Why is Graphite soft and Diamond hard if both are pure carbon?
Carbon alone forms the familiar substances graphite and diamond. Both graphite and diamond are made only of carbon atoms. Graphite is very soft and slippery. Diamond is the hardest substance known to man. If both are made only of carbon what gives them different properties?
The answer lies in the way the carbon atoms form bonds with each other.
[Graphite structure shown using the Jsmol]
Rotate the Graphite molecule
( Hold the left mouse button down over the java applet image and move the mouse to rotate the graphite molecule).
Notice that graphite is layered.
While there are strong covalent bonds between carbon atoms in each layer, there are only weak forces between layers. This allows layers of carbon to slide over each other in graphite.
On the other hand, in diamond each carbon atom is the same distance to each of its neighboring carbon atoms. In this rigid network atoms cannot move. This explains why diamonds are so hard and have such a high melting point.
[Diamond structure shown using the Jsmol]
Rotate the structure of diamond --
Notice that each diamond atom is the same distance to each of its neighboring carbon atoms. There is a rigid network of bonds within the diamond crystal.
What is the bond length for a diamond C-C bond?
1) What is the distance of the CC bond in diamond?
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