Allotropy
Done by Sun Yudong 1O227
1
What is allotropy?
of an element existing in
two or more physical forms
• the property of some chemical elements to
exist in two or more different forms
– known as allotropes of these elements
• different structural modifications of an
element
2
What about allotropes?
• a structurally different
• forms of the same element which exhibit
different physical properties.
– different physical properties displayed by
allotropes of an element
• atoms are arranged into molecules or crystals in
different ways.
• Some allotropes of an element may be more
chemically stable than others.
3
• Elements such as
4
• Allotropy refers
– i.e. different solid, liquid or gas forms
• The changes of state between solid, liquid and
gas in themselves are not considered
allotropy.
• e.g. →
5
Common
Allotropes
– 4 common
– atoms bonded together in a tetrahedral lattice arrangement
– atoms bonded together in sheets of a hexagonal lattice
•
– single sheets of graphite
– atoms are bonded together in spherical, tubular, or ellipsoidal
formations
6
Allotropes
• For some elements, allotropes have different
molecular formulae which can persist in
different phases
– E.g.. 2 allotropes of
• Oxygen Gas(dioxygen)(O2 )
• Ozone (O3)
can both exist in the solid, liquid and gaseous
states.
7
Allotropes
• Conversely, some elements do not maintain
distinct allotropes in different phases
– E.g.
• has numerous solid allotropes
– all revert to the same P4 form when melted to the liquid state.
Pure phosphorus exists in several forms called allotropes. This photo shows waxy
white phosphorus (yellow cut), red phosphorus, violet phosphorus and black
phosphorus. The allotropes of phosphorus have markedly different properties from
each other.
8
List of Elements with Allotropes
(Some Non-metals and metalloids)
9
Some Elements with Allotropes
(Metals(at ambient pressure))
10
Some Elements with Allotropes
(Metals(Considering only the technologically-relevant metals))
at 882°C
at 912°C and 1394°C
at 422°C
at 863°C
at 13°C
at 668˚C and 776˚C
11
6th element of the periodic table
ALLOTROPES OF
12
• Allotropes
• Graphene
or buckytube (h)
• Buckminsterfullerene or
buckyball
– Carbon nanotubes
» Carbon nanobuds
–
–
–
–
Glassy carbon
Atomic and diatomic carbon
Carbon nanofoam
Linear acetylenic carbon (LAC)
• A one-dimensional carbon
polymer with the structure (C:::C)n-
13
Diamond
• an extremely hard, transparent crystal, with the carbon
atoms arranged in a tetrahedral lattice.
• A poor electrical conductor.
• An excellent thermal conductor.
• one of the best known allotropes of
• hardness and high dispersion of light
– make it useful for both industrial applications and
jewellery
• Diamond is less stable than graphite
– but the conversion rate from diamond to graphite is
negligible at ambient conditions.
14
Diamond
• Diamond has remarkable optical
characteristics.
• Due to its extremely rigid lattice, it can be
contaminated by very few types of impurities,
such as
and
.
WellPromo.com
15
Diamond
• Small amounts of defects or impurities (about one per
million of lattice atoms) colour diamond
–
–
–
–
–
–
–
–
blue (
)
yellow (
)
brown (lattice defects)
green (radiation exposure)
Purple
Pink
Orange
Red.
• Diamond also has relatively high optical dispersion (ability
to disperse light of different colours), which results in its
characteristic luster.
16
Diamonds
• Most natural diamonds are formed at highpressure high-temperature conditions existing
at depths of 140 to 190 kilometres in the Earth
mantle.
• Carbon-containing minerals provide the
carbon source
• the growth occurs over periods from 1 billion
to 3.3 billion years
– (25% to 75% of the age of the Earth)
17
Diamonds
• Answer?
– Diamonds are brought close to the Earth surface
through deep volcanic eruptions by a magma,
which cools into igneous rocks known as
kimberlites and lamproites.
18
Diamonds
• Then where do they get so many diamonds?
– Synthetic
• Diamonds can also be produced synthetically in a highpressure high-temperature process which
approximately simulates the conditions in the Earth
mantle.
• Chemical Vapour Deposition (CVD).
– Several non-diamond materials, which include cubic zirconia
and
and are often called
,
19
A rough natural Diamond
20
Diamonds
• Special gemmological techniques have been
developed to distinguish natural and synthetic
diamonds and diamond simulants.
21
Diamond
• The most popular gemstone. Why?
