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Periodic Table first discovered in 1869 by Dmitry I. Mendeleyev is a way
of presenting all the elements so as to show their similarities and
differences. The elements are arranged in increasing order of atomic
number(Z) as you go from left to right accross the table. The
horizontal rows a called periods and the vertical rows,
groups.
A noble gas is found at the right hand side of each period. There
is a progression from metals to non-metals across each period. Elements
found in groups (e.g. alkali, halogens) have a similar electronic
configuration. The number of electrons in outer shell is the same as the
number of the group (e.g. lithium 2�1).
The block of elements between groups II and III are called transition
metals. These are similar in many ways; they produce colored
compounds, have variable valency and are often used as catalysts.
Elements 58 to 71 are known as lanthanide or rare earth elements.
These elements are found on earth in only very small amounts.
Elements 90 to 103 are known as the actinide elements. They include most
of the will known elements which are found in nuclear reactions.
The elements with larger atomic numbers than 92 do not occur naturally.
They have all been produced artificially by bombarding other elements
with particles.
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