Transcript Biology 2005N Paper 3 Option H

COVALENT NETWORKS
From : Tutorial on Allotropes of Carbon.
http://lawrencekok.blogspot.com
Prepared by
Lawrence Kok
https://www.youtube.com/watch?v=4XDJC64tDR0
Allotropes of Carbon
different form of an element in the same physical state
Diamond
Graphite
Graphene
Fullerene, C60
Allotropes of Carbon
Graphite
Diamond
Graphene
Fullerene, C60
Bond to 3 C atoms
…
Bond to 4 C atoms
Bond to 3 C atoms
• Carbon- sp3 hybridization
• Carbon- sp2 hybridization
•
Carbon- sp2 hybridization
• Strong hard covalent network
• Strong covalent network within layers
•
60 carbon atoms in sphere
• Weak Van Der Waals force bet layers
•
1 π electron free to delocalized.
•
Electrons NOT able to flow easily.
•
•
•
Carbon- sp2 hybridization
Carbon bond to 3 others form hexagon (120°)
Exist chicken wire/honeycomb- 1 layer
Allotropes of Carbon
Diamond
Graphite
Graphene
Fullerene, C60
Allotropes of Carbon
Diamond
Electrical conductivity
Poor
- No free moving electron
Graphite
Electrical conductivity
Good
- Within layer,
- ONE free delocalized π electron
Element exist in different form/physical state
Graphene
Electrical conductivity
Very Good
- Within layer
- ONE free delocalized π electron
moving across the layer easily
Fullerene, C60
Electrical conductivity
Semiconductor
- Surface sphere, not planar
- Some conductivity.
- Lower electron mobility
Allotropes of Carbon
Graphite
Diamond
Poor
- No free moving electron
Graphene
Electrical conductivity
Electrical conductivity
Element exist in different form/physical state
Good
Fullerene, C60
Electrical conductivity
Electrical conductivity
Semiconductor
Very Good
- Within layer
- ONE free delocalized π electron
- Within layer
- ONE free delocalized π electron
moving across the layer easily
- Surface sphere, not planar
- Some conductivity.
- Lower electron mobility
Special property
Special property
Special property
Special property
- Hardest substance
- Jewellery
- Soft, layer slide
across each other
Lightest/strongest material
replacing silicon in photovoltaic cell
Drug delivery
graphite
lubricant
electrode
Drug in graphene
Potential medicinal use
• Drug delivery
• Target cancer cells
Transistor/Electronic
Transparent conducting
electrode
Graphene
Fullerene, C60
Electron in hexagonal rings do not
delocalized over whole molecule.
Light and strong
Single sheet conductor
Potential medicinal use
• Trap/bind drug inside/outside cage
• Target cancer cells
Rool into conductive nanotubes
Graphene touch screen and photovoltaic cell
Electrical contact
photovoltaic cell
Drug inside
Click here to view touch screen
Click here for application of graphene
Lightest and strongest replacing silicon in photovoltaic cell
Drug bind outside
CNT = carbon nanotube
rool into
1 layer thick
rool into
Carbon Nanotube (CNT)
graphene
sp2 hybridization
•
•
•
•
Conduct current/heat very well
Conduct current at speed of light
Electron delocalized above/below plane
High electron mobility
Drug delivery to body
Attachment drug
therapeutics
Click here TEDtalk graphene
Click here to view
Silicon
Silicon dioxide
https://youtu.be/PiYnQLI-ufU
Silicon = Si
Silicon dioxide = sand = quartz
Silicon - sp3 hybridization
Silicon -sp3 hybridization
Giant lattice structure = covalent network
Strong
Semiconductor
Insoluble in water
Cannot form multiple bond ( larger size than C)
High melting point
Non-conductor of electricity
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