– Excellent optical
– Excellent mechanical properties
– efficient marketing
22
Graphite
• a soft, black, flaky solid, a moderate electrical
conductor.
• The C atoms are bonded in flat hexagonal
lattices (graphene), which are then layered in
sheets.
23
Graphite
• Naturally found in Sri Lanka,
Canada and the United States.
• Named by Abraham Gottlob
Werner in 1789 from the Ancient
Greek γράφω (graphō), “to
draw/write”
• Named for its use in pencils,
where it is commonly called lead
24
Graphite
• Made of layers of carbon atoms
– These layers can slide over each other very easily.
• meaning that it is very soft
• Unlike diamond, graphite is an electrical conductor, a
semimetal.
• Due to the delocalized electrons between the layers, it
can conduct electricity very well.
• Graphite is the most stable form of carbon under
standard conditions.
– Thus, used in thermochemistry as the standard state for
defining the heat of formation of carbon compounds.
25
Graphite
• Graphite can be formed
from coal put under high
heat and pressure.
• Graphite can also be
turned into diamond with
enough heat and
pressure.
– This is one way how
synthetic diamonds are
made.
26
Graphite
• Some uses
– It can be used as a lubricant to make mechanical
devices run smoother.
– The most common use of graphite is the "lead" in
a pencil, which also has clay.
27
Graphene
• an allotrope of carbon
• structure is one-atom-thick planar sheets of
sp2-bonded carbon atoms that are densely
packed in a honeycomb crystal lattice
Graphene is an atomic-scale honeycomb lattice
made of carbon atoms.
28
Graphene
• A single layer of graphite is called graphene
and has extraordinary electrical, thermal, and
physical properties.
• It can be produced by epitaxy on an insulating
or conducting substrate or by mechanical
exfoliation (repeated peeling) from graphite.
• Its applications may include replacing silicon in
high-performance electronic devices.
29
Graphene
• Graphene is most easily visualized as an atomicscale chicken wire made of carbon atoms and
their bonds.
• The crystalline or "flake" form of graphite consists
of many graphene sheets stacked together.
• The carbon-carbon bond length in graphene is
about 0.142 nanometers.
• Graphene sheets stack to form graphite with an
interplanar spacing of 0.335 nm
– which means that a stack of three million sheets
would be only one millimeter thick.
30
Graphene
• Graphene is the basic structural element of
some carbon allotropes including
– Graphite
– Charcoal
– Carbon nanotubes
– Fullerenes
Graphene Paper
31
Lonsdaleite
• named in honour of Kathleen Lonsdale
• an allotrope of carbon with a hexagonal lattice
• also called hexagonal diamond
– in reference to the crystal structure
Crystal structure of Lonsdaleite
32
Lonsdaleite
• In nature, it forms when meteorites containing
graphite strike the Earth.
– The great heat and stress of the impact transforms
the graphite into diamond, but retains graphite's
hexagonal crystal lattice.
• first identified in 1967 from the Canyon Diablo
meteorite, where it occurs as microscopic
crystals associated with diamond
33
Amorphous carbon
• Amorphous carbon is the name used
for carbon that does not have any
crystalline structure.
• As with all glassy materials, some
short-range order can be observed,
but there is no long-range pattern of
atomic positions.
• While entirely amorphous carbon can
be produced, most amorphous carbon
actually contains microscopic crystals
of graphite-like, or even diamond-like
carbon.
34
Amorphous carbon
• Coal and soot or carbon black are informally called
amorphous carbon.
– However, they are products of pyrolysis (the process of
decomposing a substance by the action of heat), which
does not produce true amorphous carbon under normal
conditions.
– The coal industry divides coal up into various grades
depending on the amount of carbon present in the sample
compared to the amount of impurities.
– The highest grade, anthracite, is about 90% carbon and
10% other elements.
– Bituminous coal is about 75-90% carbon, and lignite is the
name for coal that is around 55% carbon.
35
Buckminsterfullerenes
• C60
• The buckminsterfullerenes (or usually just fullerenes or buckyballs for
short) were discovered in 1985 by a team of scientists from
Rice University and the University of Sussex
– three of whom were awarded the 1996 Nobel Prize in
Chemistry.
• They are named for the resemblance of their alliotropic
structure to the geodesic structures devised by the scientist
and architect Richard Buckminster "Bucky" Fuller.
• Fullerenes are molecules of varying sizes composed entirely
of carbon, which take the form of a hollow sphere,
ellipsoid, or tube.
