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Dalton's theory was based on that the atoms of different elements could be distinguished by differences in their weights.
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John Newlands divided the than discovered 56 elements into 11 groups, based on characteristics.
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Dimitri Mendeleev started the development of the periodic table, arranging chemical elements by atomic mass. He predicted the discovery of other elements, and left spaces open in his periodic table for them.
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Antoine Bequerel first discovered radioactivity.
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William Ramsay and Rayleigh discovered the noble gases, which were added to the periodic table as group 0.
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Thomson interpreted the deflection of the rays by electrically charged plates and magnets as evidence of "bodies much smaller than atoms" that he calculated as having a very large value for the charge-to-mass ratio
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Earnest Rutherfords theory was describing the atom as having a central positive nucleus surrounded by negative orbiting electrons.
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Neil described the way atoms emit radiation by suggesting that when an electron jumps from an outer orbit to an inner one
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James Chadwick first discovered neutrons, and isotopes were identified. This was the complete basis for the periodic table
