THE HISTORY OF THE PERIODIC TABLE Honors Chemistry Sections 5.1

Development of the Periodic Table First step – a method for accurately determining atomic mass Presented by Sanislaw Cannizzaro at the First International Congress of Chemists – 1860 First recognized method for determining atomic mass

Dimitri Mendeleev Used atomic mass and properties of elements to organize the first Periodic Table Used card and organized elements while travelling on the train Recognized that similarities in chemical properties repeated themselves at regular intervals (i.e. periods) First table published in 1869.

Mendeleev’s First Periodic Table

Exceptions to Mass Order Observed Tellurium and Iodine should be switch out of mass order based on chemical properties Also true for Argon/Potassium and Cobalt/Nickel

Mendeleev’s Predictions Predicted 3 new elements based on table design Elements had not been discovered at the time of publication of the Periodic Table

Henry Mosley 1911 – Found Periodic Table better organized by the number of protons (atomic number) This organization addressed the Te/I issue. Led to Modern Periodic Law:  The physical and chemical properties of the elements are a periodic function of their atomic number. Modern Periodic Table arranged by atomic number – Similar elements in same group/family

Noble Gases 1894 – William Strutt and Sir William Ramsay discovered Argon 1898 – Ramsey found Krypton and Xenon 1900 – Dorn finds Radon

F Block Added Lanthanides in early 1900’s Then added Actinides These elements do not have group numbers – are referred to as between Groups 3 and 4.

Periodicity