Allotropes of Carbon

Diamond Graphite “Buckyballs” or buckminsterfullerene

Different structural/crystalline forms of the same element Allotrope definition Different structural/crystalline forms of the same element

Diamond Each carbon atom is bonded to 4 others to form a giant covalent network or lattice

Diamond Each carbon atom is bonded to 4 others to form a giant covalent network or lattice Is bond is of the same length and equally strong so the carbon atoms are sp3 hybridized

Diamond Each carbon atom is bonded to 4 others to form a giant covalent network or lattice Is bond is of the same length and equally strong so the carbon atoms are sp3 hybridized As all the electrons are localised (fixed in position), diamond is exceptionally hard and it does not conduct electricity

Diamond From: ibchem.com/IB/ibnotes/full/bon_htm/14.4.htm

Very high melting point Doesn’t conduct electricity Very hard Properties of Diamond Very high melting point Doesn’t conduct electricity Very hard

Graphite Each carbon atom is bonded to 3 other carbon atoms to give layers of hexagonal rings

Graphite Each carbon atom is bonded to 3 other carbon atoms to give layers of hexagonal rings As each bond is the same, the carbon atoms are sp2 hybridised

Graphite Each carbon atom is bonded to 3 other carbon atoms to give layers of hexagonal rings As each bond is the same, the carbon atoms are sp2 hybridised The remaining p orbital electron is delocalised to form weak bonds between the layers

Graphite Each carbon atom is bonded to 3 other carbon atoms to give layers of hexagonal rings As each bond is the same, the carbon atoms are sp2 hybridised The remaining p orbital electron is delocalised to form weak bonds between the layers The covalent layer lattice has all sigma bonds

Graphite From: http://physics.bu.edu/cc104/covalent.html

Graphite Because of the layers, graphite is an excellent lubricant as the layers can slide over each other

Graphite Because of the layers, graphite is an excellent lubricant as the layers can slide over each other Graphite is also a good conductor of electricity because of the delocalised electrons e.g. carbon rods, lead pencils

Buckminsterfullerene Is one member of a family of spherical carbon molecules sometimes called “buckyballs” Has the formula C60 The C atoms are arranged in hexagons and pentagons to give a geodesic spherical structure similar to a football

Buckminsterfullerene From: www.vega.org.uk/video/programme/65

Vancouver Geodesic From: http://www.flickr.com/photos/sharply_done/416104996/

Buckminsterfullerene Like in graphite, each carbon atom is bonded to 3 others

Buckminsterfullerene Like in graphite, each carbon atom is bonded to 3 others Each carbon atom is sp2 hybridized

Buckminsterfullerene Like in graphite, each carbon atom is bonded to 3 others Each carbon atom is sp2 hybridized There are also delocalized electrons, hence C60 can conduct electricity slightly

From: www.nanomaterialsdiscovery.com/technology.php...

Silicon Silicon dioxide - SiO2 From: http://www.galleries.com/minerals/elements/silicon/silicon.htm , www.fiji.hotel-pictures.com/.../beach2.html

Structure of Silicon Silicon contains 4 valence electrons It forms a lattice similar to that of diamond - each Si atom bonded to 4 others Silicon is fairly unreactive and acts as an insulator at low temperatures as it has no free electrons With impurities added it can conduct electricity at low temperatures From: http://web1.caryacademy.org/chemistry/rushin/StudentProjects/ElementWebSites/silicon/Structure.htm

Structure of silicon dioxide Commonly known as silica and seen as sand or quartz Like diamond, SiO2 is also a giant covalent lattice/ structure Each Si atom is bonded to 4 O atoms, and each O atom is bonded to 2 Si atoms From: http://www.moe.gov.sg/edumall/tl/digital_resources/chemistry6.htm , http://electronics.howstuffworks.com/quartz-watch2.htm

Properties of silicon dioxide has a high melting point - varying depending on what the particular structure is (remember that the structure given is only one of three possible structures), but around 1700°C. Very strong silicon-oxygen covalent bonds have to be broken throughout the structure before melting occurs. is hard. This is due to the need to break the very strong covalent bonds. doesn't conduct electricity. There aren't any delocalised electrons. All the electrons are held tightly between the atoms, and aren't free to move is insoluble in water and organic solvents. There are no possible attractions which could occur between solvent molecules and the silicon or oxygen atoms which could overcome the covalent bonds in the giant structure.