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By Ashish
Diamond and graphite
are two allotropes of the same element (carbon) and the differences in their
properties are a result of the way their crystal structures are arranged.
Both diamond and
graphite are made of pure carbon, yet they have dramatic differences in their
properties.
As allotropes of the
same element, you might expect them to share many similarities, but that simply
isn’t the case.
At first, this
question might seem odd to many people. Diamond and graphite… doesn’t sound
like a particularly sensible combination.
Diamond and gold, or
diamond and sapphire would make more sense, right?
So, why is diamond
pitted in the same category with graphite – the thing that we find inside our
pencils?
Well, if you had paid
attention to your Chemistry lessons in high school, you would know that there
is, in fact, a very strong structural connection between the two.
What’s the connection
between the two? And why are they so different from each other?
What are allotropes?
Allotropy (also
referred to as ‘allotropism’) of an element is that element’s ability to exist
in multiple forms in the same physical state with a different arrangement of
its atoms.
The different forms
are called allotropes of the given chemical element.
Triangle Rectangle & square shapes 36 ball |
The constituent
pieces of these shapes (balls) represent atoms, and the different shapes they
assume (due to their varied arrangements) are the allotropes.
Allotropes of the
same element have different bonding arrangements, which give rise to different
chemical and physical properties for the substance.
Allotropes of Phosphorus & Allotropes of Oxygen |
The following image
features various allotropes of phosphorus and oxygen.
Allotropes of carbon
In the world of
allotropes, the carbon is nothing less than a rockstar. It has the ability to
form many allotropes, thanks to its chemical structure.
Its atomic number is
6, which means that it has 4 electrons in its valence shell.
Different allotropes of carbon |
However, out of all
the known allotropes, the most popular ones are diamond and graphite.
These two allotropes,
which visually appear incredibly different, are still made of nothing but
carbon.
Although their
composition is the same, they exhibit different chemical and physical
properties, thanks to the arrangement of carbon atoms within them.
Why is diamond hard,
but graphite is soft, despite being composed of the same element (carbon)?
It boils down to a
single factor: geometry.
Diamond Structure |
This crystal
arrangement is energetically very favorable and imparts that characteristic
strength, durability and rigidity to diamond.
To scratch or break
it requires a high amount of force, which makes it one of the hardest
naturally-occurring materials on the planet.
Graphite, on the
other hand, has an entirely different geometric arrangement than diamond.
Its carbon atoms are
arranged in 2D sheets, whereas each carbon atom is bonded to three other carbon
atoms to form hexagonal rings in an infinite array.
graphite-structure |
The result of this is
that the layers slide over each and can detach from each other very easily.
These weak bonds
between the multiple sheets of carbon atoms make the graphite used in pencils
flake off on paper, allowing you to write.
In addition to being
soft and slippery, graphite also has a much lower density than diamond.
The one thing about
all of this that amazes me most is how a few tweaks in the chemical structure
of identical substances make them so massively different in their appearance,
toughness and chemical properties!
Ashish is a
Science graduate (Bachelor of Science) from Punjabi University (India). He
spends a lot of time watching movies, and an awful lot more time discussing
them. He likes Harry Potter and the Avengers, and obsesses over how thoroughly
Science dictates every aspect of life… in this universe, at least.
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