Periodic Table By declanguilfoyle1 Jan 1, 1649 Phosphorus Discovered Jan 1, 1829 Halogen Triad and Alkali metal Triad discovered Feb 17, 1862 First Periodic Table invented Jan 1, 1869 Dimitriv Mendeleev published his periodic table Jan 1, 1895 Argon discovered Jan 1, 1898 Zero Group (zero valency) Jan 1, 1940 Plutonium Discovered