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