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In 1809 at least 47 elements were discovered
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1863 English chemist John Newlands divided the than discovered 56 elements into 11 groups
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1869 Russian chemist Dimitri Mendeleev started the development of the periodic table
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1894 Sir William Ramsay and Lord Rayleigh discovered the noble gases
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In 1903 Rutherford announced that radioactivity is caused by the breakdown of atoms.
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1914 Rutherford first identified protons in the atomic nucleus