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SSC
CHEMISTRY
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Classification of
elements
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Introduction
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During the 4th century B.C.,
ancient Greek philosophers like Aristotle
believed that all forms of matters were made up
of just four elements arranged in different
proportions. These were air (aer), water
(aqua), fire (ignis) and earth
(terra). Now we know that there are
nearly 118 elements, out of which only 90 occur
naturally on earth. The Lawrence Berkeley
National Laboratory in California discovered the
118th element recently by bombarding
targets of lead with high energy krypton ions. 28
artificial elements have been made in
laboratories. These exist only for a few
millionths of a second!
The simplest element, hydrogen, was the first to
form shortly after the Big Bang (which created
the universe thousands of millions of years
ago). It was followed by helium. All elements
that make up the earth today were created in the
heart of giant stars. When these stars exploded,
the elements were scattered through space.
Before the 18th century, only 10
elements were known and it was only in the
18th and 19th centuries
that most of the other elements were
discovered.
With the discovery of a large number of
elements, scientists felt the need for some
simple method to classify their compounds. After
numerous attempts, scientists were ultimately
successful in arranging the elements in such a
way that similar elements were grouped together
(notably by Dobereiner in 1822, Newland in 1886
and Lothar Meyer in 1870). This arrangement of
elements is known as 'classification of
elements'. Later Dmitri Mendeleev's
classification of elements led to the formation
of the periodic table, which was indeed one of
the greatest milestones in the development of
chemistry. The earlier attempts by scientists
failed because their method could only cover a
limited range of elements, but Mendeleev's
classification covered all the 63 elements known
at that time.
Just as the classification of plant and animal
kingdom in biology helps us to learn more
precisely and successfully about a wide range of
species of plants and animals, the classification
of elements helps us to learn and understand the
properties of a large number of elements by
studying only a few prototypes from each
group. |
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