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Structure
and bonding (Part 3)
Francine
Taylor-Campbell, Contributor
What
is allotrophy?
Allotrophy
is the ability of an element to exist
in the same physical state but in
different structural forms. This causes
them to have different physical properties
but the same chemical properties
How
are the atoms in graphite, diamond
and sodium chloride arranged?
Diamond
and graphite are giant molecular or
macromolecular crystals. A diamond
consists of carbon atoms tetrahedrally
arranged and bonded by strong covalent
bonds. A graphite consists of carbon
atoms arranged in hexagonal rings
and in layers, while sodium chloride
is an ionic solid having a giant structure.
What
are the main differences in bonding
between diamond and graphite?
In
diamond, four carbon atoms are joined
in a tetrahedral arrangement. This
is repeated throughout to give a three-dimensional
structure with strong, covalent bonds.
In
a graphite, each carbon atom is bonded
to three other atoms, arranged hexagonally
in layers. These layers are held together
by weak bonds which enable them to
slide over one another. There are
strong, covalent bonds, however, between
the carbon atoms in each layer. Note
that, for graphite, since the carbon
atom is bonded to only three others,
it means that each carbon atom has
a fourth electron not involved in
bonding. That is a free mobile electron.
This will influence the properties
of graphite.
What
are diamond and graphite allotropes?
Graphite
and diamond are composed of carbon
atoms but their structures are different,
hence, these solids are allotropes.
They show the same chemical properties,
since they have the same element -
carbon, but the difference in their
structure causes them to have different
chemical properties.
How
do the properties of sodium chloride,
graphite and diamond differ?
| Property |
Sodium
Chloride |
Diamond |
Graphite |
| Apperance |
Crystalline
solid |
Sparkling
solid |
Dark
solid |
| Hardness |
Brittle
- easily split |
Very
hard - due to strong convalent
bonds in the structure |
Soft
and flaky - due th eweak bonds
between the layers. Layers can
slip over each other hence it
is a good lubricant. |
| Melting
point |
High
due to strong ionic bonds that
need a lot of energy to break |
Very
high due to strong covalent bonds
that need vast amounts of energy
to break. |
Very
high due to strong covalent bonds
that are difficult ot break |
| Electrical
Conductivity |
Conducts
electricity when dissolved in
solution or when molten as the
ions are free to move. |
Cannot
conduct electricity because all
electrons are involved in bonding
hence there are no free electrons
to carry a current. |
Conducts
electricity when solid as mobile
electrons are present |
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Dr
Paul Aiken demonstrates the
use of the oscilloscope with
the LPM to a class of students.
- FILE
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Francine
Taylor-Campbell is an independent
contributor.
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