Graphene and graphite
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Layers of graphite is called graphene. But is graphene a different substance ?? I mean it a hydrocarbon so it is diferent from diamond, graphite and buckminster ?
Please also make clear whether the melting point of diamond is higher than graphite? Graphite is more stable than diamond in what terms.
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Originally posted by Kahynickel:
Layers of graphite is called graphene. But is graphene a different substance ?? I mean it a hydrocarbon so it is diferent from diamond, graphite and buckminster ?
Please also make clear whether the melting point of diamond is higher than graphite? Graphite is more stable than diamond in what terms.
Graphite and graphene may both be considered allotropes of carbon, but graphene is also the basic structural element of other carbon allotropes, including graphite (which is composed of layers of graphene stacked together with van der Waals interactions between graphene layers), carbon nanotubes and fullerenes (including Buckminsterfullerene).
The melting points of graphite and diamond are very similar, and pressure dependent. It's a common misconception among O level and A level students (and even some school teachers and private tutors) that the melting point of graphite is lower than diamond because less energy is required to overcome the weak van der Waals forces between graphene layers of graphite, compared to the tetrahedral giant covalent lattice structure of diamond. Because just overcoming the weak van der Waals forces allows you to write with a graphite pencil, but not melt it. To fully and properly melt graphite requires breaking the partial double bonds within each graphene layer, which brings us to the next point.
Graphite is more thermodynamically stable than diamond, because of the partial double bond character for each C-C bond in graphene / graphite. The stronger the bonds (and obviously the partial double C-C bonds in graphene / graphite, are stronger than the C-C single bonds in diamond), the more exothermic the bond formation enthalpy, and hence the more thermodynamically stable (as illustrated by the Gibbs free energy formula). -
But graphene is a hydrocarbon while graphite is C only. Do we incorporate Hydrogen in graphite by chemical reaction??
Secondly as you said and we know that both Diamond and graphite are carbon. both in their structure have many Carbon atom joined via covalent bonds. In polymer like poly(ethene) many small units add to produce a large unit which has highMr, while diamond has mass of 12 which is th Ar of one carbon atom. Why dont we consider the mass of all the carbon atom in diamond or graphite? Is it due to the reason that the number of atoms in Diamond cannot be counted. Is this the reason?
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Originally posted by Kahynickel:
But graphene is a hydrocarbon while graphite is C only. Do we incorporate Hydrogen in graphite by chemical reaction??
Secondly as you said and we know that both Diamond and graphite are carbon. both in their structure have many Carbon atom joined via covalent bonds. In polymer like poly(ethene) many small units add to produce a large unit which has highMr, while diamond has mass of 12 which is th Ar of one carbon atom. Why dont we consider the mass of all the carbon atom in diamond or graphite? Is it due to the reason that the number of atoms in Diamond cannot be counted. Is this the reason?
Graphene is pure C, no H.
Diamond and graphite is a giant covalent molecule, which means, depending on the exact size of the piece of diamond or graphite in your hand, there could be millions, tens of millions, hundreds of millions, billions, tens of billions, hundreds of billions of C atoms present. Eg. a piece of diamond which has a mass of 12g has 12/12 = 1 mol = 6.02214086 × 10^23 C atoms present. -
I am extremely sorry. I misread graphane as graphene. Actually graphane was given in an AQA question paper June 2013. It is a hydracarbon and as the name suggest -ane.
I still did not uderstand your avogadro-based explanation of diamond's atomic mass.
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Originally posted by Kahynickel:
I am extremely sorry. I misread graphane as graphene. Actually graphane was given in an AQA question paper June 2013. It is a hydracarbon and as the name suggest -ane.
I still did not uderstand your avogadro-based explanation of diamond's atomic mass.
Ah ok right. Graphane (CH)n, is basically hydrogenated graphene, with each C atom being sp3 hybridized instead of sp2. It can also be thought of as a 2D analog (ie. version) of diamond, but with each C atom bonded to a H atom (alternating above and below the sheet).
https://en.wikipedia.org/wiki/Graphane
About diamond, basically you're right, different pieces of diamond have different no. of C atoms, which is why there's no such thing as molar mass of diamond. To tell how many moles of C atoms are present in a piece of diamond, we take the sample mass of the diamond, and divide it by the molar mass of C, ie. 12g.