin'moi)
https://www.khanacademy.org/test-pre...lecular-forces

i understand the difference between inter and intra. i just want to know why you have to break the covalent bonds in carbon for it to boil and not intermolecular forces like Cl2. does carbon not have intermolecular forces?

Spannerin'moi

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(Original post by fares22)
i understand the difference between inter and intra. i just want to know why you have to break the covalent bonds in carbon for it to boil and not intermolecular forces like Cl2. does carbon not have intermolecular forces?

When you say carbon, do you mean just as an atom? Or would you mean graphite ?The intermolecular bonds are still present in the case of graphite it holds the layers together but these forces are weak as compared to strong intramolecular giant covalent bonds. High energy is needed to break sea of covalent bonds and not much energy is required to break intermolecular forces as far as graphite is concerned.

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fares22

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(Original post by Spannerin'moi)
When you say carbon, do you mean just as an atom? Or would you mean graphite ?The intermolecular bonds are still present in the case of graphite it holds the layers together but these forces are weak as compared to strong intramolecular giant covalent bonds

i mean as an atom. carbon on its own is monatomic so this would mean it doesnt have any intermolecular forces. but chlorine is diatomic so it does?

are intermolecular forces only possible with atoms that are diatomic??

Spannerin'moi

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(Original post by fares22)
i mean as an atom. carbon on its own is monatomic so this would mean it doesnt have any intermolecular forces. but chlorine is diatomic so it does?

are intermolecular forces only possible with atoms that are diatomic??

http://intro.chem.okstate.edu/AP/Lec83101.html
Van der Waal intermolecular forces do exist between monoatomic substances...noble gases

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fares22

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(Original post by Spannerin'moi)
http://intro.chem.okstate.edu/AP/Lec83101.html
Van der Waal intermolecular forces do exist between monoatomic substances...noble gases

do they exsist in carbon?

ChemistryWebsite

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May I?

When considering melting points why are you considering monatomic carbon? carbon doesn't exist like that other than under extreme lab conditions.

Elemental carbon is macromolecular whether you consider graphire or diamond. A pieve of elemental carbon is effectively a single molecule. So there aren't intramolecular forces to breakdown - all the attraction forces that require breaking down are intramolecular, they are covalent bonds.

Boiling point of carbon is high because you need to melt it first.

fares22

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(Original post by TutorsChemistry)
May I?

When considering melting points why are you considering monatomic carbon? carbon doesn't exist like that other than under extreme lab conditions.

Elemental carbon is macromolecular whether you consider graphire or diamond. A pieve of elemental carbon is effectively a single molecule. So there aren't intramolecular forces to breakdown - all the attraction forces that require breaking down are intramolecular, they are covalent bonds.

Boiling point of carbon is high because you need to melt it first.

so carbon is always in a big structure. okay but how about other elements such as silicon? do they also only exsist as large structures so they dont have any intermolecular forces but covalent bonds

ChemistryWebsite

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(Original post by fares22)
so carbon is always in a big structure. okay but how about other elements such as silicon? do they also only exsist as large structures so they dont have any intermolecular forces but covalent bonds

Yes silicon is also macromolecular.

Learn your common macromolecules, you will need to know these to understand or predict melting point or boling point trends and more

fares22

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(Original post by TutorsChemistry)
Yes silicon is also macromolecular.

Learn your common macromolecules, you will need to know these to understand or predict melting point or boling point trends and more

just to make sure please.

Any element which is macromolecular will need covalent bonds to be broken when melted or boiled. this is because one of them is monatomic so there are no intermolecular forces

Thank you for your help!

ChemistryWebsite

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(Original post by fares22)
just to make sure please.

Any element which is macromolecular will need covalent bonds to be broken when melted or boiled. this is because one of them is monatomic so there are no intermolecular forces

Thank you for your help!

I think you still have the monatomic word buzzing around unnecessarily. Only the noble gases exist as monatomic molecules.
There are many elements (metals, Si, C for example) for which we don't have a specific number of atoms in their molecules, but please don't consider them monatomic - they have an unlimited number of atoms in their molecules.

You are correct that macromolecular elements will need many covalent bonds breaking. Not just elements though, macromolecular compounds such as SiO₂ also have many covalent bonds to break when you melt them.

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