Atoms of the same element are identical. why is it that diomand and graphite both made of carbon atoms are so different?

Answer 1

Both are pure carbon compounds, but the difference is in how these atoms are bonded to each other. Carbon pretty much always forms four bonds to other atoms. In a diamond, each bond is a single bond that connects the carbon atoms in a tetrahedral network. (Since each carbon bonds to four other carbons, the best way to arrange this spatially is to form a tetrahedron). In graphite, the carbons are bonded much differently. I am not sure if you are familiar with a benzene ring: it is six carbon atoms arranged in a hexagon. The bonds alternate single bond, double bound, single bond, double bond, etc. around the hexagon. A single unit is called benzene. Two hexagons fused together (to form a ten sided figure) is called naphthaline, and three hexagons fused in a line is called anthracene. Well imagine millions of hexagons all fused together in a giant honeycomb-like arrangement - this is what graphite looks like. These "sheets" are stacked on top of one another in layers. That is why graphite can "rub off" so easily - it is just the layers sliding past one another. It is also why graphite can conduct electricity (electrons are free to flow through the highly conjugated pi system) and diamond cannot (no way for electrons to flow through the sigma bonding system).