http://chenected.aiche.org/nanotechnology/mit-researchers-find-a-greener-way-to-grow-carbon-nanotubes/attachment/nanotubes-785px-flyingthroughnanotube/
Chemical Bonding 9
Giant Covalent Structures
Reference: Higher Level Chemistry, p. 124 - 127
1
IB Assessment Statements
4.2.9
Describe and compare the structure and bonding
in the three allotropes of carbon (diamond,
graphite and C60 fullerenes).
4.2.10
Describe the structure of and bonding in silicon
and silicon dioxide.
2
Covalent Substances
Almost all covalent substances are made of molecules,
either nonpolar or polar.
3
Giant Covalent vs Molecular Covalent Substances
Several covalent substances made of some Group 14 elements
form giant lattice structures instead of molecular structures.
a lattice structure
https://sites.google.com/site/apchemistryimfs/covalent-bonds
example: diamond
a molecular structure
www.wikimedia.com
example: methane (CH4)
4
Giant Covalent vs Molecular Covalent Substances
Molecular Covalent Substances - Structural Features
a molecular structure
smallest particle
= covalent molecule
(polar or nonpolar)
attractive forces between particles
= intermolecular forces
(dispersion, dipole-dipole, H-bond)
arrangement of particles
= variable, depending on state
state @ RT = solid, liquid or gas
example: methane (CH4)
(dependant on the strength of the IMFs)
London / dispersion forces (VDW)
5
Giant Covalent vs Molecular Covalent Substances
Giant Covalent Substances - Structural Features
a lattice structure
smallest particle = atoms
attractive forces between “particles”
= covalent bonds
arrangement of particles
= regular lattice structure
state @ RT = solid
https://sites.google.com/site/apchemistryimfs/covalent-bonds
example: diamond
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Giant (Network) Covalent Solids
Carbon and silicon form giant covalent network solids.
carbon allotropes*
* allotropes = different physical forms of an element
diamond
graphite
C60/fullerenes
(coal)
silicon & silicon dioxide
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Giant (Network) Covalent Solids
Carbon Allotropes 1: Structure of Diamond
http://www.chemguide.co.uk/atoms/structures/giantcov.html
http://johnblog.phychembio.com/?p=303
The smallest particle is a carbon atom.
Each carbon atom is covalently bonded to 4 other carbon atoms.
The arrangement around each carbon atom is tetrahedral,
with a bond angle of 109.5º. The carbon atoms show sp3 hybridisation.
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Giant (Network) Covalent Solids
Carbon Allotropes 1: Properties of Diamond
http://www.chemguide.co.uk/atoms/structures/giantcov.html
This structure is very stable due to the strong covalent
bonds and tetrahedral atom arrangement.
Diamond is NOT brittle and is the hardest known substance.
Diamond will NOT conduct electricity because there are
no mobile electrons or charged particles in the solid.
9
Giant (Network) Covalent Solids
Carbon Allotropes 2: Structure of Graphite
http://diariodeumquimicodigital.com/o-super-supercapacitor
The smallest particle is a carbon atom.
Each carbon atom is covalently bonded to 3 other carbon atoms.
Carbon atoms are arranged in hexagon rings, which then form sheets.
The arrangement around each carbon atom is trigonal planar,
with a bond angle of 120º. The carbon atoms show sp2 hybridisation.
London/dispersion forces hold the sheets together.
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Giant (Network) Covalent Solids
Carbon Allotropes 2: Properties of Graphite
The weak dispersion forces between the graphite sheets are easily
broken and account for these properties:
• graphite is brittle
• graphite is slippery ... layers slide over each other easily
∴ useful in pencils (!) and as a machinery lubricant
Graphite WILL conduct electricity because of the delocalized electrons in the
C=C bonds. Electrons can move around the carbon atoms inside one plane.
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Giant (Network) Covalent Solids
Carbon Allotropes 3: Structure of C60 (Fullerenes aka Buckyballs)
http://nano.gtri.gatech.edu/
http://www.chemistry.wustl.edu/~edudev/Fullerene/confirmation.html
The discovery of fullerenes opened up the field of nanotechnology.
The smallest particle is a carbon atom. There are 60 C atoms in a fullerene.
Each carbon atom is covalently bonded to 3 other carbon atoms.
Carbon atoms are arranged in pentagonal and hexagonal rings to form a sphere.
The arrangement around each carbon atom is trigonal planar, bond angle of 120º.
The carbon atoms show sp2 hybridisation.
12
Giant (Network) Covalent Solids
Carbon Allotropes 3: Properties of C60 (Fullerenes)
http://en.wikipedia.org/wiki/File:Endohedral_fullerene.png
Fullerenes are poor conductors of electricity. Even though there
are delocalized electrons WITHIN the molecules, the electrons do
not movement from one molecule to another.
Fullerenes have many possible applications. Look these up or read
the article posted on Moodle.
What is the most intriguing application to you?
13
Giant (Network) Covalent Solids
Carbon Allotropes 3: Other Interesting Carbon Structures
Nanotubes!
Find some cool uses of nanotubes!
14
Giant (Network) Covalent Solids
Elemental Silicon (Si): Structure
Silicon, like carbon, is group 14.
Silicon can form a giant covalent solid much like diamond:
The smallest particle is a silicon atom.
Each silcon atom is covalently bonded to 4 other silicon atoms.
The arrangement around each silicon atom is tetrahedral,
with a bond angle of 109.5º. The silicon atoms have sp3 hybridisation.
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Giant (Network) Covalent Solids
Elemental Silicon (Si): Properties
http://www.crazywebsite.com
Silicon is a semi-conductor of electricity.
Silicon has a high melting point, but it is less than that of diamond or carbon.
Suggest a reason for this. (Hint: think about bond energy values.)
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Giant (Network) Covalent Solids
Silicon Dioxide (SiO2): Structure
Watch out for this one!
The formula for silicon dioxide - SiO2 - makes many think it is made of molecules.
The formula
SiO2 refers to
the ratio of
atoms present.
http://www.chemguide.co.uk/inorganic/group4/oxides.html
http://www.chem.canterbury.ac.nz/letstalkchemistry/
electronicversion/electronicversionnew/chapter04/section4.shtml
The smallest particles are silicon and oxygen atoms.
Each silicon atom is covalently bonded to 4 oxygen atoms.
Each oxygen atom is covalently bonded to 2 silicon atoms.
The arrangement around each silicon atom is tetrahedral,
with a bond angle of 109.5º. Both silicon and oxygen atoms are sp3.
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Giant (Network) Covalent Solids
Silicon Dioxide (SiO2): Properties
quartz
sand
www.wikimedia.com
www.wikimedia.com
Silicon dioxide is insoluble in water.
It has a high melting point.
It is a poor conductor of heat and electricity.
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