Diamond & graphite are allotropes of carbon. Explain how they differ in terms of their molecular structure & why diamond is denser than..graphite?

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ndnordic's profile pic

ndnordic | High School Teacher | (Level 2) Associate Educator

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In diamond the carbon  atoms are bonded to one another in a 3-D array with every carbon atom bonded to four others in a tetrahedral shape.  In graphite each carbon atom is bonded to 3 others in a hexagonal flat shape.  The result is that diamond has a very stiff, rigid structure while graphite exists in sheets which can, to a degree, slide past each other.  Use the link below to build diamond and graphite.

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giorgiana1976 | College Teacher | (Level 3) Valedictorian

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Crystalline structure of diamond:

- Each carbon atom is  linked through four covalences by other four carbon atoms, using a tetrahedral orientation and having a sp3 hybridization → a crystal diamond seems to be a"Giant molecule".

- sp3 hybridized carbon atoms form powerful links, involve all the electrons in connection.

- carbon atoms have a tetrahedral geometry, which explain the physicochemical properties of diamond.

- The elementary cell of diamond is cubic.

Crystalline structure of graphite:

- Crystal is composed of flat layers of carbon atoms that are arranged in hexagons, as combs, and they are bound together by atomic ties, the  parallel planes of carbon atoms are linked by weak bonds, Van der Waals type;

- carbon atoms are Sp2 hybridized → those three links made with the three hybrid orbitals are strong, the third 2p orbital of each atom of the plan remains non-hybridized and contains a single electron

- all electrons of non-hybridized orbitals of atoms in a plane are common and mobile and they are belonging to all the atoms in the plane

- Elementary cell of graphite is of hexagonal type.

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