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EXPLAIN IT WITH MOLECULES-- GRAPHITE AND DIAMOND


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 Jmol Applet]

Try this:

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 Jmol Applet]

Try this!!

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?

Please enter your answer in the space provided:


angstroms.

2) What is the distance of the CC bond in graphite?

angstroms

3)What is distance between the graphite layers?

angstroms

Multiple Choice Questions

1. Graphite is can be described as
a) hard and crystalline
b) soft and slippery
c) a dark liquid
d) made only of carbon and hydrogen atoms

2. Diamond is
a) made only of carbon and hydrogen atoms
b) the hardest substance know to man
c) soft and slippery
d) clear and brittle

3. What makes diamond so hard?
a) diamond has a crystal structure similar to ice
b) diamond is made up of only carbon atoms
c) the C-C bonds all have different bond lengths
d) a rigid network of atoms that cannot move

4. Which statement best describes why graphite is soft?
a) graphite is made up of only carbon atoms
b) graphite is layered
c) graphite has a low melting point
d) none of the above

5. Which of the following statements is not correct
a) both carbon and diamond are made of only carbon atoms
b) graphite has only weak forces between its layers
c) graphite and diamond have the same density
d) in diamond each carbon is the same distance to each of its neighboring carbon atoms

 


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