Carbon Allotropes and Intermolecular Forces

IB Topic 4: Bonding
pure carbon is covalently bonded in
three of different forms (allotropes)
1. graphite
2. diamond
3. fullerenes
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possesses a layer structure
 the layers of carbon atoms are arranged
in an repeating fashion
more compact structure and dense than
 one of the hardest materials known
highly stable chemically
 most famous is the “buckeyball”
› discovers awarded Nobel Prize in 1996
› over 1000 fullerene compounds have been made
composed of carbon atoms that form a
hollow, cage-like structure
› interesting feature of fullerenes is their ability to
enclose other atoms
forces that occur between molecules
 much weaker than intramolecular (within
the molecule) forces
› it takes 464 kJ/mol to break the H-O bonds within
a water molecule and only 19 kJ/mol to break
the bonds between water molecules
the strength of the intermolecular forces
determines the physical properties of the
› melting, boiling, reacting, solubility, conductivity,
 this will be covered in next PowerPoint
van der Walls YouTube (:20)
 also also known as London Dispersion
 even nonpolar molecules have forces that
hold them together
 the distribution of electrons around an
individual atom, at a given instant in time,
may not be perfectly symmetrical
› this can produce a temporary, instantaneous
dipoles (polar molecule)
› this can then induce a nearby molecule to be
polar and therefore a very weak attraction
between the two molecules
 and so on, and so on…
Sticky secret. Tiny hairs on
geckos' feet help maximize
contact with surfaces,
allowing van der Waals forces
to go to work.
attractive forces between the positive end
of one polar molecule and the negative
end of another polar molecule
 must be in close proximity for the dipoledipole forces to be significant
 stronger than van der Waal's forces
YouTube Hydrogen Bonding (1:40)
 YouTube Hydrogen Bonding Video (:58)
 a specific type of dipole-dipole type
 stronger than other dipole-dipole and/or
dispersion forces
 the hydrogen in a molecule (e.g. H-F, H-O
or H-N) is bonded to a small, highly
electronegative element (usually an F, O
or N atom) on another molecule

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