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).
