Carbon.
Carbon is unique in
its chemical properties
because it forms a
number ofcomponents
superior than the total
addition of all the other
elements in combination
with each other.
The biggest group of all these components is the one
formed by carbon andhydrogen.
We know a minimum of about
1 million organic components
and this number increases
rapidly every year.
Althoughthe classification
is not strict, carbon forms
another series of compounds
considered as inorganic,
in a muchlower number
than that of the organic compounds.Elemental
carbon exists in two
well-defined allotropic
crystallineforms: diamond andgraphite. Other forms with little crystallinity are vegetal carbon and black fume.
Chemically pure carbon can
be prepared by termic
decomposition of
sugar (sucrose)
in absence of air.
The physical and chemical
properties of carbon
depend on the crystalline
structure of the element.
Its density fluctuates from
2.25 g/cm³ (1.30 ounces/in³)
for graphite and 3.51 g/cm³ (2.03 ounces/in³) for diamond.
The melting point of graphite
is 3500ºC (6332ºF)
and the extrapolated boiling
pointis 4830ºC (8726ºF).
Elemental carbon is aninert
substance, insoluble in water,
diluted acids and bases,
as well as organic solvents.
At high temperatures it
binds with oxygen to
form carbon monoxide
or dioxide. With hot
oxidizing agents,
like nitric acid and
potassium nitrate,
metilic acid C6(CO2H)6is obtained.
Among the halogens only
fluorine reacts with elemental
carbon.
A high number
of metalscombine with
the element at high
temperatures to form
carbides.It forms three
gaseous components
with
theoxygen: carbon monoxide,
CO,
carbon dioxide,
CO2, and
carbon suboxide,
C3O2.
The two first ones are
the most important
from the industrial
point of view.
Carbon forms compounds
with the halogens
with CX4as general
formula,
where X isfluorine,
chlorine,
bromineoriodine.
At ambient temperature
carbon tetrafluoride is
gas, tetrachloride
is liquid and the other
two compounds are solids.
We also know mixed
carbon tetrahalides.
The most important of all
may be the dichlorodifluoromethane, CCl2F2, called freon.
Carbon in the environmentCarbon
and its components are
widely distributed
in nature.
The estimation is thatcarbon
forms 0,032% of The Earth’s crust.
Free carbon is found in big
reservoirs like hard coal,
amorphous form
of the element with
other complex compounds
of carbon-hydrogen-nitrogen.
Pure crystalline carbonis
found in the form of graphite and diamond.The Earth's atmosphere contains an ever-increasing concentration of carbon
dioxide and carbon
monoxide, form fossil
fuel burning, and of
methane (CH4), form
paddy fields and cows.
No element is more
essential to life than
carbon, because only
carbon forms strong
single bonds to itself
that are stable enough
to resist chemical
attack under ambient conditions.
This give carbon the ability
to form long chains and
rings of atoms, which
are the structural basis
for many compounds
that comprise the living
cell, of which the most
important is DNA.
Big quantities of carbon
are found in the form
of compounds.
Carbon is present in
the atmosphere as
carbon dioxide in 0,03%in volume.
Several minerals, like
limestone,
dolomite,
gypsum and marble,
containcarbonates.
All the plants and live animals
are formed by complex organic compounds where carbon is
combined with hydrogen,
oxygen,
nitrogenand
other elements.
The remains of live plants
and animals form
deposits: of petroleum,
asphalt and bitumen.
The natural gas deposits
contain compounds formed
by carbon and hydrogen.
ApplicationThe free element
has a lot of uses,
including decoration
purposes of diamonds
in jewelry or black fume
pigmentin automobile’s rims and printer’s ink.
Another carbon form,
the graphite, is used for
high temperature crucibles,
dry cell and light arch electrodes,
for pencil tips and as
a lubricant.
Vegetal carbon, an amorphous
form of carbon, is used as
gas absorbent and bleaching agent.Carbon compounds
have plenty of uses.
Carbon dioxide is used in drinks carbonatation, in fire
extinguishers and, in solid state, as a cooler (dry ice).
Carbon monoxide is used
as reduction agent in
many metallurgic processes.
Carbon tetrachloride and carbon disulphide are important
industrial solvents.
Freon is used in cooling systems.Calciumcarbide
is used to prepare acetylene;
it’s used for welding and
cutting metals, as well
as for preparation of other
organic compounds.
Other metallic carbides
have important uses as
heat-resistants and metal
cutters.
Health effects of carbon
Elemental carbon is of very
low toxicity.
Health hazard data
presented here is
basedon exposures
to carbon black, not
elemental carbon.
Chronic inhalation exposure
to carbon black may
result in temporary
or permanent damage
to lungs and heart.
Pneumoconiosis has been
found in workers engaged in the production of carbon black. Skin conditions such as inflammation
of the hair follicles,
and oral mucosal lesions
have also been reported
from skin exposure.
Carcinogenicity- Carbon black
has been listed by the International Agency for Research on
Cancer (IARC) within Group 3
(The agent is not classifiable as
to its carcinogenicity to humans).
Some simple carbon compound
can be very toxic, such as
carbon monoxide (CO) or
cyanide (CN-).Carbon
14 is one of the radionuclides
involved in atmospheric
testing of nuclear weapons,
which began in 1945, with a
US test, and ended in 1980
with a Chinese test.It is among
the long-lived radionuclides
that have produced and will
continue to produce increased
cancers risk for decades and
centuries to come. It also can
cross the placenta, become
organically bound in developing
cells and hence endanger fetuses.
Most we eat is made up of
compounds of carbon,
giving a total carbon intake og 300 g/day.
Digestion consist of
breaking these compounds
down into molecules than
can be adsorbed to the
wall of the stomach or intestine.
There they are trasported by
the blood to sites where they
are utilized or oxidised to
release the energy they contain.
Environmental effects of carbonNo negative environmental effects have been reported.Graphite Diamonds
