CARBON

Crystalline Amorphous

Diamond

Graphite

Fullerene

Coal

Charcoal

Lampblack

Allotropic forms of carbonAllotropic forms of carbon

Electronic configuration of CarbonElectronic configuration of Carbon

• C6 = 1s2 2s2 2px1 2py

1 2pz0

C

• *C6 = 1s2 2s1 2px1 2py

1 2pz1

1s 2s2p

C atoms in

graphite are sp2

hybridized

Sp2 Carbon

sp2 carbon has three hybrid orbitals at 120o

angle in one plane (forming sigma bonds with three such carbons) and a hybridized orbital at right angles to the plane.

Now each of these sp2 hybridized carbons combine with each other to form a sheet of

hexagonal arranged network.

Each C atom contains an unhybridized p orbital. Together due to resonance they form rings of delocalized electrons.

•Sheets of graphite are held together by weak van der waals forces of attraction to form many layers.

•Two sheets are separated by a distance of 3.4 Å.

•It is because of this that graphite molecules can slide over each other on application of force and graphite is a smooth material.

1.42 Ao

3.4 Ao

The delocalised electrons in the unhybridized p orbital are free to move anywhere within the sheet - each electron is no longer fixed to a particular carbon atom.

Because of these free electrons graphite is a good conductor of electricity.

There is, however, no direct contact between the delocalised electrons in one sheet and those in the neighbouring sheets.

Layer of C-atoms Delocalized

electrons

Properties of graphiteProperties of graphite• It has a high melting point

• It has a soft, slippery feel, and is used in pencils and as a dry lubricant for things like locks. You can think of graphite rather like a pack of cards - each card is strong, but the cards will slide over each other, or even fall off the pack altogether. When you use a pencil, sheets are rubbed off and stick to the paper.

• It is insoluble in water and organic solvents

• conducts electricity. The delocalised electrons are free to move throughout the sheets. If a piece of graphite is connected into a circuit, electrons can fall off one end of the sheet and be replaced with new ones at the other end.

CARBON

Crystalline Amorphous

Diamond

Graphite

Fullerene

Coal

Charcoal

Lampblack

Allotropic forms of carbonAllotropic forms of carbon

DiscoveryDiscovery

• The 1996 Nobel Prize for Chemistry has been won by Harold W. Kroto, Robert F. Curl and Richard E. Smalley for their discovery in 1985 of a new allotrope of carbon, in which the atoms are arranged in closed shells.

• It was discovered during the experiment of laser vaporization of graphite rod, under high vacuum chamber.

• This is because the graphite sheets break down to form spherical fullerenes.

StructureStructure

• Fullerenes are a cage like structure having formula C60,C70,C78.

• All carbon atoms in C60 are on the surface hence they are called ‘bucky balls ’

StructureStructure

• The structure of C60

resembles a soccer ball of the type made of 20 hexagons and 12 pentagons, with a carbon atom at the vertices of each polygon and a bond along each polygon edge.

• Only restriction is that no 2 pentagons touch each other.

• Diameter is 0.7 nm.• 30 (C=C) double bonds• FCC structure• Semiconductor• Pentagon sites in C60

are more strained than hexagonal sites therefore at high temp. molecules break at pentagonal sites

A soccer ball is a model of the Buckminsterfullerene C60

70-fullerene graph 60-fullerene graph

PropertiesProperties

• It has 60 vertices, 32 faces and a large number of symmetries.

• C60 is mustard colour and looks brown and black as its thickness increases.

• C=C bond length 1.38Ǻ

• C-C bond length 1.45Ǻ

• C60 has a tendency of avoiding having double bonds within the pentagonal rings which makes electron delocalization poor, and results in the fact that C60 is not aromatic.

PropertiesProperties

• Due to absence of aromatic character fullerenes behave like alkenes thus undergoing electrophilic addition.

• Physically bucky balls are extremely strong molecules being able to resist high pressures. They will bounce back to their original shape after being subjected to over 3000 atmospheres.

• Fullerene crystals are bonded weakly with each other by van der waals forces.

ApplicationsApplications

• Forms a superconductor with alkali metals

• Takes part in catalytic processes

• Used as a therapeutic & diagnostic agent due to size, stability and hydrophobic nature

• Acts as a potential inhibitor to HIV

• For trapping smaller size ions from solution of water

Singled Walled Carbon Nanotube (SWCNT)

• Cylinders made of graphite sheets, closed at the end with hemispherical fullerene or just by a graphite sheet cap.

• Formed by rolling a graphite sheet.

• Due to rolling some lattice strain is developed due to curvature in the carbon hexagons.

Types of CNT

• There are three types:

1. Zigzag

2. Armchair

3. Helical• Helical structure

shows a twisted looking structure.

Achiral

Chiral

Synthesis Of Carbon Nanotube

• Electric Arc Discharge• Chemical Vapour

Deposition• Laser Ablation (or

Vapourization)

Electric Arc Discharge

• Electric arc is struck between two graphite electrodes

• Electrodes:Graphite diameter of electrodes- 5 to 25 mm.

• Gap between electrodes: ~1 mm

• Current: 50 to 100 amps• Voltage: 15 to 25 volts• Gas pressure: He 100 to 500

torr

• When an electric arc is struck the temp reaches about 3000°C and anode evaporates and the CNT formed is deposited on cathode.The CNT are aligned in the direction of current between the electrodes. Adjustments of electrode gap without breaking the vacuum is essential, as the anode evaporates the gap increases

Chemical Vapour Deposition

Laser Ablation