329Carbon-Allotrope
Carbon is ordinarily classified as a nonmetal although it has some metallic properties and
is occasionally classified as a metalloid. Where applicable, properties listed below are for
hexagonal graphitic carbon, the most thermodynamically stable form of carbon under
ambient conditions.
In terms of the Metallic
Character of Carbon:
It has a lustrous
appearance.
It shows good electrical
conductivity.
It has a positive
temperature coefficient of
electrical resistivity, in the
direction of its planes, that
is, its conductivity
decreases with increasing
temperature (behaving in
this way as a metal).
It has the electronic band
structure of a semimetal.
The various allotropes of
carbon, including graphite,
are capable of accepting foreign atoms or compounds into their structures via
substitution, intercalation or doping (interstitial or intrastitial) with the resulting
materials being referred to as 'carbon alloys'.
It can form ionic salts, including a sulphate, perchlorate, nitrate, hydrogen selenate,
and hydrogen phosphate.
In organic chemistry, carbon can form complex cations—termed carbocations—in
which the positive charge is on the carbon atom; examples are CH+ 3, CH+ 5, and
their derivatives.
In terms of the Nonmetallic Character of Carbon:
It is brittle.
It behaves as a semiconductor, perpendicular to the direction of its planes.
Most of its chemistry is nonmetallic.
It has relatively high ionization energy.
It has a relatively high electronegativity, compared to most metals.
Its oxide CO 2 forms a medium-strength carbonic acid H 2 CO 3.
Carbon Filtering
Carbon filtering is a method of filtering that uses a piece of activated carbon to remove
contaminants and impurities, utilizing chemical adsorption.
Each piece of carbon is designed to provide a large section of surface area, in order to
allow contaminants, the most possible exposure to the filter media. One pound (450 g) of
activated carbon contains a surface area of approximately 100 acres (40 Hectares). This
carbon is generally activated with a positive charge and is designed to attract negatively