The Periodic Table
A periodic table is a tabular display of the chemical
elements, organized on the basis of their atomic numbers, electron
configurations, and recurring chemical properties. Elements are presented in
order of increasing atomic number (number of protons). The standard form of
table comprises an 18 × 7 grid or main body of elements, positioned above a
smaller double row of elements. The table can also be deconstructed into four
rectangular blocks: the s-block to the left, the p-block to the right, the
d-block in the middle, and the f-block below that. The rows of the table are
called periods; the columns of the s-, d-, and p-blocks are called groups, with
some of these having names such as the halogens or the noble gases. Since, by
definition, a periodic table incorporates recurring trends, any such table can
be used to derive relationships between the properties of the elements and
predict the properties of new, yet to be discovered or synthesized, elements.
As a result, a periodic table—whether in the standard form or some other
variant—provides a useful framework for analyzing chemical behavior, and such
tables are widely used in chemistry and other sciences.
Although precursors exist, Dmitri Mendeleev is generally
credited with the publication, in 1869, of the first widely recognized periodic
table. He developed his table to illustrate periodic trends in the properties
of the then-known elements. Mendeleev also predicted some properties of
then-unknown elements that would be expected to fill gaps in this table. Most
of his predictions were proved correct when the elements in question were
subsequently discovered. Mendeleev's periodic table has since been expanded and
refined with the discovery or synthesis of further new elements and the
development of new theoretical models to explain chemical behaviour.
Download a copy here.
http://en.wikipedia.org/wiki/Periodic_table
http://iupac.org/
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