4.3 ALLOTROPES OF CARBON & COVALENT NETWORKS
*Allotropes  different structural forms or modifications of the______________element that differ in _______________ and ________________ properties
*Covalent Network / Giant Molecular  regular ________________ bonds, but they exist between _________ atoms in a giant three-dimensional array – that is,
every atom is covalently bonded to all its nearest neighbours. In effect, a covalent network is one very large molecule.
Covalent
Network or
Molecular?
Geometry
Diamond
Graphite
Graphene (2004)
C60 Fullerene (1985)
-each carbon atom bonded to
______ other carbons in a
___________________
arrangement of carbons
-layers (“sheets”) of hexagonal
rings of carbon atoms
-geometry of each carbon is
____________ planar
-single, planar sheet of carbon
atoms arranged hexagonally
-one atom thick (one of the
-spherical molecules consisting
of _____ carbon atoms
-icosahedral (polygon with
_____ faces) cage (shape of
soccer ball)
thinnest and strongest materials
known) ; essentially graphite
prised apart
Hybridization
Conductivity
__________ – all electrons are
used in localized bonds
________ – only ___ electrons
from each carbon are used in
bonding – the fourth electron is
found in a ________________
pi “cloud” formed by
unhybridized ___ - orbitals
-_____________ (300 times
more efficient than copper)
-none (although delocalized
electrons present ; electrons
incapable of moving from one
molecule to the next)
Melting Point
(°C)
Solubility
3550
Approx. 3675
Sublimates at 600
insoluble
insoluble
Approx. 3625 (one of highest
known)
insoluble
Hardness /
Strength
Very ________ – all atoms are
held together in the lattice by
strong ___________ bonds
Very _______ –
layers slide over each other
because of weak
_______________forces
between the layers
*between 1 & 2 on Mohs scale
*10 on Mohs scale
(Steel is 4.5 – 5 on the scale!)
-extremely strong, flexible and
transparent
*>10 on Mohs scale
-insoluble in water (can
dissolve in some non-polar
solvents such as __________)
-weak _________ forces
between C60 molecules
Some Uses
-heavy-duty cutting tools (e.g.,
saws, polishing tools, dental
drills)
-pencil ‘lead’
-machine lubricant
-potential to replace metals
-inclusion complexes (enclosed
used in the aerospace industry
-LCD screens
atoms or small molecules
within fullerene cage)
potentially used as gene and
drug carriers, and in
superconductivity
-inhibit HIV related enzymes
Other Examples of Covalent Networks:
Silicon
Geometry
*Silicon Dioxide (SiO2), Quartz / Silica
*Quartz: same as diamond structure
Silicon Carbide (SiC / Moissonite)
Conductivity
Hybridization
Melting Point (°C)
Solubility
Semiconductor
*Silica = sand (amorphous…no ordered
structure)
Solid – none ; Molten - conducts
1400
1710
2700
-insoluble
-insoluble
-insoluble
Hardness
Some Uses
7.0 on Mohs scale
-electronic components
-computer chips
7.0 on Mohs scale
-use in optical and scientific instruments
-electronics (e.g. quartz watch)
9 - 9.5 on Mohs scale
-diamond alternative
- SiC powder = an abrasive
- car parts
-bulletproof vests
Periodic Table of Videos:
Buckyballs (fullerenes): https://www.youtube.com/watch?v=ljF5QhD5hnI
Graphene: https://www.youtube.com/watch?v=prKi2TI0TVw
Carbon / allotropes of Carbon: https://www.youtube.com/watch?v=QuW4_bRHbUk
Silicon: https://www.youtube.com/watch?v=a2aWO5cL410
semiconductor