http://lawrencekok.blogspot.com

Prepared by Lawrence Kok

From : Tutorial on Allotropes of Carbon.

https://www.youtube.com/watch?v=4XDJC64tDR0

COVALENT NETWORKS

Allotropes of Carbon

different form of an element in the same physical state

Diamond Fullerene, C60GrapheneGraphite

Allotropes of Carbon

Diamond Fullerene, C60

• Carbon- sp2 hybridization

• 60 carbon atoms in sphere

• 1 π electron free to delocalized.

• Electrons NOT able to flow easily.

Graphene

• Carbon- sp2 hybridization• Carbon bond to 3 others form hexagon (120°) • Exist chicken wire/honeycomb- 1 layer

• Carbon- sp3 hybridization

• Strong hard covalent network

• Carbon- sp2 hybridization

• Strong covalent network within layers

• Weak Van Der Waals force bet layers

Graphite

Bond to 4 C atoms

Bond to 3 C atoms

Bond to 3 C atoms

…

Allotropes of Carbon

Diamond Fullerene, C60GrapheneGraphite

Allotropes of Carbon Element exist in different form/physical state

Diamond Fullerene, C60GrapheneGraphite

Electrical conductivity Electrical conductivity Electrical conductivity Electrical conductivity

Good

- Within layer, - ONE free delocalized π electron

Very Good

- Within layer- ONE free delocalized π electron moving across the layer easily

Poor

- No free moving electron

Semiconductor

- Surface sphere, not planar- Some conductivity.- Lower electron mobility

Allotropes of Carbon Element exist in different form/physical state

Diamond Fullerene, C60GrapheneGraphite

Electrical conductivity

Special property

Electrical conductivity Electrical conductivity Electrical conductivity

Special property

Good

- Within layer- ONE free delocalized π electron

Very Good

- Within layer- ONE free delocalized π electron moving across the layer easily

Poor

- No free moving electron

Semiconductor

- Surface sphere, not planar- Some conductivity.- Lower electron mobility

- Soft, layer slide across each other

- Hardest substance- Jewellery

Special property

graphite lubricant electrode

Lightest/strongest materialreplacing silicon in photovoltaic cell

Drug delivery Transistor/ElectronicTransparent conducting electrode

Drug in graphene

Potential medicinal use•Drug delivery •Target cancer cells

Special property

Fullerene, C60

Graphene

Click here to view touch screen

Electron in hexagonal rings do not delocalized over whole molecule.

Potential medicinal use•Trap/bind drug inside/outside cage•Target cancer cells

Drug inside Drug bind outside

Graphene touch screen and photovoltaic cell

Click here for application of graphene

Single sheet conductor Rool into conductive nanotubes

Electrical contact photovoltaic cell

Lightest and strongest replacing silicon in photovoltaic cell

Light and strong

• Conduct current/heat very well• Conduct current at speed of light • Electron delocalized above/below plane• High electron mobility

Click here to view

sp2 hybridization

graphene

rool into rool into

Carbon Nanotube (CNT)

Click here TEDtalk graphene

1 layer thick

Drug delivery to bodyAttachment drug therapeutics

CNT = carbon nanotube

https://youtu.be/PiYnQLI-ufU

Silicon Silicon dioxide

Silicon - sp3 hybridization

Giant lattice structure = covalent network

Semiconductor

Cannot form multiple bond ( larger size than C)

Silicon -sp3 hybridization

Strong

Insoluble in water

High melting point

Non-conductor of electricity

Silicon = Si Silicon dioxide = sand = quartz

Explain

Silicon dioxide cannot compete with the diversity possible in organic chemistry.However , there is evidence that the first forms of life were forms of clay minerals that were probably based on the silicon atom.

Why giant covalent substances (like diamond or silicon dioxide – sand) have very high melting points.

Lots (thousands, millions!) of atoms joined together by covalent bonds

• very strong bonds

• lots of bonds to be broken

• need a huge amount of energy/heat to break the bonds

• therefore a very high melting point