By PRAGYANSHARMA POLAVARAPU (Vrs.Somanchi)
In the old days 55 years ago I
vaguely remember there was a list of 92 elements (the very interesting
Mendeleev Periodic Table) .
The Trans-uranium
elements subsequently included in the Periodic Table have increased the number of elements to 118 . But the transuranium elements are mostly unstable radioactive elements and are created in laboratories or in nuclear reactors and
particle accelerators . But being a simple
worshipper of old Daltonian chemistry I am not interested.
*****
Out of the old periodic table list of
92 elements 17 are non metals .Here I am concerned only with the
old familiar non-metals like C, H2, N2 and O2 ,S –all
of which are important in organic chemistry. A few words about non-metals
in general.
While metals have a special
metallic shine and and conduct heat and electricity easily,the solid
non-metallic elements — carbon, sulphur, phosphorous, silicon, boron
etc.— are brittle, do not bend and do not possess the mirror like shine of
metal.( Bromine is a liquid non-metal).
The gases oxygen, nitrogen, hydrogen,
chlorine, etc are treated as non-metals because their
chemical reactions are identical with the reactions of the solid non
metals.(Hydrogen is sometimes treated as metal and sometimes as non-metal based
on its chemical properties).
Even scientists thought till 300 or
400 years ago that pure unpolluted air was an element. But it was found that
air is a mechanical mixture of oxygen ( 21% ) and nitrogen (
78%).Water too was treated as an element but when electrolyzed broke into
the two elemental gases oxygen and hydrogen. It is a chemical compound.
*****
Everybody knows that elements,
whether metals or nonmetals, are composed of extremely minute
unbreakable particles called atoms. The sharp point of a pin can
accommodate thousands of millions of atoms! (The correct number is many times
more) .There are now 118 elements and so 118 types of atoms
.But we are now interested only in the first 92 elements of the old Mandeliev
periodic table.
The smallest particles of a
chemical compound is the molecule. Molecules are groups of
atoms strongly tied by bonds made of electron pairs . In another
way we may say that molecules are just like boxes in which atoms are
fixed rigidly in a 3D structure.
Understanding Organic Reactions
After two or three centuries of
modern research scientists could realize that the slow organic chemical
reactions in bodies of humans,plants, fishes,animals are entirely similar in
nature to the inorganic chemical reactions in mineral substances. Only
the rates(speeds) of the reactions are different. Inorganic chemical
reactions are generally instantaneous while the organic chemical reactions take
hours or even a day to complete.
Even in modern age scientists
thought for a long time that a “vital force”( un-understandable strange force)
manages the organic reactions and that the organic reactions cannot be
explained by rules of inorganic chemistry. Scientists are now
agreed that inorganic and organic reactions are completely similar
and that there is no need for any vital force. Of course there are vast
differences in the way inorganic and organic chemical reactions proceed.
(1) In molecules of mineral
substances (inorganic substances) only very few atoms , at the most
ten atoms, exist in participating or resultant molecules . But in the world of
organic chemistry a molecule( participating molecule or
resultant molecule) may contain hundreds of atoms !
(2)Almost every molecule in
chemical reactions in living beings should contain atoms of element carbon.
Reason is that all organic chemical compounds are created based on
“hydrocarbons” which contain a long chain of carbon atoms to which a
large number of hydrogen atoms are attached
(3) The inorganic
chemical reaction is instantaneous but the chemical reactions on organic
substances proceed very slowly taking hours or even a day or more.
(4) There are said to be around
20 million “organic chemical compounds” classified and studied in science
laboratories. In comparison the inorganic compounds classified in science
laboratories are only about half a million i.e. around 500,000.
Organic chemical reactions
Here we study organic chemical
reactions in a few special situations
(a) Abundance of water
On planet earth the most
important and extensive thing is water –mainly the ocean water. For
nearly two to three billion years only single celled organisms lived in water .
Only after the atmosphere was filled with oxygen and only after plants prepared
carbohydrate food living creatures migrated to land surface away
from water.
( b) Abundance of air
Scientists say that in the oldest
atmosphere of earth 4500 billion years ago(when earth was a burning ball of
melted rocks and melted metal) there were only helium and hydrogen in air .
There was no oxygen. This was the “first atmosphere” of earth .
The earth started to cool
quickly after it moved very far away from sun and entered its orbit in
extremely cold cosmic space. Thick semi-solid stony plates of continent-size
and above them a solid crust formed on earth. The temperature
was around 70 to 80 degrees in the oceans . It might have rained
for hundreds of years. There were thousands of volcanoes.There was
pungent and suffocating atmosphere. It was called “second atmosphere”.
Scientists say that after several
hundred millions later the temperatures further came down to 30 to 40 degrees
. Green cyanobacteria containing chlorophyll started manufacturing
carbohydrate during sunlight hours and also released oxygen in to
atmosphere for a billion years or more . The great “oxygen atmosphere” the life
giver was created and modern species very slowly developed in the long
millions of years. This is called “third atmosphere” of planet earth.
(c) The oxygen reaction region called
fire
All substances like petroleum and
diesel, vegetable oils,and things like paper,wood,dry
leaves,cotton,seeds,sugar are all hydrocarbon based substances. Even a
burning candle,burning paper,burning match stick etc have a temperature
of 1500degrees and can burn any hydrocarbon substance. Most fires on earth
relate to hydrocarbon burning only. In every fire involving hydrocarbons ,water
vapour and carbon dioxide gas are formed with release of great amounts of
heat energy.
(d) In presence of sunlight and
lightnings — The sunlight and lightning are always present at some area
of the sphere of earth —whether on land or on ocean surface or in a deep
forest. Photosynthesis by plants(whether on land or in sea) is entirely
dependent on sunlight as sun is the supplier of energy. The lightnings
help produce lot of nitrogenous fertilized in soil.
( d ) The slow organic reaction
While the reactions in
inorganic chemistry are completed in seconds , the organic metabolic
reactions occurring inside living creatures are so slow that
they may take hours or even a day or more for completion of
reaction. Respiration, digestion, fermentation for alcohol, formation of curd
from milk, ripening of fruit and even putrefaction —all are combinations of
hundreds of organic chemical reactions.
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