THE HISTORY OF THE PERIODIC TABLE

Honors ChemistrySections 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 designElements 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 Xenon1900 – Dorn finds Radon

F Block

Added Lanthanides in early 1900’sThen added ActinidesThese elements do not have group numbers –

are referred to as between Groups 3 and 4.

Periodicity