36
Buckministerfullerenes
• As of the early twenty-first century, the
chemical and physical properties of fullerenes
are still under heavy study, in both pure and
applied research labs.
• In April 2003, fullerenes were under study for
potential medicinal use — binding specific
antibiotics to the structure to target resistant
bacteria and even target certain cancer cells
such as melanoma.
37
Carbon nanotubes
• Carbon nanotubes, also called
buckytubes, are cylindrical carbon
molecules with novel properties that
make them potentially useful in a
wide variety of applications
– e.g., nano-electronics, optics,
materials applications, etc.
• They exhibit extraordinary strength,
unique electrical properties, and are
efficient conductors of heat.
38
Carbon nanobuds
• Carbon nanobuds are a newly
discovered allotrope of carbon
in which fullerene like "buds"
are covalently attached to the
outer sidewalls of the carbon
nanotubes.
• This hybrid material has useful
properties of both fullerenes
and carbon nanotubes.
• In particular, they have been
found to be exceptionally good
field emitters.
Computer models of several stable
nanobud structures
39
Glassy carbon
• or vitreous carbon
• is a class of non-graphitizing carbon widely used
as
– An electrode material in electrochemistry
– For high temperature crucibles
– As a component of some prosthetic devices.
• can be fabricated as different shapes, sizes and
sections, is a non-graphitizing carbon
– which combines glassy and ceramic properties with
those of graphite.
40
Glassy Carbon
• It was first produced by Bernard
Redfern in the mid 1950s at the
laboratories of The Carborundum
Company, Manchester, UK.
• He had set out to develop a polymer
matrix to mirror a diamond
structure and discovered a resole
(phenolic) resin that would, with
special preparation, set without a
catalyst.
• Using this resin the first glassy
carbon was produced.
A small rod of glassy carbon.
41
Atomic and diatomic carbon
• Under certain conditions, carbon can be found in
its atomic form.
• It is formed by passing large electric currents
through carbon under very low pressures.
• It is extremely unstable, but it is an intermittent
product used in the creation of carbenes.
• Diatomic carbon can also be found under certain
conditions.
• It is often detected via spectroscopy in extraterrestrial bodies, including comets and certain
stars.
42
Atomic carbon
Making atomic carbon :C: - The source of light is the electrical arcing between two carbon
rods. Liquid nitrogen cools the reaction vessel. The black substance is soot. This photo was
taken in the Laboratory of Professor Phil Shevlin at Auburn University.
43
Carbon nanofoam
• Carbon nanofoam is the
fifth known allotrope of
carbon
• discovered in 1997 by
Andrei V. Rode and coworkers at the Australian
National University in
Canberra.
44
Carbon nanofoam
• It consists of a low-density cluster-assembly of
carbon atoms strung together in a loose threedimensional web.
– Each cluster
• is about 6 nm wide
• consists of about 4000 carbon atoms linked in graphite-like
sheets that are given negative curvature by the inclusion of
heptagons among the regular hexagonal pattern.
• This is the opposite of what happens in the case
of buckminsterfullerenes, in which carbon sheets
are given positive curvature by the inclusion of
pentagons.
45
A video on YouTube on a discussion of carbon
allotropes - including diamond, lonsdaleite, graphite,
and the fullerenes.
http://www.youtube.com/watch?v=vYkyUqUa
6vU
46
A video on a module on Allotropy
http://www.youtube.com/watch?v=n22_6pCX
6e0
47
A Comic Strip on Allotropes
48
References
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
http://www.increasemyvocabulary.com/definition/of/allotropy/
http://en.wikipedia.org/wiki/Allotropes_of_carbon
http://en.wikipedia.org/wiki/Diamond
http://en.wikipedia.org/wiki/Allotropes
http://www.increasemyvocabulary.com/definition/of/allotrope/
http://www.ausetute.com.au/allotropy.html
http://www.webelements.com/
http://simple.wikipedia.org/wiki/Allotropes
http://simple.wikipedia.org/wiki/Graphite
http://simple.wikipedia.org/wiki/Diamond
http://en.wikipedia.org/wiki/Lonsdaleite
http://en.wikipedia.org/wiki/Graphene
http://en.wikipedia.org/wiki/Amorphous_carbon
http://en.wikipedia.org/wiki/Buckminsterfullerene
http://en.wikipedia.org/wiki/Glassy_carbon
http://www.toondoo.com
49
50