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Carbon is an element that is the found in abundance in the earth's crust. It is found in
group 14 of the Periodic Table and has the atomic number 6. Carbon, which is non
metallic in nature, is the 4th most abundant element in the universe and the 1th most
abundant element in the !arth's crust. Carbon is such an important element that an
entirel" separate field of chemistr" is devoted to this element and its compounds.
#rganic chemistr" is the stud" of carbon compounds.
How carbon was discovered
$umans have been aware of carbon since the earliest of times. %hen cave peoplemade a fire, the" saw smo&e form. The blac& color of smo&e is caused b" unburned
spec&s of carbon. The smo&e ma" have collected on the ceiling of their caves as soot.
ater, when lamps were invented, people used oil as a fuel. %hen oil burns, carbon
is released in the reaction, forming a soot" covering on the inside of the lamp. That
form of carbon became &nown as lampblac&. ampblac& was also often mi(ed with
olive oil or balsam gum to ma&e in&. )nd ancient !g"ptians sometimes used
lampblac& as e"eliner.
#ne of the most common forms of carbon is charcoal. Charcoal is made b" heating
wood in the absence of air so it does not catch fire. Instead, it gives off water vapor,
leaving pure carbon. This method for producing charcoal was &nown as earl" as the
*oman civili+ation - /.C.0).. 4263.
rench ph"sicist *en5 )ntoine Ferchault Reaumur (1683-1757) believed carbon
might be an element. $e studied the differences between wrought iron, cast iron, and
steel. The main difference among these materials, he said, was the presence of a
blac& combustible material that he &new was present in charcoal.
Carbon was officiall" classified as an element near the end of the eighteenth
centur". In 1272, four rench chemists wrote a boo& outlining a method for naming
chemical substances. The name the" used, carbone, is based on the earlier atin term
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for charcoal, charbon.
Coal, soot nearl" pure carbon3, and diamonds are all nearl" pure forms of carbon.
Isotopes
Carbon e(ists in three naturall"0occurring isotopes 8 carbon019, carbon01:, and
carbon014; the numbers refer to their atomic weights. The different &inds of carbon
have ver" similar but not <uite identical3 chemical and mechanical properties; the
main practical significance of the e(istence of different isotopes stems from the fact
that carbon014 is radioactive, with a half0life of a few thousand "ears. This is what
ma&es carbon dating possible 8 C014 is thought to be created b" impacts from cosmic
ra"s at around the same rate it disappears through radioactive deca", so the ratio of the
isotopes in the environment should sta" more or less constant. iving organisms
constantl" e(change carbon with their environment until the da" the" die 8 so if we
find a s&ull with onl" half as much C014 in it as we see in our environment, we can
infer that its owner died one half0life of C014 ago 8 that=s about ,6-- "ears. The
techni<ue is e(tremel" useful in archaeolog", but it is hard to &now <uite how
accurate it is 8 the assumption that C014 levels in the atmosphere have remained
appro(imatel" constant is a difficult one to test.
3.0 Properties to their usage in everyday life as is in industry
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3.1 How carbon is essential to life
>ost living things on !arth are made of carbon. iving things need carbon in order
to live, grow, and reproduce. Carbon is a finite resource that c"cles through the !arth
in man" forms. This ma&es carbon available to living organisms and remains in
balance with other chemical reactions in the atmosphere and in bodies of water li&e
ponds and oceans.
In its metabolism of food and respiration, an animal consumes glucose C6$19#63,
which combines with o("gen #93 to produce carbon dio(ide C#93, water $9#3,and energ", which is given off as heat. The animal has no need for the carbon dio(ide
and releases it into the atmosphere. ) plant, on the other hand, uses the opposite
reaction of an animal through photos"nthesis. It inta&es carbon dio(ide, water, and
energ" from sunlight to ma&e its own glucose and o("gen gas. The glucose is used for
chemical energ", which the plant metaboli+es in a similar wa" to an animal. The plant
then emits the remaining o("gen into the environment.
Cells are made of man" comple( molecules called macromolecules, which include
proteins, nucleic acids *?) and ?)3, carboh"drates, and lipids. The
macromolecules are a subset of organic molecules an" carbon0containing li<uid,
solid, or gas3 that are especiall" important for life. The fundamental component for all
of these macromolecules is carbon. The carbon atom has uni<ue properties that allow
it to form covalent bonds to as man" as four different atoms, ma&ing this versatile
element ideal to serve as the basic structural component, or bac&bone, of the
macromolecules.
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Diamond
iamonds are formed inside the earth under the conditions of high temperature
about 1--oC3 and high pressure about 2-,--- atmospheres3. In a diamond cr"stal,
each carbon atom is lin&ed to four other carbon atoms b" covalent bonds in a
tetrahedral fashion. This results in a three dimensional arrangement as shown in Fig.
!.1
Fig. 28.1 Three dimensional networ o! car"on atoms in diamond
The three0diamensional networ& of covalentl" bonded carbon atoms provides a
rigid structure to diamonds. This rigidit" ma&es diamond a ver" hard substance.
It is, in fact, the hardest natural substance &nown. The onl" other substance harder
than diamond is silicon carbide which is also &nown as carborandum but note that
diamond is a natural substance whereas carborandum is a s"nthetic one.
iamonds are basicall" colourless. $owever, some impurities impart colour to
them.
The densit" of diamond is high. It has a value of :.1 g cm8:. The melting point
of diamond in vacuum3 is also ver" high, i.e. :--oC because a large amount of
heat energ" is re<uired to brea& the three0dimensional networ& of covalent bonds.
@ince all the four electrons are covalentl" bonded and there are no free electrons in
diamond, hence it does not conduct electricit". /ut diamond is a good conductor of
heat. Its thermal conductivit" is five times that of copper. Thus, it can easil"
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dissipate the heat energ" released b" friction when it is used as an abrasive.
/ecause of its above0mentioned properties, diamond has the following usesA
i3 It is used in cutting and grinding of other hard materials.
ii3 It is also emplo"ed in instruments used for cutting of glass and drilling of
roc&s.
iii3 It is used in Beweller". /eautiful ornaments are made with diamonds. The
high refractive inde( of diamond 9.3 ma&es it ver" brilliant when it is
properl" cut and polished.
"raphite
In contrast to diamond, graphite is soft, blac& and slipper" solid. It has a metallic
luster. It is also a good conductor of electricit" and heat.
/oth graphite and diamond contain onl" carbon atoms, then wh" do the" e(hibit
such different properties %e can find an answer to this <uestion if we loo& at the
structure of graphite as given below in ig.97.9.
Covalent bond Carbon atom
#tructure of Diamond #tructure of "raphite
Fig.28.2 #tructures o! $iamond and gra%hite
carbon atoms
wea$ binding forces
%ovalentbond