Periodic Table By Gmancilla Sep 25, 1669 The discovery of Phosphorus Sep 25, 1869 Dmitri Mendeleev early development of the Periodic Table Sep 25, 1886 Antoine Becquerel discovered radioactivity Sep 25, 1897 J. J. Thomson discovered electrons Sep 25, 1903 Rutherford discovered that radioactivity is the cause of the breakdown of atoms Sep 25, 1911 Rutherford and Hans Geiger discovered that electrons orbit the nucleus of an atom. Sep 25, 1932 James Chadwick first discovered neutrons and isotopes were identified. Sep 25, 1932 Cockroft and Walton first split an atom.
