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Module 1: La tabla periódica: una visión general de la química

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XSIQ
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Chemistry - Mendeleev

Mendeleev

Dimitri Mendeleev is the scientist most commonly discussed when reviewing
the history of the development of the periodic table. He spent years
collecting and sorting information about the elements and summarised this
on cards (one for each element), which he arranged on the walls on his
laboratory. Eventually he established a logical order and stated the first
periodic law:

Mendeleev arranged the elements into according to and into according to
His periodic table was constructed (on the walls of his laboratory) in such
a way that gaps were left where the pattern would otherwise be destroyed.
He predicted the properties of these 'yet to be discovered' elements
(particularly Sc, Ga and, Ge) very accurately, based on the properties
shown by other elements in the groups where he left spaces for these
elements.

placed particular importance on chemical properties. Iodine had a
smaller atomic weight (126.90) than tellurium (127.60) so arranging the
elements in order of would put. Mendeleev observed that this would put
both elements 'out of sync' with the other elements in their groups as far
as chemical properties were concerned. However, when he placed Te before I,
suggesting errors in atomic weights, the trends in properties were
restored. The astuteness of Mendeleev's thinking was revealed many years
later when the periodic behaviour of elements was attributed to electron
arrangement and the elements arranged in order of (established by Moseley
in 1914) - in which instance comes naturally The higher atomic weight (now
relative atomic mass) of Te can be attributed to the range of isotopes
present in a naturally-occurring sample.

The key features of Mendeleev's periodic table may be summarised as:

* elements arranged in order of

* elements with similar chemical properties placed into vertical

* horizontal rows called

* gaps left for the properties of these elements were predicted

Published in 1871, some 40 years before Rutherford proposed the nuclear
model of the atom, Mendeleev's periodic table played a significant role in
the discovery of atomic structure.

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