[gavindor]

I'm curious how these substances would be categorised..

Graphite - molecular?

Graphene - network solid?

Diamond - network solid?

C60 - molecular?

network solid being a macro-molecule

molecular being composed of molecules

network solid and molecular are mutually exclusive I think.. Is that right?

Graphene is a sheet of carbon bonded covalently..  That's a network solid (so, a macromolecule).

Graphite consists of sheets of Graphene, and the sheets are not bonded together covalently. So you have covalently bonded entities, connected together with ("intermolecular") - VDW forces..

With C60 it's molecular because one formula unit is a molecule but there'd be lots of C60 formula units.. each connected together with VDW forces.

Diamond is a network solid because it's all the atoms are in one group bonded covalently.  (not like with Graphite).  So it's a macromolecule. Like Graphene.

So do you agree with those categorisations?

Graphite as molecular?

Graphene as network solid?

Diamond as network solid?

C60 as molecular?

I understand that all of them consist of carbon and carbon only..  Graphite Graphene and Diamond having the same formula (C), but    buckminsterfullerene  having formula C60.  All allotropes of Carbon?

Thanks

[Aldebaran]

Graphite and diamond are generally regarded as giant covalent lattice structures ( or by similar meaning names e.g. networks) at least they are by UK exam boards. Similarity graphene being a one atom thick version of graphite. C60 is generally regarded as molecular. There are extensive explanations on Wikipedia.

[gavindor]

Graphite and diamond are generally regarded as giant covalent lattice structures ( or by similar meaning names e.g. networks) at least they are by UK exam boards. Similarity graphene being a one atom thick version of graphite. C60 is generally regarded as molecular. There are extensive explanations on Wikipedia.

C60 I can see as molecular.

I'm fine with diamond being giant covalent.. or graphene.

but it seems a bit problematic to me for Graphite to be classified as giant covalent

While graphite it seems isn't considered to be molecular , it seems to me that in a sense, graphite is molecular 'cos you have a repeating unit, each sheet of graphene..  Graphite is composed of macromolecules, (each macromolecule being a sheet of graphene)

Giant covalent is meant to be a macromolecule, fine for diamond, you have a  (mathematically) "connected network" , there's a path from one atom to any other atom, and all via covalent bonds. But with Graphite you don't have that. It seems really flawed to describe Graphite as a macromolecule.

I understand that methane doesn't contain hydrogen bonds..  If you froze methane, you'd have molecules of CH4 each connected with VDW interactions,  you wouldn't have a (mathematically connected network) of covalent bonds.  so it wouldn't be a macromolecule, it wouldn't be giant covalent. Likewise H2O  hydrogen bonds would exclude something from being a molecule. So Frozen water would not be a macromolecule, it wouldn't be giant covalent.  We can't really say Graphite is one big molecule / macromolecule, and hence  when drawing with a pencil , it draws.. as we know the sheets of graphene slip around and come off.  The sheets aren't bonded to each other.

Thanks

[Aldebaran]

The bonding in the layers of graphene are sp2 hybridised and it forms a giant covalent lattice. The bonds between the layers are considered metallic in character nd are weaker. IUPAC for example indicates their strength comparable to intermolecular forces. Nevertheless many authorities describe the structure of graphite as a giant covalent lattice. Understanding what’s going on is probably more important than what you choose to call it but in the UK the main exam boards, including Oxford, Cambridge and RSA expect to see graphite described as a giant covalent lattice even though that does not necessarily tell the whole story. So for students taking their exams it’s as well to be aware of their expectations. I would say you are not wrong in some of your thinking but be aware of the way various interpretations of the structure are described.

[gavindor]

The bonding in the layers of graphene are sp2 hybridised and it forms a giant covalent lattice. The bonds between the layers are considered metallic in character nd are weaker. IUPAC for example indicates their strength comparable to intermolecular forces. Nevertheless many authorities describe the structure of graphite as a giant covalent lattice. Understanding what’s going on is probably more important than what you choose to call it but in the UK the main exam boards, including Oxford, Cambridge and RSA expect to see graphite described as a giant covalent lattice even though that does not necessarily tell the whole story. So for students taking their exams it’s as well to be aware of their expectations. I would say you are not wrong in some of your thinking but be aware of the way various interpretations of the structure are described.

Thanks..

Do you know of any exam boards (not necessarily uk), or sources that consider Graphite to be not giant covalent (due to the non-covalent bonds between its graphene layers)?

I see you are very familiar with UK exam boards,  and ok they consider graphite to be giant covalent, would they consider Graphite to be a macromolecule?

[Aldebaran]

I am not aware of any authors who refer to graphite as not having a giant covalent structure (or similar terminology) and several authors do explicitly refer to both graphite and graphene as being examples of macromolecules (along with other commonly used examples of large molecular structures eg. proteins and synthetic polymers.
As stated in my previous post I think understanding what the effects and properties are which derive from or are related to their structure is more important than what terminology you choose to use; however generally speaking it's usually wise to follow commonly accepted terminology - especially when following a prescribed course of study with formal test and exams.

[gavindor]

ok thanks, so how do you define macromolecule?

[Aldebaran]

IUPAC has a definition you can Google as has Wikipedia.

[gavindor]

I see  for Graphite https://goldbook.iupac.org/terms/view/G02684   "The weak bonds between the layers are metallic with a strength comparable to van der Waals bonding only."

like you said

IUPAC has a definition you can Google as has Wikipedia.

Since you mention IUPAC, as for IUPAC, if you see

https://goldbook.iupac.org/terms/view/M03667  macromolecule (polymer molecule)  "A molecule of high relative molecular mass, the structure of which essentially comprises the multiple repetition of units derived, actually or conceptually, from molecules of low relative molecular mass."

Diamond is clearly a macromolecule but it doesn't really meet that IUPAC definition, does it? (Since Diamond isn't derived from molecules, it's derived from atoms).

Also it does say "A molecule of..".   Seems a bit funny to call graphite a molecule when it's kind of disconnected or some parts are only connected via intermolecular forces!

Thanks