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Why are diamond and graphite so different if both are pure carbon?

2003

Q. Dear Sirs,

I need to know the following issues due to my new presentation that I am going to make before my peers. I am designing a chemistry game with lots of questions in it. I deal with these technical issues as a hobby.

What determines whether a substance is transparent? For instance, why is silicon transparent when it is glass but not when it is sand or a computer chip?

How do rechargeable (that is, zinc-alkaline or nickel-cadmium) batteries work and what makes the reactions reversible in some batteries, but not in others?

How does the fluoride in toothpaste prevent cavities? Is there any kind of 'natural' fluoride protection, or is it only in artificial compounds?

How can graphite and diamond be so different if they are both composed of pure carbon?

Thank you in advance for your concern.

Best regards,

Doruk Gurkan
hobbyist - Istanbul, Turkey

A. Hello Doruk!

I can answer the one about graphite / diamond. The difference there is the atomic structure of the substance. Both have covalent bonding, with carbon atom connected to carbon atom: but in graphite the atoms are arranged in sheets, and in diamond the atoms are arranged in a cubic fashion. Well, not an actual cube: rather think of a cube with an atom on each corner, and four more atoms inside the cube. Upper atoms are at northwest and southeast, while lower atoms are northeast and southwest. With each carbon atom connected in a tetrahedron to four more atoms, it's a really stable structure. The sheet structure of the graphite makes for good lubricity, as the sheets slide well against each other, but poor mechanical properties.

Lee Gearhart
metallurgist - E. Aurora, New York
2003

Thanks a lot

Doruk Gurkan- THE SEZIN SCHOOL
(Sezin Lisesi)- Istanbul, Turkey
March 21, 2009