Allotropes of Carbon

Graphene

- a single layer of graphite -very good electrical and thermal conductor -high melting point

silicon dioxide

-SiO2 -Giant covalent structure -each silicon bonded to four oxygen atoms, each oxygen is bonded to two silicon atoms -basic shape is bent due to two lone pairs on the oxygen atom -high melting and boiling points, covalent bonds

Diamond

-giant covalent (macromolecular) structure - each carbon is bonded to 4 others (sp3 hybridized) -very high melting and boiling point, because energy must be supplied to break covalent bonds - very hard -does not conduct electricity, all electrons are held in covalent bonds and are not free to move -not soluble in water or organic solvents because the forces between the atoms are too strong

Graphite

-giant covalent structure -layered structure, each carbon is bonded to three others in a trigonal planar array (sp2 hybridized) -Covalent bonds between the carbons, but London forces between the layers -weak forces between the layers is an explanation for graphite as a good lubricant( used in pencils) -very high melting and boiling point because covalent bonds within layers must be broken -non soluble in water or non-polar solvents, due to covalent bonds -conducts electricity because each carbon has extra electrons, delocalized system

C60 Fullerene

-molecular structure, only London forces must be overcome when fullerene melts -substantially lower boiling point than graphite and diamond -hexagons and pentagons -insoluble in water but soluble in some organic solvents, such as benzene -does not conduct electricity -sp2 hybridized

Fullerene C60

each C atom is sp2 hybridized, bonded in a sphere of 60 carbon atoms, consisting of 12 pentagons and 20 hexagons. Structure Is a closed spherical cage in which each carbon is bonded to 3 others. -easily accepts electrons to form negative ions; a semiconductor at normal temp and pressure due to some electron mobility -yellow crystalline solid, soluble In benzene -Reacts with K to make superconducting crystalline material;related forms are used to make nanotubes for the electronics industry, catalysts and lubricants

Graphite

Each C atom is sp2 hybridized covalently bonded to 3 others, forming hexagons in parallel layers with bond angles of 120. The layers are held only by weak van der waals forces so they can slide over each other -contains only one non-bonded, delocalized electron per atom; conducts electricity due to the mobility of these electrons -Non-lustrous, grey solid - used as lubricant and in pencils -giant macromolecular

Diamond

Each C atom is sp3 hybridized covalently bonded to 4 others tetrahedrally arranged in a regular repetitive pattern with bond angles of 109.5. It Is the hardest known natural substance. -all electrons are bonded; non-conductor of electricity because there are no mobile electrons -lustrous crystal -polished for jewelry and machinery for grinding and cutting glass -giant macromolecular