Ask A Scientist Chemistry Archive

name         Ng Chong S.
status       student
age          17
  
molecules bonded together in quadruplet form. If this is so, what happens
to the bond at the edge or surface of a diamond? ie: is it still bonded
together with other carbon atoms in quadruplet bond?
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Perceptive question, and it really generalizes to the surface of any
substance, especially those that are not crystals of discrete molecules.
This is an interesting, but difficult area to study for the reason (among
others) that there is not much surface to study. The general answer is that
the structure of the "surface" [I use "...."] because what constitutes the
"surface" is often unclear and may extend some distance beneath the
"surface". That point aside, how crystals terminate on the surface is
variable -- depending upon the substance, and the surroundings to which it
is exposed, e.g. air, water, solvent.

Graphite is one of the more thoroughly studied surfaces. It terminates at
the ends of the layers by reacting with oxygen to form quinones, and hydro
quinones. Glass (SiO2) generally terminates with the formation of
hydroxides, or hydrogen ions and possibly a counter ion. Metals, under
atmospheric conditions terminate by forming oxides of various compositions,
depending upon the metal . In any of these cases there can also be some
bridging between adsorbed functionality.

So your question does not have a unique answer.

Vince Calder
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If a diamond is freshly cleaved, the bonds at the surface are broken in half,
leaving behind what are know as "dangling bonds", which are actually free
radicals.  If these free radicals do not bond to something fairly quickly
(if the surface is cleaved in a hard vacuum), they will rearrange so that
they bond to each other, making a graphite pattern.  Since graphite at
standard temperatures and pressures is stabler than diamond, this graphite
pattern at the surface slowly influences the carbon atoms in adjacent layers
to also rearrange into the graphite pattern, eventually turning the whole
diamond into graphite.

Most diamond surfaces are terminated with C-H bonds.  If the diamond is
cleaved in the presence of a hydrogen atom donor, the broken bonds can take
on hydrogen, preventing the lattice from converting into graphite.

Richard E. Barrans Jr., Ph.D.
Assistant Director, PG Research Foundation
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Typically, the bonds at the surface of a diamond are terminated by
hydrogen atoms.

Greg Bradburn
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