Chemistry - Frederick Soddy
In 1910, Soddy suggested that the experimentally observed fact that all
atoms of an element had the same chemical properties did not mean that
atoms of the same element could not have different masses.
This astute observation was to lead to a solution to the mystery of
apparently new elements produced by radioactive decay without enough places
in the periodic table to accommodate these elements.
It was eventually realised that many of these 'new' elements had chemical
properties that were the same as well-known elements but with some
differences in physical properties.
Soddy suggested that a chemical element could be seen as both a pure
substance and a mixture. A pure substance in the sense that all atoms of
the element had the same chemical properties but a mixture in the sense
that atoms of the same element may differ in mass and in radioactive
behaviour. Since these different atoms of the same element belonged in the
same place in the periodic table, Soddy called them isotopes (from the
Greek_ isos,_ equal, and _topos,_ place).
The cause of the different masses of isotopes of the same element was
eventually solved when James Chadwick discovered the neutron in 1932.
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