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 57 to 71
are known as lanthanide or rare earth elements.
These elements are found on earth in only very small amounts.
Elements 89 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.
