Carbon

Carbon, an element discovered before history itself, is one
of the most abundant elements in the universe. It can be
found in the sun, the stars, comets, and the atmospheres of
most planets. There are close to ten million known carbon
compounds, many thousands of which are vital to the basis
of life itself (WWW 1). 

Carbon occurs in many forms in nature. One of its purest
forms is diamond. Diamond is the hardest substance known on
earth. Although diamonds found in nature are colorless and
transparent, when combined with other elements its color
can range from pastels to black. Diamond is a poor
conductor of heat and electricity. Until 1955 the only
sources of diamond were found in deposits of volcanic
origin. Since then, scientists have found ways to make
diamond from graphite and other synthetic materials.
Diamonds of true gem quality are not made in this way
(Beggott 3-4). 

Graphite is another form of carbon. It occurs as a mineral
in nature, but it can be made artificially from amorphous
carbon. One of the main uses for graphite is for its
lubricating qualities. Another is for the "lead" in
pencils. Graphite is used as a heat resistant material and
an electricity conductor. It is also used in nuclear
reactors as a lubricator (Kinoshita 119-127). 

Amorphous carbon is a deep black powder that occurs in
nature as a component of coal. It may be obtained
artificially from almost any organic substance by heating
the substance to very high temperatures without air. Using
this method, coke is produced from coal, and charcoal is
produced from wood. Amorphous carbon is the most reactive
form of carbon. Because amorphous carbon burns easily in
air, it is used as a combustion fuel. The most important
uses for amorphous carbon are as a filler for rubber and as
a black pigment in paint (WWW 2). 

There are two kinds of carbon compounds; inorganic and
organic. Inorganic compounds are binary compounds of carbon
with metals or metal carbides. They have properties ranging
from reactive and saltlike; found in metals such as sodium,
magnesium, and aluminum, to an unreactive and metallic,
such as titanium and niobium (Beggott 4). 

Carbon compounds containing nonmetals are usually gases or
liquids with low boiling points. Carbon monoxide, a gas, is
odorless, colorless, and tasteless. It forms during the
incomplete combustion of carbon (Kinoshita 215-223). It is
highly toxic to animals because it inhibits the transport
of oxygen in the blood by hemoglobin (WWW 2). Carbon
dioxide is a colorless, almost odorless gas that is formed
by the combustion of carbon. It is a product that results
from respiration in most living organisms and is used by
plants as a source of carbon. Frozen carbon dioxide, known
as dry ice, is used as a refrigerant. Fluorocarbons, such
as Freon, are used as refrigerants (Kinoshita 225-226). 

Organic compounds are those compounds that occur in nature.
The simplest organic compounds consist of only carbon and
hydrogen, the hydrocarbons. The state of matter for organic
compounds depends on how many carbons are contained in it.
If a compound has up to four carbons it is a gas, if it has
up to 20 carbons it is a liquid, and if it has more than 20
carbons it is a solid (Kinoshita 230-237).The carbon cycle
is the system of biological and chemical processes that
make carbon available to living things for use in tissue
building and energy release (Kinoshita 242). 

All living cells are composed of proteins consisting of
carbon, hydrogen, oxygen, and nitrogen in various
combinations, and each living organism puts these elements
together according to its own genetic code. To do this the
organism must have these available in special compounds
built around carbon. These special compounds are produced
only by plants, by the process of photosynthesis.
Photosynthesis is a process in which chlorophyll traps and
uses energy from the sun in the form of light. Six
molecules of carbon dioxide combine with six molecules of
water to form one molecule of glucose (sugar). The glucose
molecule consists of six atoms of carbon, twelve of
hydrogen, and six of oxygen. Six oxygen molecules,
consisting of two oxygen atoms each, are also produced and
are discharged into the atmosphere unless the plant needs
energy to live. In that case, the oxygen combines with the
glucose immediately, releasing six molecules of carbon
dioxide and six of water for each molecule of glucose
(Beggott 25-32). The carbon cycle is then completed as the
plant obtains the energy that was stored by the glucose. 

The length of time required to complete the cycle varies.
In plants without an immediate need for energy, the
chemical processes continue in a variety of ways. By
reducing the hydrogen and oxygen content of most of the
sugar molecules by one water molecule and combining them to
form large molecules, plants produce substances such as
starch, inulin , and fats and store them for future use.
Regardless of whether the stored food is used later by the
plant or consumed by some other organism, the molecules
will ultimately be digested and oxidized, and carbon
dioxide and water will be discharged.Other molecules of
sugar undergo a series of chemical changes and are finally
combined with nitrogen compounds to form protein
substances, which are then used to build tissues (WWW 2). 

Although protein substances may pass from organism to
organism, eventually these too are oxidized and form carbon
dioxide and water as cells wear out and are broken down, or
as the organisms die. In either case, a new set of
organisms, ranging from fungi to the large scavengers, use
the waste products or tissues for food, digesting and
oxidizing the substances for energy release (WWW 1). 

At various times in the Earth's history, some plant and
animal tissues have been protected by erosion and
sedimentation from the natural agents of decomposition and
converted into substances such as peat, lignite, petroleum,
and coal. The carbon cycle, temporarily interrupted in this
manner, is completed as fuels are burned, and carbon
dioxide and water are again added to the atmosphere for
reuse by living things, and the solar energy stored by
photosynthesis ages ago is released (Kinoshita 273-275). 

Almost everything around us today has some connection with
carbon or a carbon compound. Carbon is in every living
organism. Without carbon life would not exist as we know it.
 
Works Cited:
 
1. Beggott, Jim Great Balls of Carbon New Scientist, July
6, 1991.
 
2. Kinoshita, Kim Carbon Compounds Random, New York 119-275
(1987). 

3. WWW Carbon http://www.usc.edu/chem/carbon.html 1995. 

4. WWW Carbon Compounds
http://www.harvard/deots/chen/carbon.html 1995.